First COVID-19 vaccine shot alone not protective: Chile study

A study in Chile, which has one of the furthest-advanced vaccination campaigns in South America — mainly with China’s Coronavac, found that a first dose alone does not protect against coronavirus infection.

The University of Chile study found inoculation to be 28 percent effective in protecting recipients within the first two weeks after the second dose, and 56 percent effective after the first two weeks.

But for a single dose, efficacy in the 28 days between the first and second dose was only three percent — on par with the margin of error in such studies, it said.

Researchers looked at the combined effect of Coronavac, which accounts for about 93 percent of doses administered, and the Pfizer vaccine. It estimated Coronavac’s efficacy in real-life conditions at 54 percent — in line with trial results in Brazil.

Chile has so far given at least one shot to seven million people, and both shots to four of 15 million inhabitants targeted for vaccination.

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