Swine flu pandemic of 2009 more deadly for younger adults, study finds

May 22, 2013, University of California, Irvine

As the world prepares for what may be the next pandemic strain of influenza virus, in the H7N9 bird flu, a new UC Irvine study reveals that the 2009 H1N1 swine flu pandemic was deadliest for people under the age of 65, while those 65 and over had greater immunity due to previous exposure to similar viruses.

Deaths from flu pandemics tend to skew younger than those from seasonal flu because of "antigenic recycling," or the fact that some parts of flu viruses have already made the rounds. Between 1918 and 1957, all in circulation fell into the H1N1 category, so in 2009, older adults had some protection stemming from their prior experience with viruses of this type, said Andrew Noymer, UC Irvine associate professor of public health and the study's co-author.

"The 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." The findings appear in the journal PLOS ONE.

The bulk of pneumonia and influenza deaths typically occur in people older than 65, but when H1N1 became the dominant flu strain in 2009, the accompanying rise in pneumonia and flu deaths took place within age groups that usually have low .

Overall, there were 53,692 pneumonia and influenza deaths in 2009, of which 2,438 were considered "excess," or above the number expected. In 2010, there were about 50,000 deaths from pneumonia and flu, of which 196 were considered excess.

Researchers obtained from the National Center for Health Statistics. Flu and pneumonia deaths between January 1959 and December 2010 were arranged by age, sex, month and underlying cause. Final numbers on flu deaths for 2009 and 2010 were released in 2012.

The 2009 pandemic was unusual not just for its excess fatalities but for the timing and age distribution of those deaths, Noymer said. October and November of that year saw the highest flu death rates in people 25 to 34 since at least 1959, when the computerized collection of population statistics began.

"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 suggests that public health officials consider targeting pandemic vaccination campaigns to adults under age 65, who are not at the greatest risk in regular, seasonal flu outbreaks.

The Centers for Disease Control & Prevention currently recommends annual influenza vaccinations for everyone over 6 months old, but pandemic vaccines may not be available in sufficient quantities for the whole population. Focusing on certain age groups may ensure the best use of a limited resource.

The novelty of the currently emerging bird , H7N9, is noteworthy, Noymer said, as the virus has not been seen before in anyone's lifetime. Although it's too early to predict the seriousness of H7N9, it does have the potential to be severe at all ages, since no one alive today has been previously exposed to this type of virus.

Explore further: Swine flu kills three in Central Europe

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.

Nobel laureate plays down flu pandemic scaremongering

May 21, 2013
A Nobel prize-winning scientist Tuesday played down "shock-horror scenarios" that a new virus strain will emerge with the potential to kill millions of people.

China reports fifth H7N9 bird flu death (Update 2)

April 4, 2013
A new strain of bird flu has claimed two more lives in China's business capital of Shanghai, taking the total number of human deaths attributed to the H7N9 virus to five, state media said Thursday.

Health officials: Worst of flu season may be over

February 8, 2013
Health officials say the worst of the flu season appears to be over.

H7N9 bird flu cases set to climb, but no pandemic: WHO

April 3, 2013
The number of cases of H7N9 bird flu in China looks set to climb as experts identify previously unexplained infections, but a lack of human-to-human transmission means a pandemic is not on the cards, the World Health Organisation ...

Computer model predicts when viruses become infectious

May 20, 2013
A new computer model could help scientists predict when a particular strain of avian influenza might become infectious from bird to human, according to a report to be published in the International Journal Data Mining and ...

Recommended for you

Tibetan sheep highly susceptible to human plague, originates from marmots

August 16, 2018
In the Qinghai-Tibet plateau, one of the region's highest risk areas for human plague, Himalayan marmots are the primary carriers of the infectious bacterium Y. pestis. Y. pestis infection can be transmitted to humans and ...

Autoimmunity plays role in development of COPD, study finds

August 16, 2018
Autoimmunity plays a role in the development of chronic obstructive pulmonary disease (COPD), according to a study led by Georgia State University and Vanderbilt University Medical Center that analyzed human genome information ...

Reliable point-of-care blood test can help prevent toxoplasmosis

August 16, 2018
A recent study, performed in Chicago and Rabat, Morocco, found that a novel finger-prick test for infection with the parasite Toxoplasma gondii during pregnancy—and many other potential applications—is 100 percent sensitive ...

Scientists identify nearly 200 potential tuberculosis drug targets

August 16, 2018
Tuberculosis is one of the top 10 causes of death worldwide. Nearly 2 million people die every year from this infectious disease, and an estimated 2 billion people are chronically infected. The only vaccine, developed almost ...

First mouse model to mimic lung disease could speed discovery of more effective treatments

August 16, 2018
The biggest hurdle to finding effective therapies for idiopathic pulmonary fibrosis (IPF) – a life-threatening condition in which the lungs become scarred and breathing is increasingly difficult – has been the inability ...

Anticancer drug offers potential alternative to transplant for patients with liver failure

August 15, 2018
Patients suffering sudden liver failure could in the future benefit from a new treatment that could reduce the need for transplants, research published today shows.

0 comments

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.