First Corona vaccine dose alone does not protect against the virus

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The first vaccination dose alone does not protect against infection with the coronavirus: With the first dose, the effectiveness in the 28 days until the second dose is only three percent and thus in the range of the statistical margin of error, as a study of the University of Chile found. By contrast, two weeks after the second vaccination, efficacy was 56.5 percent.

For their study, the researchers combined the efficacy of the Chinese vaccine Coronavac and Pfizer-Biontech’s vaccine. Coronavac is used in 93 percent of doses administered in Chile, which has one of the most advanced vaccination campaigns in South America. Its efficacy was 54 percent two weeks after the second vaccination, according to the study; Pfizer-Biontech’s efficacy is reported at 94 percent in an Israeli study.

According to the researchers, the efficacy of the first Coronavac dose was 27.7 percent after two weeks and continued to decline rapidly in the days leading up to the second dose. The study showed that the first dose “no longer had a relevant effect after four weeks,” University of Chile Rector Ennio Vivaldi said at a virtual press conference. Their recipients, he said, are basically just as susceptible to infection as non-vaccinated people.

Only those who get vaccinated twice can significantly reduce the risk of infection, Vivaldi added. The study estimates that there would have been 80 percent more cases of infection among people aged 75 to 79 without the vaccinations and 60 percent more among those aged 70 to 74.