How do the monkeypox vaccines work?

Infectious Diseases Vaccines

The JYNNEOS vaccine is a live, attenuated FDA-approved vaccine for the prevention of monkeypox and smallpox. This means that the vaccine contains a weakened version of the vaccinia virus, a virus very similar to monkeypox and smallpox. This weakened virus cannot make copies of itself or spread. The body recognizes the virus and makes antibodies that also fight against smallpox and monkeypox.

ACAM2000 is a live, replicating virus vaccine also made from the vaccinia virus that can be used to protect against monkeypox and smallpox. Because this vaccine contains virus that can make copies, it is not given to people who have weakened immune systems.

The JYNNEOS vaccine is made from a live but weakened form of the vaccinia virus. Vaccinia is a type of poxvirus that is closely related to smallpox and monkeypox. (And yes, you read that right. It is called vaccinia, like vaccine. This is the virus used in vaccines during smallpox eradication!). The vaccinia virus is altered so that it is weaker, cannot make copies of itself, or spread. The body recognizes the virus and kicks off an immune response. B-lymphocytes (or B-cells) are white blood cells that make antibodies. Because vaccinia is so similar to monkeypox, those antibodies also recognize the monkeypox virus! T lymphocytes (or T cells) can help the B cells make antibodies and kill off infected cells. Some B cells and T cells hang out to “remember” what the virus looks like, so that if the body ever gets exposed to it again, the immune system is ready to go and prevent infection and illness.

Because the virus in the JYNNEOS vaccine cannot make copies of itself, it is safe to give for people who have weakened immune systems (like folks with HIV or people who take medications that can weaken the immune system). In fact, it was originally developed to be given to immunocompromised people in the event of a smallpox bioterrorism attack. The other smallpox vaccine, called ACAM2000, is a replicating live vaccinia virus vaccine (this virus can make copies of itself) and is not given to folks with weakened immune systems. ACAM2000 is administered by pricking the skin and introducing the virus. A lesion (or sore) will develop at the site of vaccination and has virus growing inside of it. The body has an immune response and makes antibodies against vaccinia virus that also protect against smallpox and monkeypox. However, because there is live virus in that sore, the virus can spread to other people. People who get ACAM2000 must take precautions for 28 days or more to prevent spread to individuals who would be at high risk of infection. After ACAM2000 vaccination, people should avoid folks who are immunocompromised, have eczema, are pregnant, or are kids less than 12 months old.

People who have had contact with someone who has monkeypox, had a sexual partner in the past 2 weeks diagnosed with monkeypox, had sex with multiple partners in the past 2 weeks in an area with monkeypox transmission, or whose jobs expose them to monkeypox are currently eligible for vaccination. Talk with your healthcare provider about vaccination.

Stay safe. Stay well. Stay impressed with how cool vaccines are.
Those Nerdy Girls

Additional Links:

FDA: Key Facts About Vaccines to Prevent Monkeypox Disease