Adults who aren’t current on their COVID-19 vaccine booster doses may have “relatively little remaining protection” against hospitalization compared to those who haven’t been vaccinated at all, suggests a new study from the Centers for Disease Control and Prevention (CDC).

The study spanned multiple states and examined more than 85,000 hospitalizations of people with “COVID-like illness.”

Dr. Shana Johnson, a physical medicine and rehabilitation physician in Scottsdale, Arizona, was not involved in the CDC study but reviewed its findings. 

The good news, Johnson said, is that the bivalent mRNA vaccine protects against the most severe COVID-19 outcomes, including hospitalization and critical disease (ICU admission and death), Johnson said.

The not-so-good news: The durability or duration of protection was not great, she noted.

“For adults, the vaccine effectiveness dropped from 62% at two months after vaccination to 24% at four to six months for protection against COVID-19 hospitalization,” Johnson said.

“Durability was better for preventing critical COVID-19 disease, at 50% at four to six months after vaccination.”

The vaccine was found to be effective for longer periods in people without immunocompromising conditions (weakened immune systems).

“These data support updated recommendations allowing additional optional bivalent COVID-19 vaccine doses for certain high-risk populations,” the CDC stated in a discussion of the study findings on its website.

“All eligible persons should stay up to date with recommended COVID-19 vaccines.” Despite the CDC’s September 2022 recommendation that all vaccinated people 12 years and older should receive a booster dose, the vast majority of Americans have not received it.