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The two-dose recombinant zoster vaccine (RZV; Shingrix) remained highly effective at preventing shingles over a 4-year period in real-world settings, according to a prospective cohort study.

Over 4 years, the two-dose regimen was 76% effective (95% CI 75-78), with one dose of the vaccine just 64% effective over the same time period (95% CI 62-67), underscoring the need for people to get both doses, Nicola P. Klein, MD, PhD, of Kaiser Permanente Northern California in Oakland, and colleagues reported in the .

"The study findings are reassuring in confirming that the recombinant zoster vaccine is highly effective for at least 4 years," Klein told MedPage Today in an email. "The study also reaffirms the importance of getting the second dose of vaccine to maximize protection against shingles, which can be a painful and potentially dangerous condition."

Klein noted that vaccine effectiveness was the same in patients who received the second vaccine dose later than the recommended interval of 2 to 6 months between doses. "One of the main messages is that everyone for whom the vaccine is should get two doses, but not to panic if the second dose ended up being delayed beyond 6 months."

The study included about 2 million people over the age of 50 who had never received RZV. During the study period from 2018 through 2022, 38% received at least one vaccine dose and 29% received two doses of RZV. After both doses, vaccine effectiveness was 79% during the first year, 75% during the second year, and 73% during the third and fourth years.

Although vaccine effectiveness after one dose was 70% effective during the first year, effectiveness waned substantially after that to 45% during the second year, 48% during the third year, and 52% after the third year.

Effectiveness also varied by age. The vaccine was slightly more effective in people who were vaccinated when they were younger than 65 years of age (81%) versus those who were older (74%).

Notably, in people who received corticosteroids -- a group at significantly higher risk for shingles -- the vaccine exhibited lower but substantial effectiveness (65%). The authors pointed out the number of shingles cases per 100 recipients prevented by the vaccine was about the same in corticosteroid users and nonusers.

"Our analysis can give clinicians additional support for urging adults in the recommended categories -- over age 50 or immunocompromised -- to get vaccinated against herpes zoster," Klein said.

The study's estimates of vaccine effectiveness were lower than those observed in the and the clinical trials, the authors noted. ZOE-50 found that the vaccine was 97% effective in people ages 50 and older and ZOE-70 found that the vaccine was 90% effective in those 70 years of age or older. A long-term follow-up study of those trials concluded that vaccine effectiveness held steady for at least 7 years, but long-term effectiveness of the vaccine in real-world settings hasn't been extensively evaluated, the authors said.

The prospective cohort study gathered data from patients in four healthcare systems within the Vaccine Safety Datalink, a collaboration between the CDC and nine integrated healthcare systems. RZV was offered free of charge to most eligible patients. Researchers excluded those who received a diagnosis of shingles in the year before the study began. Among participants, 38% were 65 years of age or older, 53% were female, and 59% were white. The outcome was incident herpes zoster infection.

During the study follow-up over 45,000 cases of shingles were diagnosed and most (94%) were in unvaccinated participants. Unadjusted incidence of herpes zoster was 1.7 per 1,000 person-years in fully vaccinated people versus 6.7 per 1,000 person-years in unvaccinated people.

One of the potential limitations of the study was that a diagnosis of shingles required both a herpes zoster diagnosis ICD code and an antiviral prescription, rather than PCR testing. This may have lowered vaccine effectiveness estimates, researchers wrote. Also, patients with milder illness may have not sought care, potentially overestimating vaccine effectiveness.

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