Data gathered from 19 different countries reveals that the global swine flu pandemic which began in 2009 infected close to 20% of the population and almost 50% of all schoolchildren. The virus which originated in Mexico is thought to have killed close to 200,000.
Swine flu is a respiratory disease commonly found in pigs – around 1 to 4 percent of pigs that develop the disease die from it. It is caused by a highly contagious strain of Influenza A virus and it’s spread by direct and indirect contact with pigs.
Swine flu is usually of the H1N1 subtype, although there are also other types which are less common, such as H3N1, H3N2, and H1N2. The subtype that infected humans in 2009 was H1N1.
The study was conducted by a team of international researchers led by the World Health Organization and aimed to further understand the global impact of the H1N1 virus. The researchers used data from published and unpublished H1N1pdm seroepidemiological studies to evaluate the true extent of the pandemic.
The countries from which data was gathered included: Australia, Canada, China, Finland, France, Germany, Hong Kong SAR, India, Iran, Italy, Japan, Netherlands, New Zealand, Norway, Reunion Island, Singapore, United Kingdom, United States, and Vietnam.
Antibodies in blood samples reveal true rate of infection among population
They analyzed around 90,000 blood samples to identify cross-reactive antibodies to the H1N1pdm virus and determine the rates of H1N1pdm infection. The antibodies are produced when the body is infected with the virus. Hence, by comparing the prevalence of people with the antibodies before and after, the researchers were able to estimate the number of people who were infected
Although the mortality rate of the virus is only 2 in every 10,000 people infected, the researchers highlight that the virus infected children in a much more rampant way than the typical seasonal flu. The “swine flu” virus infected 47% of people aged five to nineteen, compared to only 11 percent of those over the age of 65. Even though it is incredibly infectious, it should be noted that according to scientists at the National Institute of Allergy and Infectious Diseases, around 59% of the U.S. population (around 183 million people) are immune to the virus.
Even though the World Health Organization confirmed 18,500 deaths related to the H1N1 virus, a recent report published in The Lancet estimates that the swine flu death toll might have actually reached something around the 280,000 mark. Based on an estimate of 200,000 deaths, the fatality ratio is less than 0.02 percent.
The authors concluded:
“Our results offer unique insight into the global impact of the H1N1 pandemic and highlight the need for standardization of seroepidemiological studies and for their inclusion in pre-pandemic preparedness plans. Our results taken together with recent global pandemic respiratory-associated mortality estimates suggest that the case fatality ratio of the pandemic virus was approximately 0·02%.”