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Updated Monovalent COVID-19 Vaccines Effective Against Symptomatic Infection, Emerging Variants


The updated COVID-19 vaccines were approximately 54% effective against symptomatic SARS-CoV-2 infection, according to new data from the CDC.

Updated Monovalent COVID-19 Vaccines Effective Against Symptomatic Infection, Emerging Variants / Image credit: ©Talia Mdlungu/peopleimages.com/AdobeStock

©Talia Mdlungu/peopleimages.com/AdobeStock

Receipt of an updated monovalent COVID-19 vaccine provided approximately 54% increased protection against symptomatic SARS-CoV-2 infection compared to no receipt, according to early estimates published by the US Centers for Disease Control and Prevention (CDC).

The data published February 1, 2024, in the CDC’s Morbidity and Mortality Weekly Report also showed that monovalent COVID-19 vaccines provided protection against JN.1 and XBB lineages.

“In September 2023, CDC’s Advisory Committee on Immunization Practices recommended updated 2023–2024 (monovalent XBB.1.5) COVID-19 vaccination for all persons aged ≥6 months to prevent COVID-19, including severe disease,” wrote first author Ruth Link-Gelles, PhD, of the CDC’s National Center for Immunization and Respiratory Diseases, and colleagues. “Many variants co-circulated during fall 2023; the JN.1 lineage became predominant in January 2024. Few estimates of updated 2023–2024 vaccine effectiveness (VE) are available.”

To assess VE of the updated monovalent COVID-19 vaccines, investigators analyzed data on 9222 adults who reported ≥1 symptom for COVID-19 and who were tested for SARS-CoV-2 infection as part of the CDC’s Increasing Community Access to Testing at a CVS or Walgreens pharmacy between September 21, 2023, and January 14, 2024.

“Whereas the goal of the U.S. COVID-19 vaccination program is to prevent severe disease, VE against symptomatic infection can provide useful insights into protection early after introduction of updated vaccines and during the emergence of new lineages, such as JN.1,” wrote Link-Gelles and colleagues.

According to the study, case-patients were persons who received a positive nucleic acid amplification test (NAAT) result for COVID-19 and control patients were those who received a negative NAAT result.


Among the 9222 adults with ≥1 symptom for COVID-19, 3295 (36%) were positive for SARS-CoV-2, according to the results. Among 1125 persons who had received updated monovalent COVID-19 vaccine ≥7 days earlier, more control patients (n=844; 14%) reported having received the vaccine than did case-patients (n=281; 9%).

Among 8097 persons who reported that they had not received an updated vaccine dose, 2435 (30%) were unvaccinated. Among the remaining 5662 participants (70%) who had received only original COVID-19 vaccines and not an updated vaccine dose, the median interval since their last dose was 378 days for case-patients and 363 days for control patients.

Overall, VE was 54% (95% CI, 46%-60%) among individuals who had recently received an updated COVID-19 vaccine at a median of 52 days after vaccination. Also, investigators found that VE for persons aged 18-49 years was 57% (95% CI, 48%-65%) and for those aged ≥50 years was 46% (95% CI, 31%-58%).

In addition, VE was 58% (95% CI, 48%–65%) among participants who received testing 7–59 days after receipt of updated COVID-19 vaccine and 49% (95% CI, 36%–58%) among those who received testing 60–119 days after receipt of the vaccine.

In a subanalysis of 2199 tests performed at a laboratory with S-gene target failure (SGTF) testing, researchers noted that VE 60–119 days after vaccination was 49% (95% CI, 19%-68%) among tests exhibiting SGTF and 60% (95% CI, 35%-75%) among those without SGTF.

“Waning of effectiveness is expected with additional elapsed time since vaccination, especially against less severe disease. CDC will continue to monitor trends in VE,” concluded Link-Gelles et al. “All persons aged ≥6 months should stay up to date with COVID-19 vaccination, including receiving a dose of updated vaccine.”

Source: Link-Gelles R, Ciesla AA, Mak J, et al. Early estimates of updated 2023–2024 (monovalent XBB.1.5) COVID-19 vaccine effectiveness against symptomatic SARS-CoV-2 infection attributable to co-circulating omicron variants among immunocompetent adults — Increasing Community Access to Testing Program, United States, September 2023–January 2024. MMWR Morb Mortal Wkly Rep. 2024;73:77–83. doi: http://dx.doi.org/10.15585/mmwr.mm7304a2

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