The science behind mixing and matching COVID-19 vaccines

Last week, each the Federal Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) beneficial booster vaccinations against Covid-19 for specific populations and in addition endorsed a “mix and match” approach. This would allow health care providers to provide patients a special booster shot than the one they originally received. Why was this decision made and what’s the scientific basis behind it?

Heterologous Prime-Boost strategy

Many vaccines are given in multi-dose series with the identical vaccine, which known as the homology approach. The first dose will stimulate the immune system’s B cells to supply antibodies against the pathogen and stimulate T cells to acknowledge and destroy infected cells. The second dose often increases and intensifies this immune response. The polio vaccine requires a series of 4 doses, while the diphtheria-tetanus-pertussis combination vaccine requires a series of 5 doses and a booster to supply full immunity. International studies on COVID-19 have used a heterologous primary and booster vaccination strategy, by which one vaccine is used as the first dose and another vaccine is used because the second dose. Research by Nordström, Ballin, and Nordström (2021) found that any such vaccination regimen is an “effective alternative in increasing population immunity against Covid-19.” Their study, which used a viral vector vaccine (approved by Oxford/AstraZeneca for emergency use in Europe) as a primary dose and an mRNA vaccine (from Pfizer/BioNTech or Moderna) as a second dose, showed an efficacy of 67 –79%. against symptomatic COVID-19 infection in comparison with 50% effectiveness using the viral vector vaccine alone.

Mixing vaccines has the potential to supply a broader and stronger response than a single vaccine, and various kinds of vaccines stimulate the immune system in alternative ways (Zimmer, 2021). In the US, although research is restricted, early data suggests that booster doses of the Moderna or Pfizer-BioNTech mRNA vaccines were simpler at increasing antibody levels in comparison with the Janssen/Johnson & Johnson (J&J) vaccine (Mandavilli, 2021). . Data from a study by Atmar et al. (2021) found that the Janssen/J&J vaccine increased antibody levels only four-fold, while the Pfizer-BioNTech booster improved antibody levels 35-fold and the Moderna booster increased 76-fold. However, this study is preliminary and has not yet been peer-reviewed.

The advice for a booster dose applies to older people and people at high risk. Advocating for a mix-and-match strategy provides greater flexibility by way of ease of access and availability at local pharmacies and provider offices. However, the FDA and CDC don’t recommend using one vaccine booster over one other and can as an alternative allow health care providers and individuals to make decisions based on available data.

Information regarding Covid-19 infection, its variants and vaccines is continuously evolving. We’ll do our greatest to maintain you updated with the most recent recommendations as they develop into available.

Atmar, R. L., Lyke, K. E., Deming, M. E., Jackson, L. A., Branche, A. R., El Sahly, A. M., et al. (2021). Heterologous SARS-CoV-2 booster vaccinations – preliminary report. . https://doi.org/10.1101/2021.10.10.21264827

Mandavilli, A. (2021, October 21). The CDC recommends Covid booster shots for tens of millions of Americans. . Retrieved October 22, 2021 from https://www.nytimes.com/2021/10/21/health/covid-vaccine-boosters-cdc.html?campaign_id=9909069 and segment_idi. 198AA4BD46687E8247E8484C42B3

Nordstrom, P., Ballin, M., and Nordstrom, A. (2021). Efficacy of a heterologous ChAdOx1 nCoV-19 and mRNA primary vaccine against symptomatic Covid-19 infection in Sweden: a nationwide cohort study. . https://doi.org/10.1016/j.lanepe.2021.100249

Zimmer, C. (2021, October 19). Mix and match Covid: Whey boosters just might work. . Retrieved October 22, 2021 from https://www.nytimes.com/2021/10/19/health/covid-vaccine-mix-match.html