So far studies have shown that one dose of the currently available COVID-19 vaccines, whether it be Moderna's mRNA 1273, Pfizer-BioNTech's BNT162b2 (Comirnaty) or Oxford-AstraZeneca AZD1222, offer varying levels of protection. Ranging mostly from 50% to 66%, the first doses provide a substantial boost compared to non-inoculated populations, but real protection comes after the second dose with figures showing a 70% or above effectiveness.
Having said that, studies are showing that the first shot of two vaccinations with the BioNTech or AstraZeneca vaccines already significantly reduces the risk of infection with coronavirus, which is the reasoning behind the U.K's 12-week vaccination window for the second dose. Turkey also recently extended the interval between two doses of the BioNTech vaccine, increasing the 28-day gap to about six to eight weeks.
What's been promising about the first dose is that this protection also applies to the more infectious B.1.1.7 variant first discovered in Kent, England, according to a large-scale study by the University of Oxford in cooperation with the British statistics authority ONS and the country's Health Ministry.
Regardless of whether the BioNtech or AstraZeneca vaccine is given, the risk of coronavirus infection fell by 65% three weeks after vaccination, the university said, announcing its findings on April 23.
The number of symptomatic COVID-19 infections even decreased by 72%. For the study, which has not yet been published in a scientific journal, the test results of about 370,000 people from the period between December 1 and April 3 were taken into account. Both vaccines proved to be just as effective against the British variant B.1.1.7 as against the original type discovered in the first wave.
The effectiveness of the vaccines also did not change depending on the person's age or state of health.
"The protection from new infections gained from a single dose supports the decision to extend the time between first and second doses to 12 weeks to maximize initial vaccination coverage and reduce hospitalizations and deaths," said Koen Pouwels, one of the Oxford University scientists involved.
However, the new analysis also suggests that vaccinated people could pass on the infection, though up to a limited extent. This is evident from the fact that the number of asymptomatic cases is not reduced to the same extent as the number of cases of the disease, he said.
"This emphasizes the need for everyone to continue to follow guidelines to reduce transmission risk, for example, through social distancing and masks," Pouwels said.