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‘What is clear is that it is when, not if.’ Frederick Hayden, University of Virginia School of Medicine, 2011.
There are more factors that are not known about a future influenza pandemic than that are known (see Table 2). The uncertainty factor makes preparedness particularly challenging.
While the 2009 pandemic was considered mild, future emerging pandemic virus strains may be highly pathogenic.18 The impact of a future pandemic will depend on its transmissibility and severity.20
Table 2. What can and cannot be assumed about future influenza pandemics
What can probably be assumed or predicted
What cannot be assumed
- Mode of transmission (droplet or contact)
- Incubation time (likely to be short)
- When a person becomes infectious
- Clinical presentation (influenza symptoms)
- The general effectiveness of standard precautions (hand hygiene, cough etiquette)
- Age groups with most transmission
- Who will be the most susceptible
- Precise periods of viral shedding in different age groups
- The severity of the pandemic and fatality rates
- How well immunity occurs
- Precise clinical case definition and complicating conditions
- Whether the new virus will dominate over seasonal type A influenza
- Susceptibility or resistance to antivirals
- Effectiveness of drug and non-drug interventions
- Safety of drug interventions
Adapted and reproduced with permission from European Centre for Disease Prevention and Control (ECDC).