The latest 2023-2024 COVID-19 vaccine has shown an overall effectiveness of 54% against symptomatic cases in adults, according to a study by CDC researchers. The vaccine also demonstrated efficacy against the JN.1 variant, which became predominant in January.
The study, published in the Morbidity and Mortality Weekly Report, revealed that vaccine effectiveness varied by age group, with a 57% effectiveness for individuals aged 18 to 49 and a slightly lower 46% for those aged 50 and older. The updated vaccine is a monovalent XBB.1.5-derived vaccine, and this research is the first to assess its effectiveness against symptomatic COVID caused by the JN.1 variant, a derivative of BA.2.86.
The data, obtained from the CDC’s Increasing Community Access to Testing program, included no-cost SARS-CoV-2 nucleic acid amplification tests provided at CVS and Walgreens pharmacies from September 2023 to January 2024. The vaccine’s effectiveness was found to be 58% among those tested 7 to 59 days after vaccination and 49% among those tested 60 to 119 days after receipt.
The researchers conducted a subanalysis, differentiating XBB lineages from JN.1 and other Omicron BA.2.86 lineages using reverse transcription-polymerase chain reaction (RT-PCR) COVID tests. The study found that vaccine effectiveness against JN.1 lineages was 49%, while it was 60% for non-JN.1 lineages among individuals who had received the updated vaccine 60 to 119 days earlier.
The authors emphasized the relatively brief period covered in the study, which only looked at data through 119 days since vaccination. They noted that waning effectiveness is expected over time, especially against less severe disease.
In September 2023, the CDC’s Advisory Committee on Immunization Practices recommended the updated COVID vaccine for everyone aged 6 months and older. However, the study highlighted that only 12% of people tested reported receiving the updated vaccine, while over 26% had never received any COVID vaccine. Vaccination status and previous infection history were self-reported, introducing potential bias into the results.
Despite the limitations, the study provides valuable insights into the effectiveness of the latest COVID-19 vaccine, emphasizing the need for ongoing research as new variants emerge and vaccination efforts continue.