Pfizer and AstraZeneca, six different vaccines used as anti-Covid boosters were found to be safe and elicited strong immune responses in people previously vaccinated with a two-dose course of the Oxford and BioNTech vaccines. This is what emerges from the first randomized trial of boosters given after the two doses of these two vaccines. Published in ‘The Lancet’, the work takes into consideration 7 different boosters: Oxford-AstraZeneca, Pfizer / BioNTech, Novavax, Janssen (J&J), Moderna, Valneva and Curevac (CVnCov). All 7 vaccines, used for the third dose 10-12 weeks after the primary course, increased immunity after the Oxford-AstraZeneca course; 6 out of 7 – that is, all but Valneva – increased it after the Pfizer / BioNTech cycle.
There are “large variations in cellular and antibody immune responses between vaccines,” explain the authors of the phase 2 study.. The UK research involved 2,878 adults aged 30 and over, with around half aged 70 and over. The two vaccines considered as primary courses are very popular: AstraZeneca in more than 180 countries and Pfizer in more than 145. The two doses showed protection of 79% (Az) and 90% respectively after 6 months in different studies. (Pfizer) with respect to hospitalization and death. However, protection against Covid-19 infection wanes over time. This has led to boosters being considered. Hence the study.
“E’ very encouraging that a wide range of vaccines, using different technologies, show benefits as a third dose for AstraZeneca or Pfizer-BioNTech – observes Saul Faust, head of the trial, University Hospital Southampton NHS Foundation Trust -. This gives confidence and allows flexibility in the development of recall programs. ”
The expert points out that the results of the study refer “only to these vaccines as a booster to the two primary vaccinations and the immune response they drive 28 days” after the injection. “Further work will generate data 3 months and one year after people have received their boosters, and will help understand the impact on long-term protection and immunological memory.”
Among the study limitations it is reported that the interval between the second and third dose was shorter in some participants, compared to the first two doses. Several studies have shown that a longer period of time between the first and second doses can improve immunogenicity, including better antibody responses, when starting doses of Pfizer vaccine are 12 weeks apart instead of 3 weeks. This could mean that the increase in immunity is less than it would have been if longer dose intervals had been used.