Search Here

More than a fifth of the world's population, including half of children, was infected with the H1N1 virus during the first year of the pandemic in 2009, according to a new study published on Friday.

Official statistics estimate that the H1N1 virus killed around 20,000 people worldwide. The virus or swine flu first appeared in Mexico in 2009 and rapidly spread worldwide.

The latest findings published in the journal Influenza and Other Respiratory Viruses confirm warnings that the H1N1 virus or swine flu was highly contagious and that the original estimates of the flu's destructiveness were underestimated.

Researchers found that overall, between 20 and 27 percent of people were infected by the swine flu virus.

The latest study led by the World Health Organization found that the highest infection rates were among children, with 47 percent of those between the ages of five and 19 showing signs of infection. Researchers found that older people were not as affected by swine flu, with only 11 percent people aged 65 or older becoming infected.

Scientists collected results from more than two dozen research studies that involved more than 90,000 blood samples collected before, during and after the pandemic to look for evidence of the body's immune system fighting the H1N1 virus.

Researchers had tested the blood samples for antibodies that were produced in response to the H1N1 flu strain.  By comparing the results before and during the pandemic, scientists were able to determine how many people were infected as the virus spread around the world.

Researchers found that while a large percentage of people had been infected, not all of them developed full-blown flu.

Specifically, around 24 percent of people had been infected overall, which included half of children between the ages of five and 19.

However, based on the findings, researchers estimate that less than 0.02 percent or two in every 10,000 people died during the pandemic.

"However, those that did die are much younger than in seasonal flu so the years of life lost will be much more," researcher Dr. Maria Van Kerkhove from Imperial College London told BBC.

"The figures drive home how incredibly infectious the virus is," Kerkhove said.

Experts explained that the reason why fewer older people, who tend to die during outbreaks, died during the H1N1 epidemic was because they had been exposed to the virus decades before.

"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," senior study author Dr. Anthony Mounts of the World Health Organization said in a statement.

"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," he added.