Late-Breaker: COVID-19 mRNA-1273 Booster Most Effective Among Adults Aged 65 and Older During Delta, Omicron Surges

A booster dose of the mRNA-1273 vaccine provided significant additional protection against COVID-19 infection during the pandemic’s Delta and Omicron waves, according to data released at IDWeek 2023 today, with the observed effects much greater among adults aged 65 years and older.

The findings, based on analysis of data from the COVE (Coronavirus Efficacy) trial, were presented by Dean Follmann, PhD, assistant director for biostatistics at the National Institute of Allergy and Infectious Diseases of the NIH, during a late-breaking oral abstract session. IDWeek is taking place in Boston, MA, from October 11-15.

Results of the analysis, which examined the effects of age and interval between vaccine doses on the risk of COVID-19 during surges of the highly infectious Delta and Omicron variants, contribute to more robust understanding of both factors, understanding, the authors write, that is “critical for public health policy.”

Data for analysis of the booster shot were derived from a cohort of approximately 17 000 participants in the phase 3 COVE trial who received a third dose of mRNA-1273 50 μg (booster) having previously received a 2-dose series of 100 µg mRNA-1273 during the randomized placebo-controlled phase (mRNA-1273, 1st dose July to October 2020), or open label phase (placebo-mRNA-1273, 1st dose December 2020 to April 2021).

COVE participants received a single booster dose of 50 µg mRNA-1273 beginning in September 2021. Using Cox regression models, investigators assessed the effect of the booster administration on risk of COVID-19 stratified by the initially randomized study arm, the time since the booster shot, and age (younger than age 65 years and age 65 years and older). The assessment period was between September 2021 and May 2022, during the open label phase of the COVE study.

RESULTS

The research team reported median dosing intervals (IQR) between the primary vaccination series and the booster shot were 8.2 (7.8-8.7) months for the placebo-mRNA-1273 and 12.9 (12.3-13.5) months for the mRNA-1273 arms.

According to the study, the booster dose was associated with “substantial additional protection” against infection with COVID-19 through 60 days during the Delta surge and protection also was high against the Omicron BA.1 variant but waned over time through 110 days.

The finding that the risk of infection after a booster dose during the Omicron phase was lower by 24% (95% CI, 16% to 32%) in the mRNA-1273 vs the placebo-mRNA arm suggests to the researchers that there may be a benefit to a longer interval between receiving a primary vaccine series and a booster shot.

When they analyzed the data by age, investigators reported the initial booster efficacy against the Omicron variant in adults aged 65 years and older was 86% (95% CI, 69% to 93%) but after approximately 4 months that protection had waned to 28% (95% CI, -47% to 65%).

The analogous estimates for COVE participants younger than age 65 years were an initial increase in efficacy of 50% (95% CI, 36% to 61%) with a fall off at 4 months to 6% (95% CI, 129% to 31%).

When data were stratified by study arm, the initial boost in efficacy against the Omicron variant in those older than 65 years was 79% (95% CI, 41% to 92%) for the placebo-mRNA arm and 91% (95% CI, 79% to 96%) for mRNA-1273, according to the study. For the younger than age 65 years group, the corresponding estimates were 52% (95% CI, 30% to 62%) and 55% (95% CI, 39% to 66%), respectively. These results investigators observed suggest that the effect of the length of the booster interval was “largely concentrated” in the cohort group aged 65 years and older.

The research team concludes that boosting immunity with a third does of mRNA-1273 was effective during the Delta and Omicron variant surges of the COVID-19 pandemic but that the reduced risk of infection became diluted over time (~4 months in the study). The greatest benefits of receiving the booster dose and of the dosing interval were observed in the study population older than age 65 years, information that will help public health officials in planning for future immunization efforts.

Source: Follman D, Wang X, Gilbert P, et al. Who to boost and when: an analysis of dosing interval and age on COVID-19 outcomes in the COVE trial during the Delta and Omicron waves. Abstract presented at IDWeek 2023; October 13, 2023; Boston, MA.

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