LONDON: The 2009 global H5N1 swine flu pandemic - the first in over 41 years that swept throughout the globe in record time -- infected at least one in five Indians with the highest rates of infection being among children.
A joint Imperial College, London, and the World Health Organization global study released on Saturday found that 47% of those aged five to 19 showed signs of having caught the deadly influenza virus in India.
Older people were affected less, with only 11% of people aged 65 or above becoming infected.
The study analyzed data from 19 countries, including India, UK, US and China, to assess the global impact of the 2009 pandemic.
It collated results from over two dozen research studies involving more than 90,000 blood samples collected before, during and after the pandemic and showed that the virus that continues to infect and kill Indians now affected 20-27% people studied during the first year of the pandemic.
The study was published in "Influenza and Other Respiratory Viruses" journal on January 26.
Imperial College's Dr Maria Van Kerkhove said, "This study is the result of a combined effort by more than 27 research groups worldwide, who all shared their data with us to help improve our understanding of the impact the pandemic had globally.'' She said the samples were tested for antibodies produced in response to the specific flu strain that caused the pandemic.
While this study did not set out to look at mortality, the authors also used previously published estimates of pandemic influenza mortality together with mortality estimates 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%.
The study said multiple exposures to previously circulating influenza viruses may have given older people some protection against the strain.
Blood samples from before the pandemic showed that 14% people aged 65 or above had antibodies that reacted to the 2009 strain.
WHO's Dr Anthony Mounts 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.'' He said 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."
The study said data used to estimate age-specific incidence were available from 11 countries and 12 studies. ``The overall incidence of H1N1 was 24% and varied significantly by age. The highest age-specific incidence was found among children 5-19 years old (46%) followed by 0-4 years old (37%) and decreased by age from 20 years old and older (20-44 years old 20% and 14% among 45-64 years olds). Overall incidence was 28% lower in Asia when compared with Europe."
The WHO in August 2009 issued the swine flu alert to the highest pandemic level, signaling that a global epidemic of the H1N1 virus had begun. It first detected the novel pandemic influenza H1N1 virus in Mexico and the US in April 2009.
The last flu pandemic was declared in 1968 when H3N1 virus strain killed an estimated 1 million people.
The US Centres for Disease Control and Prevention (CDC), Atlanta, recently said India may have grossly underestimated the might of 21st century's most aggressive pandemic.
A recent CDC study, with help from New Delhi's All India Institute of Medical Sciences, published in medical journal Lancet said the deaths caused by H1N1 pandemic flu in its first year (2009-10) could be 15 times higher than the number of laboratory-confirmed deaths previously reported to the WHO.
During the pandemic, 18,500 laboratory-confirmed H1N1-deaths were reported worldwide from April 2009 to August 2010.
The CDC research indicated that the death toll was anywhere between 1.51 lakh and 5.75 lakh during the first year when the virus circulated worldwide.
The results said that 80% deaths occurred in people younger than 65, contrary to seasonal influenza where most deaths occur among the elderly.
Additionally, the study suggested that 51% deaths may have occurred in south-east Asia and Africa home to 38% of the world's population.
"China and India, where about a third of the world's population live have garnered little information about the burden of influenza," it said.
India's age-adjusted respiratory and cardiovascular mortality rate associated with 2009 pandemic influenza H1N1 per 100 000 individuals stood at 4.1-6 per 100,000 population.
"An additional 83,300 cardiovascular deaths associated with the 2009 pandemic influenza were estimated to have occurred in people older than 17 years globally, resulting in a total of 284,400 respiratory and cardiovascular deaths. Around 20% of these deaths occurred in people older than 64 years," the CDC study said.
Swine flu pandemic infected at least one in five Indians: Study
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Swine flu pandemic infected at least one in five Indians: Study
