I midten af [[december]] anbefalede [[WHO]] at kombinere vektor-baseret [[COVID-19-vaccine]] med med mRNA-vaccine for øget effekt (for eksempel AstraZeneca kombineret med Pfizer).<ref>{{cite news |url=https://thainews.prd.go.th/en/news/detail/TCATG211218144610815 |title=Virologist Recommends Mixing and Matching COVID Vaccine |work=[[National News Bureau of Thailand]] |date=18. december 2021 |access-date=19. december 2021 |language=en}}</ref><ref>{{cite news |url=https://www.reuters.com/business/healthcare-pharmaceuticals/who-makes-interim-recommendations-mixing-matching-covid-19-vaccines-2021-12-16/ |title=WHO makes interim recommendations for mixing and matching COVID-19 vaccines |work=[[Reuters]] |date=16. december 2021 |access-date=19. december 2021 |language=en}}</ref><ref>{{cite web |url=https://www.who.int/publications/i/item/WHO-2019-nCoV-vaccines-SAGE-recommendation-heterologous-schedules |title=Interim recommendations for heterologous COVID-19 vaccine schedules |work=[[WHO]] |date=16. december 2021 |access-date=19. december 2021 |language=en}}</ref>
Vira