Updated recommendations by the WHO Strategic Advisory Group of Experts on the use of ChAdOx1-Sbased (recombinant) COVID-19 vaccines


On 30 July 2021, the World Health Organization (WHO) released interim recommendations by the Strategic Advisory Group of Experts (SAGE) on the use of AstraZeneca's ChAdOx1-S (recombinant) vaccines (AZD1222, Vaxzevria,™ SII COVISHIELD). These vaccines are considered fully equivalent, even when produced at different manufacturing sites and assigned different product names; the recommendations therefore apply to all ChAdOx1-S-based (recombinant) vaccines. In summary, the updated findings were as follows: 

  • Second-dose considerations in supply-constrained settings: Countries that have not achieved high vaccination coverage rates in priority groups, and that have a high incidence of COVID-19 cases, along with vaccine supply limitations, may consider a period of up to 16 weeks before administration of a second dose.
  • Boosters: There is currently no evidence to indicate the need for additional doses, once an individual has received two doses.
  • Interchangeability with other COVID-19 vaccines: It is recommended that, for the two-dose vaccination schedule, the ChAdOx1-S [recombinant] COVID-19 vaccine should be used. In situations where supply is interrupted, a heterologous immunization schedule may be considered, using a ChAdOx1-S-based (recombinant) vaccine for the first dose, and an mRNA vaccine (BNT162b2 or mRNA-1273) for the second dose.
  • Precautions and contraindications: Cases of a very rare blood clotting disorder combined with a low platelet count, known as thrombosis with thrombocytopenia syndrome (TTS), has been reported, occurring between three and 30 days after vaccination with the ChAdOx1-S (recombinant) vaccine. A causal relationship between the vaccine and TTS is considered plausible, although the biological mechanism of this syndrome is still being investigated.

A number of cases of Guillain-Barré syndrome (GBS) have been reported after administration of the ChAdOx1-S (recombinant) vaccine; however, a causal relationship with the vaccine has been not been confirmed, though it has not been ruled out, and further studies are needed to assess a possible association. 


Available at: https://www.who.int/publications/i/item/WHO-2019-nCoV-vaccines-SAGE_recommendation-BNT162b22021.1

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