Mar 06, 2021 Volume 397 Number 10277 p853-940
Single-dose Oxford–AstraZeneca COVID-19 vaccine followed by a 12-week booster
Ivan F N Hung, Gregory A Poland
… Important study limitations include the fact that these studies were not prospectively designed to establish whether vaccine efficacy would differ by dose interval; therefore, these post-hoc exploratory findings could be biased. Other limitations are that participants were not randomised to dosing interval, only one of the four trials was double-blind, and the single-dose recipients were self-selected. Furthermore, baseline characteristics between the single-dose and two-dose cohorts were substantially different, with an older median age, higher proportion of men and non-white participants, and a smaller proportion of health or social care workers in the two-dose cohort than in the single-dose cohort. Also, worth considering is whether these results would hold up with widespread circulation of more transmissible and lethal viral variants.
Overall, the value of this study is in providing evidence that a single dose of the ChAdOx1 nCoV-19 vaccine is highly efficacious in the 90 days after vaccination, that a longer prime-boost interval results in higher vaccine efficacy, and that protection against symptomatic COVID-19 is maintained despite a longer dosing interval. It offers much-needed evidence for the UK policy of extending the dosing interval to 12 weeks and for rapid mass-immunisation campaigns worldwide. Further studies are warranted to assess whether a longer-interval strategy would also offer higher vaccine efficacy against the new variants8 and could be applicable to other types of COVID-19 vaccines. 9, 10, 11