At least one in five were infected in flu pandemic, international study suggests

January 25, 2013
At least one in five were infected in flu pandemic, international study suggests

(Medical Xpress)—At least one in five people in countries for which data are available were infected with influenza during the first year of the 2009 H1N1 pandemic, according to a new study.

The highest rates of infection were in children, with 47 per cent of those aged five to 19 showing signs of having caught the virus. Older people were affected less, with only 11 per cent of people aged 65 or older becoming infected.

The findings come from an led by the and Imperial College London, which analysed data from 19 countries, including the UK, US, China and India, to assess the global impact of the 2009 .

The results, published in the journal Influenza and Other , showed that 20-27 per cent of people studied were infected in the pandemic during the first year of circulation. The researchers believe the incidence of influenza is likely to have been similar in countries where data were not available, meaning that as many as a quarter of the world's population may have been infected.

The study collated results from more than two dozen research studies involving more than 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 that caused the pandemic.

While this study did not set out to look at mortality, the authors also used previously published estimates of mortality together with that are still in progress, to estimate the proportion of people infected who died from the pandemic virus. Based on an estimate of approximately 200,000 deaths, they suggest that the case fatality ratio was less than 0.02 per cent.

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

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: "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 Anthony Mounts of the World Health Organization, the senior author, said: "Knowing the proportion of the population infected in different age groups and the proportion of those infected 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."

Explore further: 2009 H1N1 pandemic flu more damaging to lungs, opens opportunities for bacterial infection

More information: Van Kerkhove et al. (2012) Estimating age-specific cumulative incidence for the 2009 influenza pandemic: a meta-analysis of A(H1N1)pdm09 serological studies from 19 countries. Influenza and Other Respiratory Viruses DOI: 10.1111/irv.12074 ,

Related Stories

Swine flu kills three in Central Europe

January 24, 2013

Three people have died in Romania and Macedonia after being infected with the H1N1 influenza strain known as swine flu, the two countries' health ministries said Thursday.

Recommended for you

Monkeys in Asia harbor virus from humans, other species

November 19, 2015

When it comes to spreading viruses, bats are thought to be among the worst. Now a new study of nearly 900 nonhuman primates in Bangladesh and Cambodia shows that macaques harbor more diverse astroviruses, which can cause ...

One-step test for hepatitis C virus infection developed

November 14, 2015

UC Irvine Health researchers have developed a cost-effective one-step test that screens, detects and confirms hepatitis C virus (HCV) infections. Dr. Ke-Qin Hu, director of hepatology services, will present findings at the ...

Computer model reveals deadly route of Ebola outbreak

November 10, 2015

Using a novel statistical model, a research team led by Columbia University's Mailman School of Public Health mapped the spread of the 2014-2015 Ebola outbreak in Sierra Leone, providing the most detailed picture to date ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.