Two vaccines are currently approved by the Food and Drug Administration (FDA) to prevent shingles.
Zostavax is a live virus vaccine which has been available since 2006 and prevents shingles about 50% of the time, though it is less effective the older a person is when they receive it. Shingrix, which was approved by the FDA in 2017, is not a live virus, but has an additive in the vaccine to boost immune response. It is about 97% effective at preventing shingles regardless of a person's age and so far has been effective for at least 4 years after vaccination.
Because Zostavax has live virus in it, giving a "challenge" dose of Zostavax - vOka varicella zoster virus - to people who have received both vaccines (Zostavax or Shingrix) in the past, will allow researchers to learn more about how the body works to prevent shingles and how any shingles vaccination helps protect against shingles.