Study explores efficacy of mRNA vaccine booster doses during the SARS-CoV-2 Omicron wave

In a recent study posted to The Lancet* preprint server, researchers evaluated the efficacy of a messenger ribonucleic acid (mRNA) vaccine booster dose against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) during the Omicron surge.

Study: The Effectiveness of mRNA Vaccine Boosters for Laboratory-Confirmed COVID-19 During a Period of Predominance of the Omicron Variant of SARS-CoV-2. Image Credit: chatuphot/Shutterstock

Coronavirus disease 2019 (COVID-19) infections have recently increased to record-high numbers across many regions, including countries where vaccination coverage is considerably high. The SARS-CoV-2 Omicron variant is responsible for the latest wave of COVID-19 infections, since it carries over 35 mutations, many in its spike (S) protein, that impart enhanced pathogenic characteristics to the variant.

The emergence of mutants throughout the pandemic is alarming because the amino acid substitutions they harbor might impair the available therapeutic and prophylactic measures. Several vaccine breakthrough infections and reinfections due to the SARS-CoV-2 Omicron variant have been documented. Moreover, studies observed reduced effectiveness of therapeutic antibodies used for COVID-19 treatment against the Omicron variant.

Although the currently used COVID-19 vaccines provide significant immunity against severe disease, their efficacy against SARS-CoV-2 variants is diminished given that vaccines are based on the ancestral or wildtype isolate of SARS-CoV-2. Vaccine-elicited antibody responses wane after a certain period, and therefore, several countries have approved booster doses to enhance immunity.

The study

In the present study, researchers assessed the efficacy of booster shots of mRNA (BNT162b2 and mRNA-1273) vaccines in Spain for people aged ≥ 40 years during the latest surge of infections driven by the Omicron variant. The core objective was to investigate COVID-19 diagnosis between January 1, 2022, and February 6, 2022. mRNA vaccinees were eligible for a booster dose six months after primary vaccination and subsequently recipients of Ad26.COV2.S and ChAdOx1 vaccines were approved for mRNA boosters (heterologous immunization).

Data on vaccinations and diagnostic test results available on REGVACU and SERLAB registries, respectively, were linked with the national health system registry using the national identification number. SERLAB hosts all COVID-19-related polymerase chain reaction (PCR) and rapid antigen test results, and from December 21, 2021, self-reported antigen test results were also included in the database.

Upon meeting the matching criteria, boosted subjects were matched randomly with individuals from the control cohort (no-booster). A head-to-head comparison was made between the recipients of BNT162b2 and mRNA-1273 booster vaccines.

Findings

More than half of 7 million eligible subjects received an mRNA booster, with over 52 % of them taking a COVID-19 test since the pandemic. Among the boosted individuals, around 47,104 SARS-CoV-2 infections were recorded during the study compared to >93,000 in the no-booster group. COVID-19 infection risk stood at 2.7% for booster recipients and 5.4 % for control subjects. The test positivity rate was 25.4% for the booster group and 37% for the control group.

Overall, the efficiency of booster shots was 51.3% in seven to 34 days of the follow-up period, reflecting protection of 186 subjects per 10,000 individuals. Females and people aged between 60 and 69 years demonstrated higher booster effectiveness than males and those aged between 40-49 years.

For people who received ChAdOx1 or mRNA-1273 vaccines in primary vaccination, booster efficiency was 55-59% and in Ad26.COV2.S or BNT162b2 vaccinees was 48-50%. A longer interval between primary and booster vaccination was associated with improved efficacy. Boosting with the mRNA-1273 vaccine (52.5 %) had higher efficiency than with the BNT162b2 vaccine (46.2 %). Further analysis estimated 13% higher protection for mRNA-1273 booster recipients over BNT162b2-boosted subjects.

Conclusions

The study findings show that the calculated effectiveness of mRNA booster vaccines was 51% against COVID-19 diagnosis. Moderna's mRNA-1273 vaccine was 13% more effective than Pfizer's BNT162b2 vaccine. The authors reported that the efficacy of mRNA vaccines was lower than that observed during the period of Delta variant predominance. The administration of booster shots after six months since primary vaccination resulted in 52% efficiency in contrast to 44% if the boosters were provided within six months of the complete vaccination course.

Notably, the present research could not address the booster efficacy against the severe clinical course of COVID-19 and COVID-19-related deaths as the registries used for the study lack regular updates of such information. Taken together, the findings demonstrate that mRNA booster vaccines could moderately protect the recipients from Omicron infection for up to 30 days. More research is needed to estimate the full duration of immunity conferred by booster shots against the Omicron variant.

*Important notice

Preprints with The Lancet publish preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Tarun Sai Lomte

Tarun is a writer based in Hyderabad, India. He has a Master’s degree in Biotechnology from the University of Hyderabad and is enthusiastic about scientific research. He enjoys reading research papers and literature reviews and is passionate about writing.