Booster Efficacy Wanes After 4 Months, Still Protects Against Severe COVID-19

Just as a primary COVID-19 vaccine series wanes over time, the booster doses also decrease in efficacy. This week, the US Centers for Disease Control and Prevention (CDC) reported that though a Pfizer-BioNTech or Moderna booster doses increase vaccine efficacy, their protection wanes even faster than initial vaccination.

In their Morbidity and Mortality Weekly Report (MMRR), the CDC published a study that found the effectiveness of booster doses wanes significantly after 4 months.

Conducted during the period when the highly transmissible Omicron was the dominant COVID-19 variant, the study found that in the first 2 months after a third booster dose, recipients had an 91% reduced risk of hospitalization. By the fourth month after boosting, vaccine protection against hospitalization had dipped to 78%.

The test-negative case-control study utilized data from 8 VISION Network sites, analyzing vaccine effectiveness against COVID-19 emergency department/urgent care (ED/UC) visits and hospitalizations among adults 18 years and older. The VISION Network data encompassed 241204 ED/UC encounters and 93408 hospitalizations across 10 US states from August 26, 2021-January 22, 2022, representing several points in time after receipt of a second or third vaccine dose during both Delta and Omicron variant predominance.

During both the Delta and Omicron periods, antibody levels were higher after a third dose than after a second, but vaccine protection waned more rapidly during the Omicron period. Vaccine efficacy for participants who received 2 or 3 doses was lower during the Omicron period than during the Delta period.

During Omicron, vaccine efficacy against ED/UC visits was 87% during the first 2 months after a booster dose and decreased to 66% 4-5 months after vaccination. Protection against hospitalizations was 91% in the first 2 months after boosting, dipping to 78% 4 or more months after receiving the third dose.

Waning vaccines have become a major concern, especially as Omicron continues to cause breakthrough infections. However, the investigators found boosters do raise antibodies enough to provide lasting protection against severe COVID-19 disease, hospitalization, and death. The study authors wrote, “All eligible persons should remain up to date with recommended COVID-19 vaccinations to best protect against COVID-19–associated hospitalizations and ED/UC visits.”

The CDC currently recommends all persons 12 and older receive an mRNA booster vaccine:

• 6 months after initial vaccination for Moderna (mRNA-1273) recipients
• 5 months after initial vaccination for Pfizer-BioNTech (BNT162b)
• 2 months after initial vaccination for Janssen (Johnson & Johnson; Ad26.COV2.S) recipients

Both mRNA vaccines are currently preferred over the Janssen vaccine, as boosters and as a primary series, though vaccination with Janssen is recommended if no other COVID-19 vaccine is available