Weighing the Timing of the Oxford/AstraZeneca Vaccine's Second Dose

Because the need to rapidly immunize the population against SARS-CoV-2 must be balanced against vaccine scarcity, delaying the second dose of any two-dose vaccine has been suggested. However, few data support any change in the recommended prime-boost intervals, which range from ≤6 weeks (WHO) to ≤12 weeks (U.K. and Canada). Investigators analyzed pooled data from four trials in the U.K., Brazil, and South Africa to examine the effects on immunogenicity and efficacy of extending the interval between the first and second doses of the Oxford/AstraZeneca adenovirus-vectored vaccine, AZD1222.

Among 17,178 participants, vaccine efficacy in preventing virologically confirmed symptomatic COVID-19 ≥14 days after the second dose was 66.7%, with no hos…