XBB.1.5 updated COVID vaccine booster offers 54% increased protection against symptomatic infection

By Tarun Sai LomteFeb 4 2024Reviewed by Susha Cheriyedath, M.Sc.

In a recent study published in Morbidity and Mortality Weekly Report, researchers estimated the effectiveness of the 2023-24 updated coronavirus disease 2019 (COVID-19) vaccine.

The Advisory Committee on the Immunization Practices of the United States (US) Centers for Disease Control and Prevention (CDC) recommended on September 12, 2023, that all individuals aged six months or older receive the 2023-24 updated monovalent COVID-19 vaccine. The updated vaccine contains a component from the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron XBB.1.5 lineage and lacks ancestral strain components.

The JN.1 lineage was identified in the US in September 2023, which harbors 30 additional mutations in the spike (S) protein compared to XBB.1.5. Real-time reverse-transcription polymerase chain reaction (RT-PCR) results can help distinguish some SARS-CoV-2 lineages. S-gene target failure (SGTF) is detected in JN.1 and other BA.2.86 lineages, whereas S-gene target presence (SGTP) is detected in most lineages from 2023, including XBB.

Study: 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. Image Credit: New Africa / Shutterstock

About the study

In the present study, researchers estimated the effectiveness of the 2023-24 updated COVID-19 vaccine against symptomatic infection. They included tests conducted between September 21, 2023, and January 14, 2024, among adults reporting at least one symptom. Cases were individuals with a positive nucleic acid amplification test (NAAT).

Controls were individuals with a negative NAAT. The team excluded tests from Janssen vaccine recipients, Novavax recipients, immunocompromised individuals, those who received the most recent vaccine dose within a week preceding testing, and those with a positive COVID-19 test within the past 90 days.

Vaccine effectiveness (VE) against symptomatic COVID-19 was estimated by comparing the odds of receipt of the updated vaccine versus non-receipt among cases and controls. Multivariable logistic regression was used to estimate odds ratios. VE was computed separately by SGTP and SGTF status. Test-positive samples with reduced or null S-gene amplification were deemed to have an SGTF, whereas those without SGTF were considered SGTP.

Findings

Of over 9,200 NAAT results for individuals with symptoms of COVID-19-like illness, 3,295 tested SARS-CoV-2-positive. Around 1,125 individuals received the updated COVID-19 vaccine ≥ seven days earlier. More controls received the updated vaccine than cases. The median time from the last dose among updated vaccine recipients was 60 days for cases and 51 days for controls.

Nearly 8,100 individuals did not receive the updated vaccine. Of these, 30% were non-vaccinated and 70% were vaccinated. Among the vaccinated, the median time since vaccination was 378 days for cases and 363 days for controls. The estimated VE was 57% in the 18–49 age group and 46% among those aged ≥ 50. VE was estimated at 58% and 49% among people tested 7–59 and 60–119 days after receiving the updated vaccine, respectively.

There were 679 tests available with S-gene target results. Of these, 258 showed SGTF, and 421 exhibited SGTP. VE was not precise for tests with SGTF during the 7–59 days post-receipt of the updated vaccine, given the emergence of JN.1 in the US. VE during the 60–119 days post-receipt of the updated vaccine was 60% for tests with SGTP and 49% for those with SGTF.

Conclusions

The study provided early efficacy estimates of the updated monovalent XBB.1.5 vaccine against symptomatic infection and the first VE estimates against the JN.1 lineage. These VE estimates include data up to 119 days post-vaccination. However, VE will likely wane with time since vaccination, as observed after the original monovalent or bivalent COVID-19 vaccination. Prior infection history, medical conditions, and vaccination status were self-reported, thereby subject to recall bias.

Besides, the VE estimates were computed for a population that opted to be tested for COVID-19; therefore, the estimates are subject to selection biases. Further, coverage of the updated vaccine is low among adults and varies by age. Taken together, the updated monovalent vaccine provided 54% protection from symptomatic illness. Waning of the VE is expected over time, especially against less severe outcomes.