AstraZeneca reports that its COVID-19 vaccine (Vaxzevria), when given as a third dose booster, increased the immune response to Beta, Delta, Alpha and Gamma SARS-CoV-2 variants, while a separate analysis of samples from the trial showed increased antibody response to the Omicron variant.

The results of the company’s preliminary analysis of an ongoing safety and immunogenicity trial were observed among individuals previously vaccinated with either Vaxzevria or an mRNA vaccine.

A separate Phase IV trial reported in a preprint with The Lancet on SSRN showed that a third dose of Vaxzevria substantially increased antibody levels following a primary vaccine series with CoronaVac (Sinovac Biotech).1

These data add to the growing body of evidence supporting Vaxzevria as a third dose booster irrespective of the primary vaccination schedules tested.2,3 The Company is submitting these additional data to health authorities around the world given the urgent need for third dose boosters.

Sir Mene Pangalos, Executive Vice President, BioPharmaceuticals R&D, AstraZeneca, said: “Vaxzevria has protected hundreds of millions of people from COVID-19 around the world and these data show that it has an important role to play as a third dose booster, including when used after other vaccines. Given the ongoing urgency of the pandemic and Vaxzevria’s increased immune response to the Omicron variant, we will continue to progress regulatory submissions around the world for its use as a third dose booster.”

Professor Sir Andrew J Pollard, chief investigator and director of the Oxford Vaccine Group at the University of Oxford, said: “These important studies show that a third dose of Vaxzevria after two initial doses of the same vaccine, or after mRNA or inactivated vaccines, strongly boosts immunity against COVID-19. The Oxford-AstraZeneca vaccine is suitable as an option to enhance immunity in the population for countries considering booster programmes, adding to the protection already demonstrated with the first two doses.”

The D7220C00001 safety and immunogenicity trial showed that Vaxzevria continued to be generally well tolerated. Further analyses from the trial are expected in the first half of 2022.

Previous studies support Vaxzevria as a third dose booster as part of a homologous or heterologous schedule.2,3 In a sub-analysis from the COV001 and COV002 trials, a third dose of Vaxzevria given at least six months after a second dose significantly boosted antibody levels and maintained T cell response.2 It also resulted in higher neutralising activity against the Alpha, Beta, and Delta variants, compared with a two-dose regimen.The COV-BOOST trial also showed that a third dose booster of Vaxzevria induced significantly higher immune responses compared with controls against the Delta variant and original strain following a primary vaccine series of Vaxzevria or Pfizer BioNtech (BNT162b2).3

1.     Costa Clemens SA, et al. Randomized immunogenicity and safety study of heterologous versus homologous COVID-19 booster vaccination in previous recipients of two doses of CoronaVac COVID-19 Vaccine. Preprint 2021. Available at SSRN: [Last accessed: January 2022]. Preprints with TheLancet available via the SSRN platform are not Lancet publications and have not been peer-reviewed.
2.     Flaxman A, et al. Reactogenicity and immunogenicity after a late second dose or a third dose of ChAdOx1 nCoV-19 (AZD1222) in the UK: a substudy of two randomized controlled trials (COV001 and COV002). The Lancet. 2021;398:981-990.
3.     Munro A PS, et al. Safety and immunogenicity of seven COVID-19 vaccines as a third dose (booster) following two doses of ChAdOx1 nCov-19 or BNT162b2 in the UK (COV-BOOST): a blinded, multicentre, randomised, controlled, phase 2 trial. The Lancet. 2021;398:2258-2276.
4. Phase II/III Study of AZD2816, for the Prevention of COVID-19 in Adults [Online]. Available at: [Last accessed: January 2022].