In this article the authors assess 88 health care workers who had received one dose of ChAdOx1 nCoV-19 vaccine 9 to 12 weeks earlier. Among these participants, 37 chose a homologous boost with ChAdOx1 nCoV-19 and 51 chose a heterologous boost with mRNA-1273 (Moderna). Blood specimens were obtained at the time of boost, 7 to 10 days after the boost, and 30 days after the boost. On the day of the boost, the two groups had similar levels of SARS-CoV-2 S-specific and receptor-binding domain (RBD)-specific IgG and neutralizing antibodies. Levels of S-specific and RBD-specific IgG at 7 to 10 days after a ChAdOx1 nCoV-19 boost were 5 times as high as on the day of the boost (P<0.001); at 7 to 10 days after an mRNA-1273 boost, levels of S-specific IgG were 115 times as high and levels of RBD-specific IgG were 125 times as high as on the day of the boost (P<0.001). After 30 days, levels of S-specific IgG remained similar to those at the 7-to-10-day time point in both groups. The authors concluded that the mRNA-1273 vaccine can efficiently stimulate the SARS-CoV-2–specific B-cell memory that has been generated by a prime dose of ChAdOx1 nCoV-19 vaccine 9 to 12 weeks earlier and that it may provide better protection against the B.1.351 variant than a ChAdOx1 nCoV-19 boost. These data also suggest that mRNA vaccines (here in the form of mRNA-1273) may be useful for vaccination strategies in which a third dose is to be administered to persons who have previously received two doses of ChAdOx1 nCoV-19.
Normark J, Vikström L, Gwon YD, Persson IL, Edin A, Björsell T, Dernstedt A, Christ W, Tevell S, Evander M, Klingström J, Ahlm C, Forsell M. Heterologous ChAdOx1 nCoV-19 and mRNA-1273 Vaccination. N Engl J Med. 2021 Jul 14. doi: 10.1056/NEJMc2110716.