Travel Restrictions Slow, but Do Not Stop, Pandemic
Sealing international borders, a tactic debated as a way to slow the spread of other contagious diseases, delayed the spread and peak of influenza pandemics from a few days to 4 months but, ultimately, on its own, it could not prevent dissemination of influenza, according to a systematic review.
Dr. Ana L.P. Mateus, from the Field Epidemiology Training Programme, Public Health England (East Midlands Office), Nottingham, United Kingdom, and colleagues report the findings of their metaanalysis online September 29 in theBulletin of the World Health Organization.
According to the authors, the World Health Organization (WHO) in 2007 included travel restrictions in an interim protocol aimed at rapidly stemming the initial emergence of pandemic influenza. Once a pandemic is established, however, WHO takes a dim view of such travel restrictions because of their effect on global travel and trade. Nonetheless, the strategy gained favor in 2009 as countries attempted to avert the arrival of A(H1N1) influenza virus.
In their review of 23 studies, the authors found initially positive outcomes with "extensive travel restrictions" that limited more than 90% of movement, but those beneficial effects were erased when the transmissibility of the viral strain increased. Internal travel bans could delay pandemic spread by roughly 1 week, but international travel restrictions reduced pandemic attack rates by less than 0.02%. Banning air travel by children may be effective but, the authors argue, is "socially impractical."
At the local level, travel restrictions "appeared to have limited effectiveness in the containment of influenza," the authors write. In Mongolia, for instance, a simulation restricting road and rail travel by 95% resulted in a 0.1% reduction in the pandemic attack rate. Likewise, in the United States, travel restrictions that were 99% effective in barring entry of infected travelers resulted in a delay of pandemic spread by just 2 to 3 weeks.
In densely populated England, Scotland, and Wales, a combination of internal and international travel could help to stagger the effect of the pandemic across the United Kingdom, the authors write, but at the international level, travel restrictions had "limited effectiveness," with a 40% restriction of air travel delaying by less than 3 days the march of A(H1N1) from Mexico to other countries.
A pandemic that began in Sydney, Australia, or Hong Kong would take 2 to 3 weeks longer to arrive in the United States if 95% of air travel were restricted. Selectively canceling one quarter of flights connecting between 500 of the globe's major cities, however, would pack more bang for the preventive buck, with an additional 19% reduction in infected travelers.
Travel restrictions that exceeded 90% could delay the spread of pandemics by up to 4 months for low to moderately transmissible strains, but with highly transmissible strains, such travel bans "appeared ineffective."
"The results of our systematic review indicate that overall travel restrictions have only limited effectiveness in the prevention of influenza spread, particularly in those high transmissibility scenarios," the authors write. "Only extensive travel restrictions — i.e. over 90% — had any meaningful effect on reducing the magnitude of epidemics. In isolation, travel restrictions might delay the spread and peak of pandemics by a few weeks or months but we found no evidence that they would contain influenza within a defined geographical area."
The authors reviewed evidence from modeling studies published before May 2014 and excluded studies that only examined disease spread among animals. The researchers included 23 studies, 19 of which were mathematical modeling studies.
"It seems likely that, for delaying the spread and reducing the magnitude of an epidemic in a given geographical area, a combination of interventions would be more effective than isolated interventions," the author conclude. "Travel restrictions per se would not be sufficient to achieve containment in a given geographical area, and their contribution to any policy of rapid containment is likely to be limited."
The University of Nottingham Health Protection and Influenza Research Group, which employs three of the study authors, disclosed receiving research funds from GlaxoSmithKline and unrestricted educational grants for influenza research from F Hoffmann-La Roche and Astra Zeneca. Among those three authors, one author further disclosed receiving funding before October 2010 to attend influenza-related meetings, give lectures, and received research funding from several manufacturers of antiviral drugs and influenza vaccines. This same author disclosed being an employee of SmithKline Beecham, Roche Products, and Aventis-Pasteur MSD before 2005. The remaining authors have disclosed no relevant financial relationships.
Bull World Health Organ. Published online September 29, 2014. Full text