New Swine Flu Death Estimate Much Higher

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Harvard Medical School
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New Swine Flu Death Estimate Much Higher

News Review From Harvard Medical School

November 27, 2013

News Review From Harvard Medical School -- New Swine Flu Death Estimate Much Higher

The H1N1 "swine flu" pandemic of 2009 killed about 11 times as many people as previously reported, a new study finds. The World Health Organization (WHO) had said there were 18,500 deaths. But this included only people whose infection with H1N1 was confirmed by a laboratory. Many other flu deaths may not have been confirmed. The new study involved 60 researchers in 26 countries. They looked at numbers for virus activity and deaths caused by respiratory illness in 20 countries. These countries totaled more than one-third of the world's population. They found that these deaths were far above normal in 2009. They also were much more likely than usual to occur among young adults. H1N1 tended to cause the most severe illness among younger people. Based on these numbers, the researchers estimated that H1N1 caused 123,000 to 203,000 deaths worldwide. Death rates were much higher in North and South America than in Europe. The journal PLoS Medicine published the study. HealthDay News wrote about it November 26.


By Howard LeWine, M.D.
Harvard Medical School


What Is the Doctor's Reaction?

Some have thought that the H1N1 "swine flu" epidemic of 2009 did not live up to the hype. Not so. Deaths from the flu virus were 10 times higher than originally reported, researchers report. The conclusion is based on a new analysis of data. The journal PLoS Medicine published the study results.

The official worldwide number of deaths from the H1N1 virus was 18,631. That's the number of deaths reported by the World Health Organization (WHO). But this new study says that 123,000 to 203,000 deaths occurred from lung infections during the last 9 months of 2009. The WHO has acknowledged that the number of deaths had to be higher than the official count. The WHO only used deaths in which a laboratory had confirmed an H1N1 influenza infection.

This most recent analysis might overestimate the number of deaths caused by swine flu in 2009. But it's probably not off by much. Here's why.

The number of deaths from lung infections during the last 9 months of 2009 was much higher than in other years. And the deaths happened in younger people. About 75% of those who died from H1N1 infection were under age 65.

This is not what is expected during most flu seasons. Usually flu kills the most vulnerable -- the elderly and those with chronic illness.  

But with the 2009 H1N1 virus, younger people had a higher risk of complications.

First, no virus similar to this one had circled the globe in more than 60 years. So those under the age of 65 had virtually no immunity against this strain.

Second, younger people have stronger immune systems. At first, this might not make sense as a reason for their higher risk of problems with H1N1. If they have stronger immune systems, shouldn't they be able to fight off the virus more easily?

The problem is that sometimes the immune system overreacts. In rare cases, the immune system goes wild. It can cause widespread inflammation and organ damage throughout the body in an attempt to fight off the virus.


What Changes Can I Make Now?

This new study is a good reminder of why it's so important to get the flu vaccine every year.

Everyone age 6 months and older should get the vaccine. This is especially true if you or someone you know is more likely to have severe health problems caused by flu. These groups include:

  • Children younger than 5
  • Pregnant women and women who are trying to get pregnant
  • Adults 65 and older
  • People under age 20 who take aspirin regularly
  • People with heart disease, especially if they have had a heart attack or a hospital stay for angina in the last year.
  • People with asthma, emphysema, chronic bronchitis or other lung disease
  • People with any condition that can weaken the immune system, including diabetes
  • People with severe obesity, a body mass index of 40 or higher

You also should get vaccinated if you are in regular contact with anyone at high risk of severe illness caused by flu. This is especially true if you have or care for a child too young to be vaccinated.

Plenty of flu vaccine is available this season.  And, for the first time, you can get a vaccine not made from eggs. That means people with egg allergies can get vaccinated.


What Can I Expect Looking to the Future?

New flu strains will continue to arise. That's why you need a vaccine every year. The vaccine changes each year based on what strains are likely to emerge.

Scientists are getting better at predicting what the coming flu strains will look like. But surprises such as the H1N1 strain in 2009 will happen. Fortunately, they should be rare events.


Last updated November 27, 2013

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