Vaccination, antivirals, social distancing may blunt H1N1's impact, study suggests

The relatively low number of new cases created by a single case of H1N1 influenza indicates that mitigation strategies such as vaccination, social distancing and the use of antiviral drugs may help lessen the final impact of the virus, suggests an epidemiological modeling study reported Dec. 3 in the Canadian Medical Association Journal.

The study looked at data from laboratory-confirmed cases of H1N1 between April 13 and June 20, 2009, in Ontario, Canada, and performed 1,000 simulations to estimate epidemiological parameters for the virus. These findings, reported by, may be useful to policymakers in managing the pandemic.

"Because the 2009 influenza pandemic continues to evolve, these values are critical for planning and can be used to reduce some of the uncertainty around the health burden likely to be associated with this disease in the coming months," writes Dr. David Fisman of the Dalla Lana School of Public Health, University of Toronto, and his co-authors.

The study found that the median incubation period for H1N1 influenza was four days and the duration of symptoms seven days. Patients ages 18 years and younger recovered more quickly than older patients and the risk of hospital admission among laboratory-confirmed cases (who likely represented 1 percent to 10 percent of total cases) was 4.5 percent.

People younger than 1 year of age and older than 65 were at higher risk of hospital admission. Adults older than 50 made up 7 percent of cases but accounted for seven of 10 initial deaths.

According to the study's estimates, the characteristics of the H1N1 virus are similar to those of seasonal influenza. "However, when combined with high attack rates in younger groups, there may be greater absolute numbers of hospital admissions and deaths than are observed in a typical influenza season," write the authors, although this may be attributed to enhanced surveillance during a pandemic.