Varicella zoster virus
Varicella zoster virus (VZV) belongs to the herpesvirus family, and is also named human herpesvirus-3 (HHV-3). VZV causes two clinically distinct diseases: varicella (aka chickenpox) and herpes zoster (aka shingles).
VZV is highly contagious—it spreads from person to person via airborne and direct contact transmission. Chickenpox results from primary VZV infection whereas shingles results from reactivation of latent VZV. This distinction is nuanced. For instance, a person who has never been exposed to VZV (i.e., no prior chickenpox or vaccination) is at risk for chickenpox but not at risk for shingles. If such a person comes in direct contact with someone who has shingles, then VZV transmission would manifest as chickenpox—not shingles—in the susceptible person.
Chickenpox vaccination
There are 2 chickenpox vaccines available on the US market: varicella vaccine (VAR; aka Varivax) and a combination measles, mumps, rubella, and varicella vaccine (MMRV; aka ProQuad). Both Varivax and ProQuad are live vaccines containing attenuated VZV. Varivax is approved for people 12 months of age and older (including adults); ProQuad is approved for 12 months through 12 years of age.
We typically give Varivax (in addition to MMR) at the 1yo well visit and ProQuad at the 4yo well visit. Here’s why: Compared with use of MMR vaccine and varicella vaccine at the same visit, use of the MMRV vaccine results in one fewer injection but is associated with a higher risk for fever and febrile seizures 5-12 days after the first dose among children aged 12-23 months (approximately one extra febrile seizure for every ~2,300 doses of MMRV vaccine); use of the MMR vaccine and varicella vaccine avoids this increased risk in these patients.
Serologic studies indicate that 99% of people born before 1980 have had chickenpox even though many cannot recall the disease. As a result, there is no need to ask about a history of chickenpox or perform serologic testing in these patients so long as they are immunocompetent. For immunocompromised adults, evidence of immunity requires either documentation of 2 doses of varicella vaccine, serologic evidence of immunity, or a history of chickenpox or shingles diagnosed by a healthcare provider.
Otherwise we should vaccinate susceptible older children and adults whenever the opportunity arises. Because the chance of being exposed to chickenpox in the US is low, unvaccinated older children and adults who have not had chickenpox now have a greater chance of remaining susceptible for longer. These older individuals, when they contract chickenpox, are more likely to become seriously ill and develop complications in comparison to younger children.
Shingles vaccination
There is only 1 shingles vaccine on the US market: recombinant zoster vaccine (RZV; aka Shingrix). Shingrix contains a lone protein isolated from the shell of VZV; it does not contain live VZV. Shingrix was studied in immunocompetent adults in 2 pre-licensure clinical trials; efficacy against shingles was 97% for people 50-59 years of age, 97% for 60-69 years, and 91% for 70 years and older (these numbers are remarkable—no other vaccine is so effective in older patients). Shingrix is a 2-dose series approved for patients 50 years and older as well as adults 19 years and older who are (or will be) immunodeficient or immunosuppressed because of disease or therapy. Last, it should be noted that Shingrix has not been evaluated for the prevention of primary infection with VZV.
Previously, there was another shingles vaccine on the US market from 2006 to 2020 called zoster vaccine live (ZVL; aka Zostavax). It was found to have inferior efficacy in comparison to Shingrix, so much so that patients who previously received Zostavax should still receive 2 doses of Shingrix.