Real-world data shows increased reactogenicity in adults after heterologous compared to homologous prime-boost COVID-19 vaccination, March-June 2021, England

Adults receiving heterologous COVID-19 immunisation with mRNA (Comirnaty) or adenoviral-vector (Vaxzevria) vaccines had higher reactogenicity rates and sought medical attention more often after two doses than homologous schedules. Reactogenicity was higher among & 50 than ) 50 year-olds, women and those with prior symptomatic/confirmed COVID-19. Adults receiving heterologous schedules on clinical advice after severe first-dose reactions had lower reactogenicity after dose 2 following Vaxzevria/Comirnaty (93.4%; 95% confidence interval: 90.5-98.1 vs 48% (41.0-57.7) but not Comirnaty/Vaxzevria (91.7%; (77.5-98.2 vs 75.0% (57.8-87.9).

Automated summary

Adults receiving heterologous COVID-19 immunisation with mRNA or adenoviral-vector vaccines had higher reactogenicity rates, especially among those aged over 50, women, and individuals with prior symptomatic/confirmed COVID-19. Those who received heterologous schedules after severe first-dose reactions may have lower reactogenicity after the second dose, depending on the specific combination of vaccines used.