Mix and match?

Source: Lancet. 2021 Aug 6;S0140-6736(21)01694-9.

Contributed by Dr Prasanna Kumar, CMC Vellore

Mixing Vaccine got a shot in the arm with the Com-Cov trial which looked up immunogenicity and safety of mixing AstraZeneca -an adenoviral vectored vaccine (ChAd) and Pfizer–BioNTech- an mRNA vaccine (BNT). It is a participant-blinded, randomized, non-inferiority trial evaluating vaccine safety, reactogenicity, and immunogenicity of heterologous prime boosting over homologous prime boosting. The study included adults aged 50 years and older with no or well-controlled comorbidities and no previous SARS-CoV-2 infection by the laboratory from eight sites across the UK. 830 participants were enrolled and randomized, into 4 cohorts with various combinations of ChAd and BNT vaccines-(ChAd/ChAd, ChAd/BNT, BNT/BNT, and BNT/ChAd). Results for 463 participants with a 28-day prime-booster currently available. At day 28 post-boost, the geometric mean concentration of SARS-CoV-2 anti-spike IgG in ChAd/BNT recipients was non-inferior to that in ChAd/ChAd. But the study did not show non-inferiority of the heterologous schedule (BNT/ChAd) against the homologous schedule (BNT/BNT). Overall, BNT/BNT schedule was observed to be highly immunogenic, while ChAd/BNT had a high cellular immune response and ChAd/ChAd was least immunogenic but proven efficacious in preventing serious covid. Heterologous prime boosting schedule –ChAd/BNT and BNT/ChAd were both immunogenic but there was increased reactogenicity and there was no major adverse event related to immunization. Thus this study demonstrates it’s not only safe to mix vaccines but also effective as they are proven immunogenic as comparable to homologous prime boosting with reasonable numbers and two technically different vaccines –one is mRNA while the other is viral vector vaccine.