killedvirus

A killed virus, or inactivated virus, is a virus whose ability to replicate has been destroyed through chemical or physical treatment while its structural proteins remain largely intact. Because it cannot reproduce, such viruses cannot cause disease by infection, but their components can still be recognized by the immune system to induce immunity.

Inactivation methods include chemical agents such as formaldehyde or beta-propiolactone, and physical methods such as heat or irradiation. After inactivation, the material is tested to ensure no residual infectivity. Inactivated vaccines rely on presenting viral antigens to the immune system rather than generating infection; they primarily stimulate humoral (antibody) responses and often require adjuvants and booster doses to achieve robust and lasting immunity. Storage requirements tend to be less stringent than for live vaccines, but they must be kept within specified temperatures to preserve antigenicity.

Killed-virus vaccines have a long history, including the first poliovirus vaccine (inactivated by formaldehyde) and many influenza vaccines. They are generally considered safe for a broad population, including some immunocompromised individuals, though they can elicit weaker immunity than live attenuated vaccines. Drawbacks include potentially lower or shorter-lived immunity and the need for adjuvants or multiple doses. Examples include the inactivated polio vaccine (IPV), hepatitis A vaccine, influenza vaccines, rabies vaccines, and some COVID-19 vaccines (inactivated formulations).