Antiviral drugs (AVs). Australia has a large stockpile of oseltamivir. Accordingly, in this report antiviral drugs refers mainly to oseltamivir and the effectiveness parameters used in calculations relate this drug.
Attack rate. The proportion of individuals infected. Unless specified otherwise it means the attack rate achieved by the end of the epidemic.
Baseline attack rate.The eventual attack rate achieved when there are no interventionsContainment refers to the use of interventions to limit transmission, particularly during the early stages of the spread, with the aim of reducing the number of cases before a vaccine becomes available.
Delay distribution. The report expresses the effect of border control measures in terms of the delay from the time when the emergence of a pandemic strain of influenza has been declared, by WHO, until an Australian outbreak gathers momentum. This delay is random and, for brevity, its probability distribution is referred to as the delay distribution.
Deterministic model. These models ignore the chance element in transmission, so that each run of the model produces exactly the same outcome once you fix the parameter values.
Elimination refers to achieving complete fade-out of the infection from the local region.
Epidemic curve. Unless indicated otherwise, the epidemic curve refers to the graph, over calendar time, of the number of individuals who are infected but not yet removed (recovered or dead).
Eradication refers to achieving global fade-out of the infection.
Exponential growth occurs when a value increases by a multiplicative factor per unit of time. In contrast, linear growth occurs when a value increases by a constant per unit of time. For example, the series 1, 2, 4, 8, 16, 32, … is growing exponentially, whereas the series 1, 3, 5, 7, 9, 11, … is growing linearly.
Generation. Cases can be classified into generations, where the primary case(s) might make up Generation 1. All susceptible individuals who have an infectious contact with a case from Generation 1 become cases of Generation 2. Similarly for Generations 3, 4, etc. Working with generations is convenient when interest is in the reproduction number and the probability of an outbreak gathering momentum, but is less informative about the calendar-time dynamics of disease spread.
Incubation period. The time from infection until onset of symptoms.
Infectious contact. This is a contact made by an infectious individual that would lead to infection of the contacted person if the latter has no immunity and is not protected by other interventions, such as wearing a P2 mask.
Infectiousness function. The quantity that indicates how infectious an individual is as a function of the time since being infected.
Infectious period. The post infection period during which contact with the infected individual may lead to infection. The chance that infection occurs depends on the value of the infectiousness function at that time.
Latent period. The period from the time an individual is infected until the infectious period starts.
Pandemic influenza refers to a pandemic of a newly emerged strain of human influenza, as distinct from a global spread of avian influenza and world-wide spread of currently circulating human influenza strains.
Parameter. Any model constant that is unknown and needs to be estimated from data. Examples of parameters are R0, the basic reproduction number, and, the probability that an individual avoids being infected by a specific infected household member during the course of the latter’s infectious period.
Quarantine. Partial home quarantine is considered for arrivals from at-risk regions. We assume they are required to remain at home for two days, by which time they would be symptomatic if infected. Household members of such arrivals are free to mix with the wider community though, and are not quarantined until the arrival becomes symptomatic, at which point the entire household is isolated. We also consider quarantine of a household following the diagnosis of a household member. Household quarantine is continued until the household outbreak is over, but we permit partial compliance.
Reproduction number (R). When individuals are homogeneous and mix uniformly, the reproduction number is the mean number of infections generated during the infectious period of a single infective.
Basic reproduction number (R0). This is the reproduction number when there is no immunity, nor any deliberate intervention in disease transmission, i.e. when an infective meets only fully susceptible individuals.
For influenza it may be that previous exposure to currently circulating strains, or vaccinations to protect against them, provides some immunity against a newly emerged strain. In this report the basic reproduction number is taken to be the R corresponding to a community in which there has been no exposure to the emerged strain, nor any immunisation by a vaccine developed for the emerged strain.
Effective reproduction number. This is the reproduction number when interventions are in place, or a fraction of individuals are no longer susceptible.
Screening sensitivity is defined as the probability that border screening identifies an infected arriving passenger who is symptomatic.
Stochastic model. These models incorporate a chance element in transmission, so that each run of the model is likely to differ from the previous run even when the same parameter values are used