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February 19, 2021 The AstraZeneca vaccine is effective: 81% if the second dose is administered 3 months after the first and 55% if the booster is given within 6 weeks.
Furthermore, a single dose in the first 3 months after administration gives 76% immunity once 22 days have elapsed after injection.
These are the results of an analysis conducted on the data of the phase 3 trial which involved 17,178 participants over 18 in Great Britain, Brazil and South Africa, published in "The Lancet".
A. The study also includes updated estimates of the overall efficacy of two standard doses of the vaccine against symptomatic disease, confirming that 22 days after the first dose there were no hospitalizations or deaths among those receiving the vaccine compared to 15 cases in the group. control.
According to the authors of the research, these results give validity to the method of lengthening the interval between the first and the second dose as occurs in the United Kingdom and also suggested by the World Health Organization.
Given the lack of vaccines, according to the researchers, it is appropriate to give the first dose to more people immediately and also to guarantee the second.
"The supply of vaccines is likely to be limited in the short term," explains lead author Andrew Pollard of the British University of Oxford.
In this scenario, "policy decisions are important. In an emergency, multiple people could initially be vaccinated with a single dose to give immediate protection."
However, the researcher points out, "it is important that the second dose is given in the long term to ensure long-lasting immunity."
Indeed, the researchers point out that "it is not yet clear how long the protection of a single dose of vaccine can last, because the results of the study are limited to a maximum of 3 months".
For this reason the second dose is still recommended.