One In Five People Infected During 2009 H1N1 Flu Pandemic
January 25, 2013

One In Five People Infected During 2009 H1N1 Flu Pandemic

Lee Rannals for — Your Universe Online

A new study shows that at least one in five people in countries including India, Australia and the U.K. were infected with influenza during the first year of the 2009 H1N1 pandemic.

Forty-seven percent of those infected were aged between five and 19, researchers said. Older people were less likely to have become infected, with eleven percent of people over the age of 65 becoming infected.

They wrote in the journal Influenza and Other Respiratory Viruses that 20 to 27 percent of people studied were infected by the pandemic during the first year of circulation. They believe the incidence of influenza is likely to have been similar to countries where data were not available.

The study used results from more than two dozen research studies involving over 90,000 blood samples collected before, during and after the pandemic. The samples were tested for antibodies produced by the body in response to the specific flu strain.

Authors used previously published estimates of pandemic influenza mortality together with mortality estimates that are still in progress. This helped them to estimate the proportion of people infected who died from the pandemic virus.

Multiple exposures to previously circulating influenza viruses may have given older people some protection against the strain in 2009. Blood samples from before the pandemic showed that 14 percent of people aged 65 or over already had antibodies that reacted to the 2009 strain.

"This study is the result of a combined effort by more than 27 research groups worldwide, who all shared their data and experience with us to help improve our understanding of the impact the pandemic had globally," Dr Maria Van Kerkhove, from the Medical Research Council Centre for Outbreak Analysis and Modelling at Imperial College London, one of the lead authors of the study, said in a statement.

Dr. Anthony Mounts of the World Health Organization (WHO), the senior author of the paper, said that knowing the proportion of the population infected in different age groups, and those who died, will help public health decision-makers plan for and respond to pandemics.

"This information will be used to quantify severity and develop mathematical models to predict how flu outbreaks spread and what effect different interventions may have," Mounts said.

An expert from Queen Mary, University of London (QMUL), said that the numbers "make sense."

"It was the busiest virus on the block and it displaced other influenza viruses - it was the only virus in town," John Oxford, who was not a part of the study, told BBC News.