2 Reasons Why H1N1 Sickens Young People

If you’ve been paying attention to the news, you may have heard Pandemic H1N1 is the primary flu virus circulating this season in San Diego and across the nation; the same strain that sickened millions of people all over the world in 2009.

You’ve probably also heard that Pandemic H1N1 affects young and middle-age adults more severely than other groups.

And you may be asking yourself, why?

The Centers for Disease Control and Prevention (CDC) continues to investigate why the H1N1 virus sickens more young people compared to children and older adults, who are typically hit hardest by other flu strains because of their weaker immune systems. But two factors play a part. One is that middle-age and younger adults have not been exposed to the H1N1 virus as much as older adults. 

Another reason is that young and middle-age adults have the lowest vaccination rate in the nation. (More on this in a moment.)

In 2009, the CDC conducted research that revealed adults older than 60 years of age had a level of immunity that was not present in children and younger adults when the H1N1 pandemic hit.

Further research has revealed that Pandemic H1N1, a new flu strain when it was discovered, has similar components to a previous H1N1 virus that was dominant during the 1950s and even earlier.

“Some element of immunity to Pandemic H1N1 is probable in older people because they had more exposure to these influenza viruses than younger groups,” said Wilma Wooten, M.D., M.P.H., County public health officer.

To date this season, there have been 29 flu-related deaths in San Diego County, compared to 32 at the same time last year, when the A H3N2 virus was dominant and 65 total flu deaths were reported. Nineteen of the flu deaths reported this season have occurred because of Pandemic H1N1.

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Five of the 29 deaths were people 49 years of age and younger. No pediatric deaths have been reported this year. Last flu season, 12 people under the age of 49 died, including two pediatric deaths.

A common occurrence every flu season is that practically all of the people who die have underlying medical conditions and most have no documented history of an influenza vaccine.

“Heart and respiratory disease, diabetes, HIV and other immune compromised illnesses, and even cancer are the types of conditions that contribute to someone dying from the flu,” Wooten said. “The great majority of healthy people who get the flu will recover on their own and not require medical attention.”

Regardless of your age, the best protection against any known strain of flu is getting vaccinated.

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Every year, the CDC and local health officials recommend that everyone 6 months and older get a flu vaccine, especially people who are at higher risk of developing serious complications from the flu, including people with certain medical conditions, pregnant women, and people 65 years and older.

But the message appears to be falling on deaf ears. Last flu season, only 41.5 percent of adults in the U.S. got a flu shot. CDC statistics from last November show that a mere 31 percent of people between 18 and 49 years old had gotten a flu shot.

“The fact that middle-age and young adults have less exposure to the H1N1 virus, coupled with a lower vaccination rate, increases their chances of severe illness,” Wooten said. 

This year, many more people are landing in the hospital. Of the 160 people who have required intensive care this flu season, 61 were 49 years old or younger and 39 of those got sick with Pandemic H1N1. Last flu season a total of 116 intensive care cases were reported.

“Getting vaccinated is the best way to prevent the flu and the current flu vaccines offer protection against Pandemic H1N1,” Wooten added. “If you have not done it, get your flu vaccination today. It takes about two weeks for immunity to develop, and flu season typically does not end until late March or early April.”

The vaccines, which also offer protection against Influenza A H3N2 and Influenza B strains, are available at doctors’ offices and retail pharmacies. If you don’t have medical insurance, you can go to a County public health center to get vaccinated. For a list of locations, visit or call 2-1-1.     


José A. Álvarez is a communications specialist with the County of San Diego Communications Office. Contact