Interim recommendations for heterologous COVID-19 vaccine schedules

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This interim guidance pertains to heterologous primary and heterologous boosting schedules of Covid-19 vaccines. It focuses on heterologous schedules combining multiple vaccine platforms (e.g. a vectored vaccine followed by an mRNA vaccine).

Summary of the recommendations:

WHO supports a flexible approach to using either homologous (single platform) or heterologous (mix and match) vaccination schedules.
SAGE considers two doses of any WHO EUL COVID-19 vaccine to be a complete primary series, with consideration of dosing order according to WHO’s recommendations.
SAGE has made specific recommendations for countries considering heterologous schedules, to ensure an equivalent or favourable immunogenicity or vaccine effectiveness:
- Countries implementing WHO EUL inactivated vaccines for initial doses may consider using WHO EUL vectored or mRNA vaccines for subsequent doses, depending on product availability;
- Countries implementing WHO EUL mRNA vaccines for initial doses may consider using WHO EUL vectored vaccines for subsequent doses, depending on product availability.
- Countries implementing WHO EUL vectored vaccines for initial doses may consider using WHO EUL mRNA vaccines for subsequent doses, depending on product availability.
Many countries face severe vaccine supply constraints, combined with a high disease burden. The interim recommendations would allow for flexibility within national immunization programmes. Either homologous or heterologous should be utilized to achieve high coverage of priority groups in as timely a manner as possible.

The full text of the interim recommendations is available here:

https://www.who.int/publications/i/item/WHO-2019-nCoV-vaccines-SAGE-recommendation-heterologous-schedules