A Morbidity and Mortality Weekly Report (MMWR) published by the Centers for Disease Control and Prevention on May 26 indicates that adults who have received primary COVID-19 vaccination but not received a bivalent mRNA booster vaccine have little remaining protection against COVID-19–associated hospitalization compared with those who are unvaccinated.
However, those who have only received primary vaccination may have more remaining protection against critical illness than those who are unvaccinated.
Bivalent booster vaccine effectiveness (VE) against COVID-19–associated hospitalization declines from 62 percent in the period seven to 59 days following vaccination to 24 percent after 120 to 179 days.
Researchers found that bivalent booster VE was even lower in immunocompromised adults.
Just one in five adults has received a bivalent booster dose as of May 10, and the agency urges adults to stay up to date with recommended COVID-19 vaccines.
In another study published June 2, researchers estimate that, by the third quarter of 2022, nearly half of Americans ages 16 and older had hybrid immunity derived from both previous infection and vaccination, against SARS-CoV-2, the virus that causes COVID-19.
Hybrid immunity wanes more slowly and provides better protection compared with infection or vaccination alone. The agency says hybrid immunity likely is contributing to lower rates of severe disease and death from COVID-19 from 2022 to 2023 compared with earlier in the pandemic.
Researchers assessed a nationwide longitudinal cohort of blood donors to estimate the incidence of infection and the prevalence of infection- or vaccination-induced antibodies.
Visit the America’s Essential Hospitals coronavirus resource page for more information about the pandemic.
Contact Senior Director of Policy Erin O’Malley at eomalley@essentialhospitals.org or 202.585.0127 with questions.
