Study in Chile: How effective are vaccines to prevent infections?

SANTIAGO, Chile.- A study on the Vaccination against Covid-19 in Chile showed 56.5% effectiveness in preventing new infections two weeks after the administration of the second dose and pointed out that a single dose does not protect against infection by the coronavirus.

The work, carried out by the University of Chile, considers the combined effect of the two vaccines currently applied in Chile: that of the Chinese pharmaceutical Sinovac, which represents 93% of the doses administered to date, and that of the American Pfizer (in collaboration with the German company BioNTech).

The data is known when Chile has 7.07 million people vaccinated with at least one dose and 4.04 million who have received both. With these numbers 26.6% of the target population of the campaign is vaccinated (15.2 million out of a total of 19 million inhabitants of the country).

The data positions Chile as one of the greater speed of vaccination of its population in Latin America and the world, in a process that is taking place alongside a sustained increase in new coronavirus infections, with a daily record number of infections exceeding those of the first wave, with more than 8,000 new infections per day.

The study establishes three conclusions on the effectiveness in preventing new infections: deliver a 56.5% for people who finished more than two weeks after receiving both doses; a 27.7% for those who also received both doses, but still have not exceeded 14 days after the last application, and only one 3% (equal to the margin of error) for those who have received a single dose.

“Getting vaccinated very significantly reduces the possibility of infection; it does not eliminate it but it reduces it a lot, so you have to be vaccinated ”, declared the rector of the University of Chile, Ennio Vivaldi, during the virtual press conference during which the results of this first study were presented.

Another message is that “The first dose of the vaccine has no significant effect after four weeks.” Therefore, six weeks after being vaccinated “for all practical purposes, one is in the same vulnerable situation to contagion from a person who had not been vaccinated,” he added.

The results are particularly conclusive in the curves of new infections of people over 70, most of whom have already completed the vaccination regimen, after a process that began en masse in Chile on February 3.

The study calculates that between the ages of 75 and 79, 80% more infections would have been generated if the vaccine had not been applied. The percentage drops to 60% for ages between 70 and 74.

Doubts about collective immunity

Study estimates for the vaccine Sinovac an efficiency of 54%, in line with the results reported by the Butantan Institute of Brazil. For that of Pzifer / BioNTech, data provided by Israel with 94% efficiency was taken into account.

The similarity between the figures from the Chilean and Brazilian study on the efficacy of the Sinovac vaccine is an encouraging result for Chilean researchers.

This suggests that it has not been affected by a possible circulation of new variants of the virus in Chile, either because this circulation is not yet massive, or because the vaccine does not lose efficacy with these variants.

The study, which was carried out on the basis of public information from the Chilean Ministry of Science, However, he could not determine to what extent the vaccines applied in Chile are or are not being used to prevent hospitalizations due to the coronavirus., because there is still no cross-referencing of data between people vaccinated and those admitted to hospitals.

“Although it should be higher, information is needed to confirm that this is the case,” said one of the study’s authors, Alejandro Jofré.

The study also indicates that based on the efficacy of the Sinovac vaccine, the challenge of obtaining collective immunity – promised by the Chilean government towards the end of June – is even greater.

“Achieving herd immunity will be a greater challenge than achieving it in countries with vaccines that are on average more effective.“Said Eduardo Engel, another of the research authors, explaining that the less effective a vaccine is,” a larger fraction of the population needs to be immunized. “

The goal of the Chilean government is to vaccinate 15.2 million people (80% of the total population of the country) by June 30.

Agencia AFP

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