Delaying the international spread of pandemic influenza.
BACKGROUND
The recent emergence of hypervirulent subtypes of avian influenza has underlined the potentially devastating effects of pandemic influenza. Were such a virus to acquire the ability to spread efficiently between humans, control would almost certainly be hampered by limited vaccine supplies unless global spread could be substantially delayed. Moreover, the large increases that have occurred in international air travel might be expected to lead to more rapid global dissemination than in previous pandemics.


RESULTS
To evaluate the potential of local control measures and travel restrictions to impede global dissemination, we developed stochastic models of the international spread of influenza based on extensions of coupled epidemic transmission models. These models have been shown to be capable of accurately forecasting local and global spread of epidemic and pandemic influenza. We show that under most scenarios restrictions on air travel are likely to be of surprisingly little value in delaying epidemics, unless almost all travel ceases very soon after epidemics are detected.


CONCLUSIONS
Interventions to reduce local transmission of influenza are likely to be more effective at reducing the rate of global spread and less vulnerable to implementation delays than air travel restrictions. Nevertheless, under the most plausible scenarios, achievable delays are small compared with the time needed to accumulate substantial vaccine stocks.
Cooper
Ben S
BS
Statistics, Modelling, and Bioinformatics Department, Centre for Infections, Health Protection Agency, London, United Kingdom. ben.cooper@hpa.org.uk
Pitman
Richard J
RJ
Edmunds
W John
WJ
Gay
Nigel J
NJ
D004196:Disease Outbreaks / Q000517:prevention & control*; D014943:Global Health; D006287:Health Planning Guidelines; D006801:Humans; D053124:Influenza A Virus, H5N1 Subtype / Q000276:immunology* / Q000472:pathogenicity; D007252:Influenza Vaccines; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control* / Q000635:transmission; D007391:International Cooperation; D008962:Models, Theoretical; D013269:Stochastic Processes; D013997:Time Factors; D014195:Travel; D014611:Vaccination
D007252:Influenza Vaccines