Exploring the vaccine efficacy of COVID-19 booster vaccine doses
Exploring the vaccine efficacy of COVID-19 booster vaccine doses

Exploring the vaccine efficacy of COVID-19 booster vaccine doses

In a recent study posted to medRxiv* preprint server, researchers compared the effectiveness of the booster vaccine for coronavirus disease 2019 (COVID-19) with that of the primary vaccine series.

Examination: The efficacy of COVID-19 mRNA vaccine booster dose over primary series during a period of Omicron circulation. Image credit: Dmitry Demidovich / Shutterstock


To date, over five million confirmed cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) cases, including 6.2 million deaths, have been reported globally. COVID-19 vaccines have played a crucial role in slowing down Transfer of covid-19; however, the decreasing efficiency of these vaccines have led to the administration of booster vaccines for better protection against infection and the severity of the disease.

About the study

The researchers in this study estimated the relative vaccine efficacy (RE) of COVID-19 messenger ribonucleic acid (mRNA) booster vaccines compared to the primary two-dose vaccine series.

The study included vaccinated participants from an ongoing longitudinal study called the prospective assessment of COVID-19 in a community (PACC) between December 20, 2021 and February 24, 2022. Participants who were 12 years of age and older and eligible to receive a booster dose, i.e., five months had elapsed since the participant had completed their primary mRNA vaccine series. Nearly 96% of the samples sequenced during the follow-up period were infected with the SARS-CoV-2 Omicron variant.

The team estimated the risk ratio for SARS-CoV-2 infections in individuals vaccinated with the primary series compared to those who had received their booster vaccine dose. Persons belonging to the primary vaccine series were vaccinated either after 20 December 2021 or five months or more after receiving the second dose, whichever came later, and before the administration of the third dose or the end of the study, all after what was first. Individuals belonging to the booster vaccinated cohort had received their vaccine after December 20, 2021, or 14 days or more after the administration of the third dose, whichever came later.

The team performed sensitivity analyzes to evaluate VE for all participants except those who reported an immunocompromised condition or those who had previously been infected with SARS-CoV-2 before December 20, 2021. A history of SARS-CoV-2 infection was also reported. defined as a positive SARS-CoV-2 test result before December 20, 2021 or self-reported during study enrollment.


The results of the study showed that 884 people participated in the study. These participants ranged in age from 12 to 90 years, while 62% of them were women and 42% had one or more chronic health conditions. Nearly 26% of participants had completed their primary vaccine dose, while 74% of participants had received a booster vaccine dose by the end of the follow-up period. In particular, the median time between the end of the primary series and the beginning of the follow-up period was 233 and 275 days for non-boosted and boosted participants, respectively. In addition, the median time from receipt of the booster vaccine to the beginning of the follow-up period was 33 days for participants who had received their booster dose.

Among individuals who had completed the primary series but had not received the booster dose, 74% had received two doses of the BNT162b2 vaccine, 26% had received two doses of the mRNA-1273 vaccine, and none were administered with mixed products. Among boosted participants, a total of 62% were vaccinated with two doses of BNT162b2, 38% with two doses of mRNA-1273, and 0.2% with mixed products during their primary vaccine series. Approx. 65% and 35% of the booster doses were BNT162b2 and mRNA-1273, respectively.

Out of 9.3% of the identified SARS-CoV-2 infections, 46 were reported after the primary dose and 36 after receiving the booster dose. This correlated with the incidence of SARS-CoV-2 of 9.6 / 10,000 personal days among booster dose vaccinated and 34.6 / 10,000 personal days among primary serial vaccinated. The study also estimated the relative RE to 66% for boosted individuals compared to those vaccinated with the primary series only.

SARS-CoV-2 infections before December 20, 2021 were reported by 23% of the primary serial vaccinated and 18% of the boosted individuals. Furthermore, re-infection was observed in only one vaccinated primary series among the 172 participants who reported a previous infection.

Overall, the study results showed that the efficacy of the vaccine against SARS-CoV-2 was short-lived and was affected by a decreasing immune response to infection. The researchers believe that routine SARS-CoV-2 vaccinations are necessary to combat the COVID-19 pandemic.

*Important message

medRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered as crucial, guide clinical practice / health-related behavior or be treated as established information.

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