Multiple COVID-19 Boosters Safe, Immunogenic Following 2 Doses of AstraZeneca, Pfizer-BioNTech Vaccines


The study examined safety, immune response (immunogenicity), and adverse effects of 7 vaccines when used as a third booster jab.

The first randomized trial of COVID-19 boosters given after 2 doses of either the ChAdOx1-nCov19 (Oxford–AstraZeneca, ChAd) or BNT162b2 (Pfizer-BioNTech, BNT) vaccines, published in The Lancet, found that 6 different boosters are safe and provoke strong immune responses in participants aged 30-69 years and those aged 70 years or older.

“It’s really encouraging that a wide range of vaccines, using different technologies, show benefits as a third dose to either AstraZeneca or Pfizer-BioNTech,” said Saul Faust, MA, MBBS, FRCPCH, PhD, FHEA, director of the NIHR Clinical Research Facility, University Hospital Southampton NHS Foundation Trust, in a press release. “That gives confidence and flexibility in developing booster programs here in the UK and globally, with other factors like supply chain and logistics also in play.”

The study examined safety, immune response (immunogenicity), and adverse effects of 7 vaccines when used as a third booster jab. These vaccines included ChAd, BNT, NVX-CoV2373 (Novavax, NVX), Ad26.COV2.S (Janssen, Ad26), Moderna (mRNA1273), VLA2001 (Valneva, VLA), and CVnCov (Curevac, CVn).

“The side effect data show all 7 vaccines are safe to use as third doses, with acceptable levels of inflammatory side effects like injection site pain, muscle soreness, fatigue,” Faust said in the release. “Whilst all boosted spike protein immunogenicity after two doses of AstraZeneca, only AstraZeneca, Pfizer-BioNTech, Moderna, Novavax, Janssen and Curevac did so after two doses of Pfizer-BioNTech.”

Increases in anti-spike protein antibody levels after 28 days varied across the vaccines. Patients who had received 2 doses of ChAd as their initial vaccination series had increases ranging from 1.8 times higher to 32.3 times higher, dependent on which booster vaccine was used. In patients who received BNT, the range was 1.3 times higher to 11.5 times higher.

According to the investigators, at the 28-day review, all booster results were similar for participants aged 30-69 years and those aged 70 years or older. The researchers caution that these boost ratios relate to immunogenicity as opposed to protection against disease, with the relationship between antibody levels at day 28 and long-term protection and immunological memory remaining unknown.

“It’s important to note that these results relate only to these vaccines as boosters to the two primary vaccinations, and to the immune response they drive at 28 days,” Faust said in the release. “Further work will generate data at three months and one year after people have received their boosters, which will provide insights into their impact on long-term protection and immunological memory. We are also studying two of the vaccines in people who had a later third dose after 7-8 months although results will not be available until the new year.”


THE LANCET: Six different COVID-19 boosters are safe and increase immunity when given after two doses of AstraZeneca or Pfizer-BioNTech, with large variations in immune responses, UK trial shows [news release]. EurekAlert; December 2, 2021. Accessed December 8, 2021.

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