Study highlights benefit of mRNA boosters for SARS-CoV-2 following different initial vaccine types

By Dr. Tomislav Meštrović, MD, Ph.D.Feb 8 2022Reviewed by Emily Henderson, B.Sc.

A study by researchers from the United Kingdom finds no difference in the protection offered by mRNA vaccine boosters against the severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) when comparing those that have received BioNTech/Pfizer vaccine as a primary course to those that have received Oxford/AstraZeneca. The paper is currently available on the medRxiv* preprint server while undergoing peer review.

Study: Comparative effectiveness of different primary vaccination courses on mRNA based booster vaccines against SARs-COV-2 infections: A time-varying cohort analysis using trial emulation in the Virus Watch community cohort. Image Credit: Corona Borealis Studio/ Shutterstock

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources

During the unprecedented spread of the Omicron (B.1.1.529) variant of SARS-CoV-2, the infections in double vaccinated individuals have increased around the world, particularly in those that have received the ChAdOx1 (Oxford/AstraZeneca) vaccine.

Consequently, in order to tackle such a surge in SARS-CoV-2 infections and coronavirus disease 2019 (COVID-19) cases, the United Kingdom has accelerated booster vaccination programs that have used mRNA vaccines as boosters – irrespective of an individual’s primary course vaccine type.

However, the understanding is still limited to the exact effectiveness of mRNA-based booster vaccine doses following various primary vaccination courses, especially when considering time-varying confounders that may impact different comparative approaches.

This paper, led by Dr. Vincent Grigori Nguyen from the University College London (on behalf of the Virus Watch Collaborative), used a particular methodological approach to adequately estimate the comparative effectiveness of receiving different primary vaccine courses in addition to an mRNA booster vaccine against SARS-CoV-2 in a general population community cohort.

A prospective study on Virus Watch community cohort

In a nutshell, this prospective observational study utilized the Virus Watch community cohort in England and Wales, which comprises 19,692 individuals across England and Wales who received their booster vaccination against SARS-CoV-2 between September 16, 2021, and January 5, 2022.

The authors aimed to apply specific trial emulation techniques in order to account for time-varying confounding by indication. Moreover, specific eligibility criteria have been used to remove those likely protected from SARS-CoV-2 (for example, through prior natural infection) and stagger the cohort based upon vaccination date.

The latter step allowed similar individuals to have similar follow-up periods, but even more importantly, to experience identical COVID-19 public health policies and viral reproduction rates – not only at the time of vaccination but also during the follow-up period.

No difference in SARS-CoV-2 infection incidence

The study has found that individuals who received Oxford/AstraZeneca vaccinations as their primary course did not differ in the incidence of SARS-CoV-2 infection in comparison to those that have received BioNTech/Pfizer (BNT162b2) during the follow-up period and after accounting for differences in vaccine timing, as well as demographic and clinical characteristics.

In other words, there is strong evidence here of the same effectiveness of BioNTech/Pfizer compared to Oxford/AstraZeneca vaccines against SARS-CoV-2 infection after receiving a booster vaccination in England and Wales.

This finding actually diverges from previous analysis that showed how boosters after Oxford/AstraZeneca primary vaccine course are linked to a higher risk of infection.

A notable strength of this analysis is that the authors have been able to estimate vaccine effectiveness in a cohort of people with large numbers of those belonging to clinically vulnerable or extremely vulnerable groups, which were actually prioritized for booster doses based upon need.

Maintaining protection

These findings underscore the importance of mRNA booster doses in maintaining protection against COVID-19, particularly for those that received a primary course of Oxford/AstraZeneca, which may be related to different antibody levels.

“We have also shown that following an mRNA booster dose antibody levels are similar regardless of the primary course and hypothesize that this accounts for the similar effectiveness of mRNA boosters regardless of primary regime,” say study authors in this medRxiv paper.

In addition, their approach also adequately accounts for “time zero” (i.e., the start of follow-up), since it avoids comparisons between individuals who were experiencing different public health policies and SARS-CoV-2 reproduction rates through time.

In conclusion, these findings are especially pertinent, considering the ongoing spread of the SARS-CoV-2 Omicron variant, and the paper opens the door for using this type of approach in the future to appraise the real-world effectiveness of different vaccine combinations.

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources