Most COVID-19 vaccines effective as boosters, regardless of primary series
Six COVID-19 vaccines increased protection when given as booster shots 10 to 12 weeks after a two-dose primary series of the Pfizer-BioNTech vaccine, according to results from a randomized controlled trial published in The Lancet.
The trial also demonstrated that the same six vaccines — plus one more — increased protection when given as boosters after a two-dose primary series of the Oxford-AstraZeneca vaccine, which is not available in the United States but is being used in more than 180 countries.
Saul N. Faust, PhD, director of the Southampton NIHR Wellcome Trust Clinical Research Facility in the United Kingdom, and colleagues conducted a multicenter, randomized, controlled phase 2 trial of third dose COVID-19 boosters among 2,878 participants aged 30 years or older between June 1 and June 30.
Each participant received either the Pfizer-BioNTech COVID-19 messenger RNA vaccine or the Oxford-AstraZeneca adenovirus vaccine as their two-dose primary series. In addition to those vaccines, the other five shots used for booster doses in the study were the vaccines made by Johnson & Johnson, Moderna, Valneva, CureVac and Novavax.
A total of 13 experimental and control arms were created for the study — seven vaccines, plus three at half doses, and three control arms. Participants were split into three groups, each composed of six sites per group. Primary outcomes were assessed 28 days after receiving a booster dose.
Among participants who received the Oxford vaccine as a primary series, all seven vaccines raised anti-spike protein antibody levels after 28 days as booster shots, ranging from 1.8 times higher (99% CI, 1.5-2.3) in the half-Valneva group to 32.3 times higher (99% CI, 24.8-42) in the Moderna group.
Participants who received the Pfizer vaccine experienced increases that ranged from 1.3 times higher (99% CI, 1-1.5) in the half-Valneva group to 11.5 times higher (99% CI, 9.4-14.1) in the Moderna group.
The upper limit of the 99% confidence interval for full and half doses of the Valneva vaccine did not reach the pre-established minimum clinically important difference of 1.75.
“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,” Faust said in a news release.
“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. “Further work will generate data at 3 months and 1 year after people have received their boosters, which will provide insights into their impact on long-term protection and immunological memory.”
Perspective
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This is a tour-de-force study, and it supports the mix-and-match approach. It also suggests that, regardless of what COVID-19 vaccine you received first — with the possible exception of CureVac — an mRNA booster is best.
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