October 25-31 2021
Is it more effective to combine different vaccines?
There are a number of different anti-COVID-19 vaccines currently available. Rare but serious side effects have been reported for the AstraZeneca (AZ) vaccine. Several countries have therefore decided to administer the Pfizer-BioNTech (PB) vaccine to people younger than 55 who have already had a 1st dose of AZ. Previous clinical studies have analysed the efficacy of these vaccines when the same is used for both injections. In this study, scientists investigated the efficacy of the combination of AZ for the first injection and PB for the second.
French researchers (at the University Claude Bernard in Lyon) compared the risks of infection in patients having received heterologous (AZ/PB) vaccination (2512 individuals) with those having received homologous vaccination with 2 doses of PB (10 609 individuals). In total, 10 cases of infection (0,40%) were noted in patients having received heterologous vaccination against 81 cases (0,76%) in individuals having received homologous vaccination. The AZ/PB vaccination therefore seems to give better protection against infection and is even more effective than 2 doses of PB.
The scientists then carried out tests on virus neutralisation by serum (which contains antibodies) from health professionals who had received either heterologous or homologous vaccination. The serum from patients with heterologous vaccination neutralised the SARS-CoV-2 viral particles more effectively. Finally, the scientists showed that heterologous vaccination enables more B lymphocytes (cells that manufacture antibodies) targeting the virus to be induced than homologous vaccination.
So vaccination with 2 different vaccines, AZ and PB, confers better protection than full vaccination with PB. Although these results need to be further studied over the long-term, heterologous vaccination may well be considered so as to provide better immunity in immunocompromised patients.