Australian Health Management Plan for Pandemic Influenza

Assumption table 1-Incubation period

Current assumption(s)

While the maximum incubation period could be seven days, a shorter incubation period of around three days would be the most common.

Planning implications

Contacts will need to be quarantined for seven days after last exposure. Modelling is to be based on the average incubation period rather than maximum.

Response implications

It is important to reassess this assumption as early as possible as it may alter recommendations about length of time contacts need to be quarantined.

Scientific rationale

Although the incubation period for seasonal influenza is short (one to three days), longer incubation periods have been recorded for human infections with influenza A/H5N1. A precautionary approach has therefore been taken until proven otherwise.

Assumption table 2-Attack rate

Current assumption(s)

2.1   The unmitigated attack rate would be in the order of 60% of which 1/3 of the cases would be asymptomatic giving an unmitigated clinical attack rate of 40%.
2.2   The mitigated clinical attack rate could be as low as 10% if all measures outlined in Part 1 of this Plan can be applied as planned and are as effective as current estimates indicate.
2.3   The attack rate in children will be higher than in adults.
2.4   The attack rates in health care settings would be very high unless effective infection control is implemented.
2.5   The attack rate in household settings is likely to be higher than other settings (except health care setting).
2.6   The attack rates may be higher in some population groups than others but it is difficult to predict which groups prior to the pandemic beginning.

Planning implications

2.1   An unmitigated pandemic would result in an unmanageable number of cases. Pandemic planning is required and mitigation strategies are warranted.
2.2   Interventions to reduce transmission are potentially very worthwhile. They would reduce case numbers, even in the event of a pandemic as severe as in 1918-19.
2.3   Interventions to reduce transmission in children may have a greater impact on reducing overall transmission rates than interventions targeting any other group. Transmission reduction strategies that target children should therefore be planned for (in conjunction with other broader population based strategies, as appropriate).
2.4   Infection control measures in health care settings should be a high priority for planning.
2.5   Management of household contacts is likely to have greater impact than interventions targeting other contacts (except health care workers). Planning should focus on strategies to identify and manage household contacts. Strategies to identify and target other contacts (e.g. workplace) should be second order priorities for planning when resources are limited.
2.6   There is a need to prepare to be able to assess the attack rates in different population groups to inform decision making. Planning should encompass strategies to target specific population groups who may have higher than average attack rates.

Response implications

2.1 - 2.2 It will be important to model the likely impact of interventions on the attack rate so as to estimate the likely health care demand in a mitigated pandemic. It will be important to assess the impact of interventions on the attack rate continually in order to assess overall effectiveness.
2.3   Early in the pandemic, it will be important to establish the differences in the rate of accumulation of cases in adults compared with children to assess the likely effectiveness such as school closures. Later in the pandemic robust estimates of age specific attack rates may be useful in supporting decision making with regards to use of initial doses of customised vaccine.
2.4   It will be important to collect data to assess the effectiveness of infection control measures in health care settings and to be able to adjust recommendations if needed.
2.5 - 2.6 It will be important to collect data on attack rates in different population groups to allow tailoring of public health interventions especially during the SUSTAIN phase.

Scientific rationale

2.1   Expert opinion based on past pandemics.
2.2   Clinical attack rates in the 1918 pandemic were thought to be lower than that reported during the 1957 and 1968 pandemics.
2.3 - 2.4 Extrapolation from data of seasonal influenza and from the 1957 and 1968 pandemics.
2.5 - 2.6 These are based on modelling and expert opinion.

Assumption table 3-Modes of transmission

Current assumption(s)

3.1   Droplet and contact spread will be the major modes of transmission in the community.
3.2   Specific procedures within the health care setting may lead to the generation of clinically significant aerosols.
3.3   Vertical transmission is a possibility that would need to be assessed early in a pandemic.
3.4   Oro-faecal transmission seems unlikely but would need to be excluded early in the pandemic.
3.5   The risk of transmission of pandemic influenza via blood is considered unlikely but conceivable.

Planning implications

3.1   Infection control in the community should focus on droplet and contact precautions.
3.2   Health service planning should include the possibility of aerosol transmission.
3.3   Infection control planning for obstetrics and neonatal units is required. Preparations should be made to collect data to assess the issue of vertical transmission early in the pandemic.
3.4   Preparations should be made to collect data to assess the possibility of
oro-faecal transmission early in the pandemic. Infection control should include the possibility that faeces may be infectious, but should focus on preparing to implement infection measures to address the other, more likely, routes of transmission.
3.5   A precautionary working assumption that viraemia is possible during the first week of illness should be adopted. Standard precautions to protect against blood borne viruses should be maintained at all times. Pandemic influenza affected individuals should not donate blood for up to 4 weeks post the onset of illness or while symptomatic.

Response implications

3.1 - 3.2 It will be important to confirm this assumption early in the pandemic so as to re-affirm or amend infection control guidance.
3.3   As data may not be available until later in the pandemic, responses should assume that vertical transmission could occur until data indicates otherwise.
3.4   It will be critical to exclude this as a significant mode of transmission early in the pandemic. If oro-faecal transmission appears to play a role in transmission, infection control and transmission reduction interventions may need to be modified significantly.
3.5   Planning and response should be based on the assumption that blood borne transmission could occur until data indicates otherwise. Data may not be available until later in the pandemic. If blood supplies become critical, it may be important for rapid study in this area.

Scientific rationale

3.1   Droplet and contact transmission have been demonstrated as the major routes of transmission for seasonal influenza. The patterns of transmission in previous pandemics also indicate that these were dominant routes of transmission.
3.2   Certain procedures performed in health care settings such as but not limited to bronchoscopy, intubation, and nebulizer treatment can create aerosols.
3.3   Although vertical transmission has not been documented for seasonal influenza and there is very limited data available to assess whether vertical transmission occurred during previous pandemics, there is some indication from a very small case series that vertical transmission may occur with influenza A/H5N1.
3.4   Avian influenza is predominately an oro-faecal disease in birds/animals. Over 50% of patients with influenza A/H5N1 experience diarrhoea, and gastrointestinal disturbance have been reported as a presenting symptom. Influenza A/H5N1 can be isolated from faeces and small intestine viral infiltrates have been noted in a very small number of post-mortem examinations. It is unclear whether these findings are due to primary or secondary infection. Expert opinion is that this issue should be studied early in the pandemic.
3.5   Although viraemia is not associated with seasonal influenza, there is some evidence to indicate that viraemia does occur in some patients with influenza A/H5N1. A precautionary approach is therefore recommended.

Assumption table 4-Period of communicability

Current assumption(s)

4.1   Cases of all age groups could be infectious from one day (24 hours) before the onset of symptoms. Persons who become ill may shed virus (and transmit infection) for up to one day before onset of symptoms.
Peak shedding occurs in the first two days of illness.
4.2   Children will shed greater amount of virus, and may shed for longer. Adults >65 years may also be infectious for a longer period.
4.3   Cases would be most infectious in the first few days after the onset of symptoms. It is likely that, for the vast majority of cases of all ages, infectiousness would decline rapidly after 5 days of illness, particularly if accompanied by a decline in symptomatic illness.
4.4   Antivirals are likely to reduce respiratory viral shedding. It is unclear (i) to what extent this occurs (ii) whether viral shedding in faeces (if it occurs) would be reduced by antiviral treatment and (iii) whether vertical transmission (if it occurs) would be reduced by the use of antivirals.

Planning implications

4.1   Quarantining of contacts even if asymptomatic will be required as it is assumed that the onset of the period of communicability will pre-date the onset of symptoms by up to 24 hours.
4.2 - 4.4 The standard period for isolation is seven days or until the resolution of fever (if that period is longer).

Response implications

4.1   It is unlikely that early definitive evidence would be available that would allow experts to conclusively state that the period of communicability does not begin before the onset of symptoms. It is possible although unlikely that the period of communicability prior to the onset of symptoms might be longer than assumed. If there were data to support this, contact definitions may need to be amended.
4.1 - 4.4 It is likely that the standard period of isolation would be amended during the pandemic as information becomes available about the characteristics of the virus and the disease it causes as well as the impact on shedding of antiviral treatment. It will be important to reassess the period of communicability early on in the pandemic.

Scientific rationale

4.1   There are a small number of studies that appear to indicate that persons with seasonal influenza could be infectious a number of hours before the onset of discernable symptoms. A precautionary approach has therefore been taken.
4.2 - 4.4 Isolation periods are based on data from seasonal influenza viral shedding in different, untreated (i.e. no antivirals) population groups and from a small number of case studies of influenza A/H5N1 patients. There are some data to suggest that antiviral treatment reduces shedding of virus from the respiratory tract. Experts believe that this effect is likely to occur with pandemic virus.

Assumption table 5-Respiratory protection zone

The respiratory protection zone is the area around an infected patient where airborne viral particles or large droplets could lead to direct respiratory or conjunctival infection.
This box provides an overview of the advice about the respiratory protection zone, the detailed practical advice will be provided in the Clinical and Infection Control Annex (see Appendx B).
Size of zone of transmission around an infectious patient when no aerosol generating procedures are undertaken.
The zone of transmission will be the same in all health care settings. One metre is the minimum distance.
Size of zone of transmission around an infectious patient when aerosol generating procedures are undertaken.
The transmission zone when aerosol generating procedures are undertaken is the room occupied by the patient at the time, except where full-length curtains or barriers enclose a space then the zone is the enclosure. The room is defined as a patient care space consisting of any non-temporary walls/barriers/curtains.
The assumptions below focuses only on the respiratory protection zone. For surface contamination see Assumption 6.

Current assumption(s)

5.1   Scenario: The infectious case is wearing a surgical mask thus no aerosol generating procedures are possible.
        The surgical mask worn by the patient is likely to act as an effective barrier against droplet transmission.
5.2   Aerosol generating procedures (which, due to the techniques involved, can not be performed with the case wearing a mask) will result in:
        a) generation of fine, airborne viral particles
        b) propulsion of those particles through the air within the room that the case has occupied.
5.3   Scenario: Infectious case is not wearing a mask but no aerosol generating procedures are undertaken.
        As the main route of transmission in these circumstances will be through large droplets that quickly fall to the ground, it is unlikely that there will be significant amounts of airborne viral particles beyond a one-metre radius of the case. However within the one-metre radius there are likely to be airborne viral particles that, if inhaled or in direct contact with conjunctiva of an unprotected, non-immune individual, could result in infection.

Planning and response implications

When practical, every attempt should be made within the clinical setting to cohort mask wearing and non-mask wearing patients. If not possible, required protection should be in line with that for treating the highest risk patient in the room.
5.1   Mask and eye protection: Protection with a surgical mask and eyewear* is required for people within one metre of an infectious case who is wearing a mask (unless the patient wearing a mask cannot keep it in place, e.g. because of extreme coughing). No respiratory or eye protection is required if greater than one metre away from the case**.
        Antiviral protection: A non-immune health care worker continuously caring for a patient within one metre is likely to be on pre-exposure prophylaxis. If not, post-exposure prophylaxis should be offered.
5.2   Mask and eye protection: Protection with a P2 mask (or Powered Air Purifying Respirator (PAPR), if available) and eyewear* is required for all people in the room with the infectious case whilst aerosol generating procedures are taking place. Note: PAPRs are specialised devices that will be in short supply.
        Antiviral protection: If a non-immune health care worker is likely to be exposed to aerosol-generating procedures, pre-exposure antivirals should be taken preferably two hours before the exposure or as soon after exposure as possible.
        If a non-immune health care worker is likely to be continually exposed to aerosol-generating procedures performed on infectious cases, continuous prophylaxis with antivirals should be offered.
        If in the unforeseen circumstance of no pre-exposure prophylaxis, post-exposure prophylaxis should be provided within 48 hours.
5.3   Mask and eye protection: Protection with a P2 mask and eyewear* is required for people who are within one metre of an infectious case who is not wearing a mask (or if a patient wearing a mask cannot keep it in place, e.g. because of extreme coughing). No respiratory or eye protection is required if a distance of one metre or greater is kept from the case**.
        Antiviral protection: A non-immune health care worker continuously caring for a patient within one metre is likely to be on pre-exposure prophylaxis. If not, post-exposure prophylaxis should be offered.
Notes:
             *in addition to gloves and disposable gown
             **Hand washing to prevent contact transmission is required by all persons in areas where surface contamination may have occurred. For staff involved in surface cleaning of potentially contaminated areas particularly if this cleaning involves sweeping or scrubbing, respiratory protection with a surgical mask and eye protection as well as gloves and gown are required.

Scientific rationale

See assumption 3 for details about the modes of transmission.
The assumptions are based on:
•     studies of aerosol generating procedures for both seasonal influenza and SARS
•     field studies on the effectiveness of surgical masks worn by infectious patients used to estimate the likely impact of this intervention in reducing risk to others.

Assumption table 6-Survival of the virus

Current assumption(s)

6.1   Survival on surfaces-the virus could survive if unwashed/undisturbed and be potentially infectious for the following lengths of time:
        a) on hard non-porous surfaces such as stainless steel and plastic for up to 48 hours
        b) on cloth, paper and tissues for up to 12 hours
        c) on surfaces contaminated with blood or faeces for longer than normal surface survival due to the presence of increased concentration of organic matter, up to 5 days under ideal conditions.
6.2   Disinfection-the use of normal household detergents with standard cleaning procedures would inactivate or remove virus on any of the above surfaces.
6.3   Survival on hands-pandemic influenza virus will be able to survive on unwashed hands for up to 30 minutes.
6.4   Hand washing-washing with soap and water for 15-20 seconds or appropriate use of alcohol-based hand rubs would remove the virus.
6.5   Cadaver-viable virus may be found within a cadaver for several days, possibly weeks after death, particularly if the body has been refrigerated.

Planning and response implications

6.1-6.5 Areas where an infectious case has spent time, particularly if the infectious case is not wearing a surgical mask, are likely to be contaminated. They will pose a risk to others through contact contamination and transference of viral particles. Hand washing and surface cleaning will be extremely important in reducing the risk of this occurring. Use of soap and water/alcohol rubs and standard cleaning materials will be effective in disinfecting contaminated areas. No special cleaning procedures or materials would be required during a pandemic.
        Special precautions will be required for people handling cadavers. These will be outlined in the Funeral Annex and Pathology Annex.

Scientific rationale

6.1- 6.5 Research into seasonal influenza, avian influenza (influenza A/H5N1) and SARS have been used to estimate survival times on different surfaces and in cadavers. A precautionary approach has been taken and maximum possible survival times are quoted above. It should be noted that true infectiousness to humans of viruses at the extremes of these survival times is likely to be extremely low.
        Research into the effectiveness of different cleaning materials for seasonal and avian influenza and for SARS and other similar enveloped viruses was used to estimate likely effectiveness of these materials against the pandemic influenza virus.

Assumption table 7-Serial interval

Current assumption(s)

The current assumption is that the serial interval will be two to four days.
Serial interval in this context is defined as the average length of time between the primary case developing symptoms and the secondary case developing symptoms.

Planning implications

As the serial interval is assumed short, contact tracing must take place as quickly as possible for it to be effective.

Response implications

Serial interval estimate, along with attack rate, will be required to be able to model the likely impact.

Scientific rationale

Serial interval has been extrapolated from seasonal influenza and past pandemic data.

Assumption table 8-Presenting symptoms

Current assumption(s)

The current assumption is that the predominant presenting symptoms during a pandemic will be respiratory symptoms and fever usually accompanied by systemic symptoms such as myalgia and fatigue.
Fever may not be present in the elderly and atypical presentations may be more common at the extremes of age.

Planning implications

Screening programmes, surveillance and clinical case definitions should be based around fever and/or respiratory symptoms.

Response implications

It will be a high priority to understand the spectrum of presenting symptoms to allow modifications to case (surveillance and clinical) definitions as early as possible to ensure the appropriate levels of sensitivity and specificity. It will be important early in a pandemic to establish the frequency of atypical presentations as amendments, particularly to the clinical case definitions, may be required.

Scientific rationale

Extensive studies of seasonal influenza and previous pandemics indicate that influenza is predominately a respiratory disease. However, atypical presentations of seasonal influenza can occur particularly in those at the extremes of age and in patients with unusual influenza viruses such as influenza A/H5N1. It is therefore possible that pandemic influenza could present with high frequency of atypical symptoms.

Assumption table 9-Health impact of pandemic influenza

Current assumption(s)

9.1   The current assumption is that in an unmitigated pandemic (i.e. no antivirals, no antibiotics) the clinical case fatality rate would be 2.4%.
9.2   It is estimated that with the appropriate medical care (early antiviral and antibiotic therapy as needed and supportive care for those with more severe illness) the death rate could be halved that is, the clinical case fatality rate would be 1.2% with treatment.
9.3   A W shaped mortality distribution, similar to that seen in the 1918 pandemic, has been assumed for planning purposes with three mortality rate peaks-under 5 year olds, over 65 year olds and 20 to 35 year olds.
9.4   A similar range of complications would be encountered as currently experienced with seasonal influenza namely, predominately respiratory complications for all age groups, rise in cardiovascular events in adults and the elderly, and a small proportion of children presenting with neurological complications. The frequency of all complications would be greater in a pandemic than with seasonal influenza.
9.5   Maternal mortality and early foetal loss are likely to be significant.
9.6   The immunosuppressed and those with underlying serious medical conditions would experience higher complications than those without underlying health problems.
9.7   Psychosocial and mental health needs are likely to be high and demand for these services may extend into and even beyond the recovery period.

Planning implications

9.1 - 9.2  Planning should ensure that the use of antiviral, antibiotics and appropriate supportive health care during a pandemic could be optimised.
9.3   Paediatric and elderly care health services will be in demand and planning should ensure that these services could be readily optimised. The possibility of a high health impact in the young working age group needs to be incorporated into business continuity and social service planning arrangements.
9.4   Respiratory and cardiovascular services will likely be in high demand and planning should ensure that these services could be optimised.
9.5   Obstetric and neonatal services should be included in health service planning.
9.6 - 9.7  Certain specialist health care services may be required to ensure that the specific needs of these groups can be best met. Social support and community resilience will also be important and should be included in whole of government planning.

Response implications

9.1 - 9.6   Data on health service usage needs to be closely monitored throughout the pandemic and services optimised as required.
9.7   Transition of services during the CONTROL period will need to take into account the psychosocial and mental health needs of the population, which may extend well into recovery.

Scientific rationale

9.1   and 9.3 are based on data from the 1918 pandemic.
9.2   Data from the 1918 pandemic appears to indicate that at least 50% of the deaths were late deaths that is, they occurred ten days or more after the onset of illness. The majority of these deaths are likely to have been the result of secondary bacterial pneumonia for which, at the time, there would not have been any antibiotic treatment. Expert opinion is that early and appropriate use of antivirals (+ pneumococcal vaccine in high-risk groups) is likely to prevent 50% of such complications occurring in the first place. For the secondary bacterial pneumonias that do occur, antibiotics and supportive care would further reduce the death rate by at least another 50%.
9.4   This is based on data regarding hospitalisation during seasonal influenza outbreaks in Australia.
9.5 - 9.6  This is based on data from seasonal influenza, recent H5N1 infection in humans, and small amount of data from analysis of previous pandemics.
9.7   This is based on data from natural disasters and mass casualty events.

Assumption table 10-Treatment with Neuraminidase Inhibitor (NI) antivirals

Note that Assumptions 10 and 11 are based on the presumption that:
A NI antiviral either oseltamivir or zanamivir will be used for treatment or prophylaxis. A full assessment of the possible effectiveness of the adamantines (amantadine and rimantidine) has not been undertaken due to the current high rates of resistance that the influenza virus demonstrate against this class of antiviral drugs.
Sensitivity of the pandemic virus to NI antivirals is high.
Effectiveness will be monitored during a pandemic.

Current assumption(s)

10.1 Timing-NI antiviral treatment during the pandemic would likely be most effective if started within 48 hours of onset of illness. Limited therapeutic benefit is likely to be seen when treatment is started later than five days post onset of systemic symptoms (myalgia +/ fever).
10.2 Dosage-the current recommended doses and contra-indications should be used for planning purposes. There is currently no evidence to support the use of combination therapy.
10.3 Effect on mortality-for planning purposes it is assumed that:
(a) Early NI antiviral treatment may have some impact on reducing early mortality (i.e. death within ten days of onset of illness) by reducing overall viral load.
(b) Early NI antiviral treatment is likely to have significant impact in the prevention of complications due to secondary bacterial infections (up to 50% reduction) and that by reducing secondary bacterial complications, this is likely to lead to a significant reduction in late mortality (death after ten days of onset of illness).
10.4 Effect on morbidity-the early use of NI antiviral medication (i.e. started within 48 hours of onset of symptoms) is anticipated to result in reduction:
(a) in pneumonia in at risk adult population by 40%
(b) in pneumonia in previously healthy adults by 50%
(c) in pneumonia in children by 40%
(d) in otitis media in children by 30%.
10.5 The potential impact of NI antiviral therapy on maternal mortality and neonatal outcomes is impossible to predict at this stage. Early clinical trials will be needed to inform guidance in this area.
10.6 The precise clinical indications and population groups that would benefit most from NI antiviral therapy are difficult to predict prior to the onset of a pandemic.

Planning and response implications

10.1 - 10.6  Planning should therefore focus on developing the capacity to identify cases as early as possible in the course of their illness and on optimising services so that NI antiviral therapy, if clinically indicated, can be administered within 48 hours. The clinical benefit of treatment provided to cases that present after 48 hours onset will need to be evaluated at
the time.
        Dose levels and length of treatment for adults and children should be kept under review.
        Preparedness and response also needs to ensure that, if required, there is the capacity to target NI antiviral therapy at the appropriate high risk/high need population groups. Rapid analysis of outcomes of the use of NI antivirals in the early stage of the pandemic will be needed to inform development of guidance in this area.
        Combination therapy needs to be considered in the future particularly if drug resistance becomes an issue.

Scientific rationale

10.1 This is based on data from seasonal influenza and outcomes of a small, non-randomised case study of a limited number of patients with influenza A/H5N1. In contrast to uncomplicated seasonal influenza, oseltamivir treatment is warranted for patients presenting later with H5N1 virus because viral replication is more prolonged than with seasonal influenza.
10.2 Refer to MIMS 2008.
10.3 There are currently only limited data from small trials with seasonal influenza available upon which to estimate possible impact of NI antivirals on mortality. However, given the strength of the data supporting the finding that early NI treatment in seasonal influenza results in significant reduction in complications (see 10.4 below) and the knowledge that over 50% of deaths in 1918 were likely due to these complications, expert opinion is that early antiviral treatment could have an appreciable impact on mortality during a pandemic.
10.4 There is a relatively large body of evidence indicating that early NI antiviral therapy reduces complications. The data for use in seasonal influenza indicates complication reduction rates greater than the estimates above. However, a precautionary approach was taken in extrapolating from seasonal influenza to pandemic influenza and hence lower estimates of likely effectiveness have been assumed for pandemic influenza compared with documented results for treatment in seasonal influenza.
10.5 - 10.6  This represents the consensus view of an expert committee

Assumption table 11-Antiviral prophylaxis with Neuraminidase Inhibitor (NI) antivirals

Current assumption(s)

11.1 Dosage-the current recommended doses for prophylaxis is assumed to be effective against the pandemic strain.
11.2 Pre-exposure prophylaxis
        Pre-exposure prophylaxis should preferably begin two hours before exposure.
        The maximum recommended length for continuous prophylaxis should be six weeks for oseltamivir and four weeks for zanamivir until further data becomes available.
        People on continuous pre-exposure prophylaxis need a periodic break from taking the drug.
11.3 Post-exposure prophylaxis
        Post-exposure prophylactic antivirals started within 48 hours of exposure would result in a 50% reduction in laboratory confirmed secondary cases.
        Post-exposure prophylaxis will be most effective if taken as early as possible and within 48 hours of exposure. It is unlikely to have any significant impact if started more than 48 hours post-exposure.
        Ten days of post-exposure prophylaxis is required after last known exposure.

Planning implications

11.1 Dosage-For planning purposes, the dosage recommended in the Interim National Pandemic Influenza Clinical Guidelines (June 2006) should be followed.
11.2 Planning should focus on ensuring that pre-exposure antivirals are available to be taken before exposure is likely.
        As seven days of prophylaxis is needed after last exposure, followed by a seven day break from taking the drug, a health care worker on continuous prophylaxis would require:
        - two weeks away from the high risk setting for every five weeks worked in that setting for oseltamivir.

        - two weeks away from the high risk setting for every three weeks worked in that setting for zanamivir.

        This needs to be taken into consideration when planning staff rosters in high-risk health care services where continuous prophylaxis might be used.
11.3 Planning should focus on developing the capacity to identify contacts as early as possible and on optimising services so that antiviral post-exposure prophylaxis can be administered quickly.
        Any contact that is identified too late for post-exposure prophylaxis should be quarantined and monitored for symptoms for seven days post-exposure. These contacts should be offered early antiviral therapy if they develop symptoms. Planning needs to develop capacity to both monitor these contacts and provide early therapy if required.

Response implications

11.1 - 11.3 The effectiveness of prophylaxis, post-exposure and continuous pre-exposure, needs to be monitored and evaluated so that policies can be tailored during a pandemic to best meet the needs and ensure effective use of resources.
The duration of post-exposure prophylaxis will be reviewed if evidence is available that this period could be reduced.

Scientific rationale

11.1 The current dose recommendations are based on data from a relatively small number of clinical trials that have been conducted to examine the safety and effectiveness of NI antiviral prophylaxis.
11.2 There are currently no data available on continuous use of oseltamivir beyond six weeks or zanamivir beyond four weeks. The recommendation that a break is required between continuous courses is a precautionary recommendation only.
11.3 Data from a small number of clinical trials indicates that early post-exposure NI antiviral prophylaxis for seasonal influenza reduces secondary cases by up to 70%. A precautionary approach was taken in extrapolating from experiences with seasonal influenza and translocating these experiences into assumptions about a novel, unknown pandemic virus that could have greater transmissibility than seasonal influenza. Hence, lower estimates of estimated impact on secondary case prevention have been assumed for pandemic influenza.

Assumption table 12-Immunity following natural infection

Current assumption(s)

12.1 For planning purposes, it should be assumed that all individuals, regardless of age, would be vulnerable to pandemic influenza that is, no natural prior immunity will be present in any age groups.
12.2 It is assumed that individuals who have recovered from natural infection will have a reasonably high degree of protection from a second infection within the same wave should a second distinct wave occur. However, as subsequent waves may be due to a drifted virus, it cannot be assumed that an individual who experienced pandemic influenza in an initial wave would be fully protected in any subsequent waves.

Planning implications

12.1 Planning should be based on the assumptions that no natural prior immunity will exist and hence protection may be required by all members of the population.
12.2 Planning for the first wave response can assume that natural infection will confer a high degree of protection during that wave. However planning for second and subsequent waves (based on the assumption that the virus will drift), should be based on the assumption that immunity developed in the community as a result of infection during previous waves may not be fully protective against subsequent waves.

Response implications

12.1 As the first wave progresses, immunity post infection should be assessed. If immunity is high, then, in certain circumstances, protective measures for recoverees could be reduced.
12.2 If subsequent waves progress, data should be collected to see if previous infection is conferring protection against the second/subsequent wave pandemic virus. If immunity is high, then, in certain circumstances, protective measures for recoverees could be reduced. The level of protection in second waves following natural infection will be assessed at the time as a priority.

Scientific rationale

12.1 - 12.2 Based on data from previous pandemics and particularly from analysis of the 1918 pandemic in Australia where infection during the first wave appeared (for some individuals at least) not to confer protection against second infection during the second wave.

Assumption table 13-Immunity following vaccination

Current assumption(s)

13.1 It is assumed that if the viral strain in the candidate pandemic vaccine were closely related to the pandemic strain (i.e. if both the candidate vaccine strain and the pandemic strain were both influenza A/H5N1 viruses), then some degree of protection would be afforded following two doses of candidate vaccine. The level of protection would not be known until testing could be conducted and it should be assumed that at least one dose of customised pandemic vaccine is likely to be needed to ensure adequate protection against the pandemic virus.
13.2 If a person has received the customised pandemic vaccine and have received two doses 21 days apart, it is assumed they are fully vaccinated seven days after the second dose.
        For those individuals who receive a priming course of candidate vaccine that contains a similar viral strain to the pandemic virus, protective levels of antibodies are likely to occur very quickly, within seven days, after one dose of customised vaccine.

Planning and response implications

13.1 Anyone who has received two doses of candidate vaccine will require at least one dose of customised pandemic vaccine.
13.2 Without priming, it will take at least 28 days for protection to be developed using customised pandemic vaccine.
        The use of continuous pre-exposure antiviral prophylaxis will be reviewed once the efficacy of the candidate and customised vaccine is determined.
        If the customised vaccine is effective, continuous pre-exposure antiviral prophylaxis will be ceased 14 days after a health care worker has received a second dose of customised vaccine. While it is assumed that antibodies will occur 28 days after the initial dose of customised vaccine (or seven days after receiving the second dose of customised vaccine, thus fully vaccinated), a further week on antiviral prophylaxis should be provided in the absence of further evidence.
        It is envisaged that most frontline health care workers on continuous pre-exposure prophylaxis will have received two doses of the candidate vaccine. These individuals will only need one dose of customised vaccine. They will be considered fully vaccinated seven days after the customised vaccine dose but should continue antiviral prophylaxis for a further seven days as a precautionary measure.

        Data should be collected to see if vaccination is conferring protection against the second/subsequent wave pandemic virus. The level of protection in second waves following vaccination/natural infection will be assessed at the time as a priority.

Scientific rationale

The above is based on data from a range of clinical trials that have been conducted on candidate pandemic vaccines as well as data about immune responses to seasonal influenza in relatively naive populations (i.e. young children).

Assumption table 14-Absenteeism

Current assumption(s)

14.1 30 to 50% of the working age population could be away from work during the peak of the pandemic. This includes absenteeism due to illness or quarantine, the need to stay at home to care for someone who is ill, the need to stay at home to look after children in the event of school closures, fears about being infected at work as well as some people fulfilling other roles in the community. In certain sectors, absenteeism may be higher due to the high percentage of female employees (e.g. health care, especially in nursing, pharmacy).
14.2 Working age adults who develop pandemic influenza would be quarantined and unable to come to work, because they could be infectious to others, for seven days after the onset of symptoms.
14.3 Working age adults who develop pandemic influenza would, on average, require 14 days recovery that is, it would take 14 days from the onset of symptoms to be fit enough to return to normal activities.

Planning and response implications

14.1 - 14.3 Business continuity needs to assume and plan for high and possibly fluctuating levels of absenteeism throughout the pandemic.
        Communication strategies need to ensure that the public are kept well informed and that fears and concerns are addressed.

Scientific rationale

14.1 - 14.3 The evidence base for this is extremely limited, and thus represents the consensus view of an expert committee.

Assumption table 15-Duration of pandemic disruption

Current assumption(s)

The pandemic in Australia will last 7-10 months.
Recovery is likely to take a further six months to a year depending on how severe the pandemic has been.

Planning and response implications

Business and the community need to plan to be able to continue to function despite the disruptions for up to one year. Business continuity needs to take into account the likely fluctuating levels of disruptions and possible differences in timing of interventions across the country.

Scientific rationale

The evidence base for this is extremely limited, and thus represents the consensus view of an expert committee.