Omicron boosters can provide additional protection against newly dominant COVID variants such as XBB and XBB.1.5 for at least three months, the Centers for Disease Control and Prevention (CDC) said Wednesday, citing a study.

In September, the U.S. rolled out mRNA based COVID shots developed by Pfizer (NYSE:PFE)/BioNTech (NASDAQ:BNTX) and Moderna (NASDAQ:MRNA) as boosters targeting Omicron BA.4 and BA.5 subvariants.

However, as of Jan. 21, Omicron BA.2 sublineages, XBB and XBB.1.5 accounted for an estimated 52% of COVID cases in the country.

The CDC study was designed to evaluate the vaccine effectiveness of updated boosters against BA.5 and XBB/XBB.1.5-related virus strains in adults who had previously received 2–4 unadjusted COVID-19 vaccine doses.

As for its findings, the agency said that after 2–3 months of vaccination in those aged 18 – 49 years, bivalent boosters maintained 52% effectiveness against BA.5 infection and 48% against XBB/XBB.1.5 infection, compared to unadjusted vaccines.

The agency used more than 29K COVID tests between December 01, 2022 – January 21, 2023, to conduct the study.

“Bivalent vaccines appear to provide additional protection against symptomatic BA.5-related sublineage and XBB/XBB.1.5-related sublineage infections in persons who had previously received 2, 3, or 4 monovalent vaccine doses,” the CDC wrote.

The findings support “recommendations to continue to increase bivalent booster coverage,” the agency added.

However, the self-reported nature of vaccination status, infection history, and previous medical conditions, as well as lack of control for time since the last monovalent shot, were among the study limitations.

The report comes a day before an FDA advisory committee meeting on how to update currently available COVID-19 vaccines and boosters to face a fast-changing virus.