Researchers for a study conducted by UC Irvine reveal that the 2009 H1N1 was deadliest for people below the age of 65 as the older generation already had some immunity against it.
With news of a new pandemic strain of influenza virus H7N9 bird flu making headlines, more scientists are investing on studies on similar viruses.
A recent study conducted by researchers from the University of California, Irvine, revealed that the 2009 H1N1 was deadliest for people below the age of 65 as people above 65 had already become immune to the virus owing to prior exposure to similar viruses.
Andrew Noymer, UC Irvine associate professor of public health and the study's co-author said that from 1918 to 1957 all viruses fell into the H1N1 category so by 2009, when the 2009 H1N1 swine flu broke out, most older people were already protected from the virus because they had previously experienced such types of viruses.
"The swine flu pandemic was relatively mild in the extent to which flu-related deaths were above normal, seasonal levels," he said. "Excess death rates were highest among 25- to 64-year-olds."
Typically, most deaths caused by pneumonia and influenza are among adults over the age of 65. But after the 2009 H1N1 swine flu, the accompanying rise in pneumonia and flu deaths took place within age groups that usually have low mortality rates.
"The pandemic definition is based on the novelty of the virus strain and on deaths, but mortality does not need to be enormous for it to be considered a pandemic," he said. "The 2009 swine flu was an excellent example of a virus strain with relatively lenient mortality."
Noymer concluded that the H7N9 bird flu is of a different type of virus that hasn't been seen before. He says that though it is early to predict the seriousness of H7N9, it will definitely affect all age groups alike since no one has been exposed to the virus previously.
The findings appear in the journal PLOS ONE.
