A Swedish study, which was just published in The Lancet on October 17, investigated the effectiveness of heterologous prime-boost vaccination against COVID-19 (AstraZeneca viral vector-based vaccine-prime, Pfizer-BioNTech or Moderna mRNA vaccine-boost) (Nordström et al., 2021). From a Swedish cohort in which individuals received 2 doses of COVID-19 vaccines (N = 3,445,061), Nordström et al. (2021) selected 94,569 people who had been vaccinated with heterologous AstraZeneca viral vector-based vaccine-prime/Pfizer-BioNTech mRNA vaccine-boost, 16,402 individuals with heterologous AstraZeneca viral vector-based vaccine-prime/Moderna mRNA vaccine-boost, 430,100 subjects with homologous AstraZeneca vaccine-prime/AstraZeneca vaccine-boost, 2,065,831 with....