How long (one season or more) will immunity be effective from the H1N1 vaccine? Will this be an annual vaccine like the seasonal flu?

Influenza (flu) viruses change from year to year. You are unlikely to get infected with the same exact strain of influenza (flu) more than once. Most people with flu-like illness since spring 2009 don't know whether they were infected with 2009 H1N1 or another flu virus strain. If you think you had 2009 H1N1 infection, ask your doctor if you should be vaccinated. The only sure way to diagnose 2009 H1N1 infection is with real-time reverse transcription-polymerase chain reaction (RT-PCR).

Even if you had a confirmed case of 2009 H1N1 flu, you can still get infected with other flu strains. You should make sure you get the seasonal flu vaccine. If you had a flu-like illness since spring 2009 that wasn't diagnosed as 2009 H1N1 flu by RT-PCR, get the H1N1 and seasonal flu vaccines.

Also, a vaccine made against flu viruses circulating last year may not protect against the newer viruses. That is why the influenza vaccine is updated every year to include current viruses.

Last Reviewed: 01/05/2012

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