The effectiveness of a third booster dose of a COVID-19 vaccine declines after four months, the Centers for Disease Control and Prevention (CDC) reported, citing real-world data from 10 states.

During a recent five-month period marked by the surging Omicron variant, vaccine efficacy against COVID-19-related hospitalizations was 91 percent two months following a third booster shot, the CDC said.

But that number fell to 78 percent four months after receiving a third booster dose, based on the real-world data from 93,000 hospitalizations and 241,000 emergency room visits from late September 2021 to early February 2022.

The CDC noted that only 10 percent of individuals in the study had received booster doses.