What is an inactivated (killed) vaccine?

An inactivated vaccine is one that is made from dead viruses or bacteria, or may be made from pieces of them (so-called fractional vaccines). They are killed with heat, radiation or chemicals. They are unable to cause disease, but still able to provoke a response from the immune system. Afterward, the immune system's memory cells will recognize the disease and attack it if it invades the body. They are not as effective as live vaccines, however, and usually require multiple shots. Common inactivated vaccines include those for polio and hepatitis A.

An inactivated vaccine is a killed virus. The virus particles are grown in culture and then killed with heat or formaldehyde. The flu and polio vaccines are examples of inactivated vaccines. These compare to live vaccines, such as measles, mumps and rubella.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.