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During the early stages of a new influenza pandemic, travel restriction is an immediate and non-pharmaceutical means of retarding incidence growth. It extends the timeframe of effective mitigation, especially when the characteristics of the emerging virus are unknown. Chong and Chung (2012) describe a study in which they used the 2009 influenza A pandemic as a case study to evaluate the impact of regulating air, sea, and land transport. Other government strategies, namely, antivirals and hospitalizations, were also evaluated.
Hong Kong arrivals from 44 countries via air, sea, and land transports were imported into a discrete stochastic Susceptible, Exposed, Infectious and Recovered (SEIR) host-flow model. The model allowed a number of latent and infectious cases to pass the border, which constitutes a source of local disease transmission. The researchers also modeled antiviral and hospitalization prevention strategies to compare the effectiveness of these control measures. Baseline reproduction rate was estimated from routine surveillance data.
Regarding air travel, the main route connected to the influenza source area should be targeted for travel restrictions; imposing a 99 percent air travel restriction delayed the epidemic peak by up to two weeks. Once the pandemic was established in China, the strong land connection between Hong Kong and China rendered Hong Kong vulnerable. Antivirals and hospitalization were found to be more effective on attack rate reductions than travel restrictions. Combined strategies (with 99 percentÂ restriction on all transport modes) deferred the peak for long enough to establish a vaccination program.
The researchers say their study suggests that air travel restrictions should be priorities for consideration when a new influenza pandemic begins overseas. When the pandemic is initiated in China or other places where there is land travel to Hong Kong, land travel restrictions should also be a priority. If restrictions are able to cover 99 percent ofÂ travelers with the use of antiviral and hospitalization, the resulting pandemic delays are possible to allow vaccine production; if the restrictions cannot cover 90 percentÂ or more of travelers, then the peak time will happen sooner. In this case, control
measures such as antiviral should be enacted earlier to alleviate the epidemic growth. To date, travel restrictions have yet to gain widespread social acceptance, but the benefits may significantly outweigh the costs, especially
when a new and highly intrusive virus emerges. Their research is published in BMC Infectious Diseases.
Reference: Chong KC and Chung Zee BC. Modeling the impact of air, sea, and land travel restrictions supplemented by other interventions on the emergence of a new influenza pandemic virus. BMC Infectious Diseases 2012, 12:309 doi:10.1186/1471-2334-12-309