Current homologous vaccine schedules including Vaxzevria® are proven highly effective against COVID-19 hospitalisation and severe disease including that caused by the Alpha and Delta variants.
While there are no immediate serious safety concerns with heterologous vaccine schedules, accumulating data indicates that the rates of side effects following the second dose may be higher, particularly when administered with the shorter four-week interval between doses. The longer-term safety profile remains to be assessed. Further monitoring is required to determine the overall safety profile of these schedules.
Early studies indicated that these heterologous combinations are highly immunogenic. A heterologous vaccine schedule is more immunogenic that homologous Vaxzevria® but not more immunogenic that a homologous Comirnaty® schedule. For those primed with Vaxzevria®, an mRNA vaccine as the second vaccine dose can result in excellent humoral and enhanced cellular immunity. Given that all the tested homologous schedules, including Vaxzevria®, are proven to be highly effective against severe COVID-19, it is likely that the heterologous schedule will also prove to be effective. However, as yet clinical effectiveness data is lacking. It remains to be proven that the augmented immunogenicity translates into better effectiveness against COVID-19.
Given the impact of the Delta variant and the rapidly rising case numbers there is an urgency to get everyone vaccinated as safely and as quickly as possible. Available evidence supports the selective use of heterologous vaccination schedules to maximise vaccine uptake.
- Recommendation
- Europe
- Ireland
- COVID-19
