Astronauts are often required to get immunizations (incorrectly called vaccines). Which ones are required?
The full list of immunizations required upon selection is not provided to the public, however we employ something called the Flight Crew Health Stabilization Program to limit uphill transmission of infectious diseases to the ISS - this may be public, I’ll check. The HSP involves confirming not only the crew’s vaccination status, but also those supporting launch operations who will have direct contact with the crew. Those supporting launch who can not obtain required vaccinations are required to don personal protective equipment to reduce the risk to crew. This is all combined with a short period of crew quarantine prior to launch, so that any viral incubation has time to manifest, and crew to recover prior to visiting their colleagues on ISS.
Uphill transmission of viral illness is a significant concern, and ongoing research suggests some degree of immune suppression/dysfunction accompanies long-duration spaceflight; this means the efficacy of those immunizations once crew are on orbit is unknown, and the operational impact of even a common cold virus making its way to ISS could be significant.
The old version of the HSP circa 2010 is public and available here: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20130000048.pdf
The current version is not publicly available. The above version focuses solely on the seasonal flu vaccine requirements, and leaves vague the full list required for both crew and direct contacts during the pre-launch quarantine period.