Combining vaccines

Four studies (not yet peer reviewed) posted this week show that a first dose of the AstraZeneca vaccine followed by a second dose of the Pfizer vaccine is well tolerated and induces potent humoral and cellular responses. Three of the studies (one from Spain, and two from Germany) did not include a comparison group vaccinated with two doses of AstraZeneca, but a fourth small study (also in Germany) did. This study showed that heterologous vaccination led to a significant 11.5-fold increase in anti-Spike IgG, as compared to the 2.9-fold increase after homologous AZ/AZ vaccination. It also induced significantly higher frequencies of Spike-specific CD4 and CD8 T cells and, in particular, higher titers of neutralizing antibodies against the B.1.351 (beta) and the P.1 (gamma) variants of concern.