Effectiveness of the vaccination program in Chile: a single dose does not protect, but 14 days after the second dose protection against contagions is 56%

How protected are people who are vaccinated against Covid-19 to get the virus? That was the question that motivated the first research on the effectiveness of the vaccines with which the population is being inoculated today.

Unlike the data from clinical studies available until now, this first National study that estimates the effectiveness of the Government’s vaccination program on Covid-19 infections carried out by academics from the University of Chile, it was carried out in the general population and with real numbers of infected and vaccinated people delivered by the health authority, so it is the first concrete data, in an uncontrolled environment, but in the reality of the moment pandemic that is currently being experienced in the country.

The results are positive and they are in the same line of the knowledge that was already had of the vaccines: a dose almost does not protect against new infections but those who have the two doses of vaccine and more than two weeks since the last inoculation have a 56% lower risk of getting it virus Sars-CoV-2 if they come into contact with him.

The study was carried out by the researchers Alejandro Jofré, researcher at the Center for Mathematical Modeling of the University of Chile, Eduardo Engel and Juan Díaz.

The rector of the University of Chile, Ennio Vivaldi, He stressed that this is encouraging data considering the impact that has been had on the population that already has a vaccination time and that shows the effectiveness of vaccines in the prevention of infections.

For the study, they divided the study population into three groups: those who have received a single dose, those who received two doses but still do not complete 14 days after the second inoculation, and those who have both doses and who have been in for more than two weeks. since the last inoculation.

The academic, Eduardo Engel, explains that the data of the vaccinated people were taken up to March 29 and whose data were obtained from the Github del Ministry of Science, and with them the effectiveness of the program was estimated according to age group, new cases and number of vaccinated.

According to this data crossing, the Estimated effectiveness in the group with two doses and more than 14 days from the last inoculation, reaches 56.5%. In those who have two doses but do not reach two weeks from the last vaccine, the effectiveness against contagion is 27.7% and among those who have only one dose, the effectiveness barely reaches 3%, almost as if they had no protection.

From these data, the effectiveness of the vaccine Sinovac which is the vaccine with which almost 94% of people have been inoculated, says Engel. If the difference between the two vaccines is corrected, the effectiveness in protecting against infections of the Coronavac vaccine It is 54%, the researchers estimate, a figure higher than that found in the study that carried out the study of the Instituto Butantan in Brazil it was 50.3%.

FILE PHOTO: A booth displaying a coronavirus vaccine candidate from Sinovac Biotech Ltd is seen at the 2020 China International Fair for Trade in Services (CIFTIS), following the COVID-19 outbreak, in Beijing, China September 4, 2020. REUTERS/Tingshu Wang//File Photo

This similarity between the figures from this study and the Brazilian one is encouraging, Engel highlights, as it suggests that the effectiveness of the Sinovac vaccine has not been affected by a possible circulation of new variants of the virus in the country, either because said circulation is still It is not massive or because the vaccine does not lose effectiveness with these variants.

In the opinion of Pablo González, researcher at the Catholic University and from Millennium Institute of Immunology and Immunotherapy (IMII) Y executive director of the clinical study carried out in the country with the Sinovac vaccine, these results are positive, “however, given the progress of the vaccination campaign and the growing number of individuals who have been vaccinated, it is expected that the short term, different effectiveness analyzes will emerge based on different mathematical models, but also based on new epidemiological data ”.

González highlights that this is one of the first analyzes and therefore, “the results must be considered with caution and as a first estimate, since they are preliminary and do not include other fundamental parameters, such as consultations for symptoms, hospitalizations and deaths.”

In addition, the IMII researcher highlights that vaccines mainly prevent disease and to some extent symptomatology, but not contagion. “For now, the analysis presented today is a first, preliminary estimate of the effectiveness of the vaccine, limited to some specific age groups, and considers data as of today, so it constitutes to some extent an analysis based on a photograph of the moment”.

Photo: Reuters

Even though to date there is a significant proportion of the population that has not yet received the two doses of the vaccine, “the data are globally very positive and it is expected that the effectiveness will be progressively greater when analyzing the reduction in hospitalizations and deaths. ”.

As the age group that has been immunized the longest are the elderly, there are some differences in the protection that vaccination provides according to age.

In those over 80 years of age, the first vaccinated at the beginning of February, it is observed that vaccination has positive effects: if they had not been vaccinated, in the last days the infections would have been 60% more. In the group of people between 74 and 79, the protection is 80%, that is, without vaccination, 80% more people would have been infected than those who have actually been infected in recent weeks. In the younger groups, this difference is less because they do not have been vaccinated as long.

Chancellor Vivaldi and the researchers asked the authorities to allow access to more data and greater data specificity in order to better understand how vaccines are working. In this way, they asked to be able to have access to the disaggregated data (vaccinated or not vaccinated and with how many doses) of the people who are infected, those who present symptoms, who are in the ICU and also those who die.

As announced by Ministry of Health , next week they will release another effectiveness analysis, and according to González, this will probably consider effectiveness parameters around hospitalizations, an element that the researcher considers “extremely relevant for the control of the health emergency we are experiencing.”

These results give us a glimmer of hope, but we must be empathetic, take care of ourselves, wear masks, follow sanitary measures, stay at home even with the vaccine. Only then will we get out before the pandemic ”. And, he added that “the vaccine only has one result, a significant contribution when 14 days have passed since the second dose and that reinforces the idea that getting vaccinated at least until that time has passed, does not have an important effect and does not it should in no case be considered a factor to neglect everything that has been said regarding measures to prevent contagion ”, insists the rector of the University of Chile.

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