JOHN GREIM / SCIENCE PHOTO LIBRARY JOHN GREIM / SCIENCE PHOTO LIBRARY
Flu vaccine. A nurse injects an elderly woman in the upper arm with a vaccine against influenza. Influenza vaccines contain dead influenza viruses. When injected, these stimulate the body's immune system to produce antibodies that protect against future infection by live viruses. Vaccinations against influenza are usually short-lived and provide only a 60-70% success rate. This is because the viruses that cause influenza occasionally mutate into new forms that can overcome immunity to the parent strain. Nevertheless, vaccination is recommended for the elderly and anyone suffering from respiratory or circulatory disease.
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