Technical note on delayed shipments for the ChAdOx1-S [recombinant] vaccines: what are the implications for the administration of second doses?

Overview

The global supply of ChAdOx1-[recombinant] vaccines is presently constrained, which impacts country access to ChAdOx1-S [recombinant] vaccine (AstraZeneca COVID-19 vaccine AZD1222, SII Covishield, SK Bioscience). This constraint is due to multiple factors including company related production delays, shipping delays and specific unforeseen country needs. This document supplements information provided in a technical note entitled ‘Considerations for optimizing deployment of ChAdOx1-S [recombinant] vaccines in a time-limited constrained supply situation’ (see link below) and provides updated information relevant to the provision of a second dose in the current limited supply context. While definitive evidence is not currently available, the considerations below are based on expert review of the best available evidence and are designed to assist countries in making choices supported by previous WHO guidance. This technical note has been developed by the WHO secretariat and has been reviewed by members the Strategic Advisory Group of Experts on Immunization (SAGE) and SAGE working group on COVID-19 vaccines. It is not an official WHO policy recommendation.