Vaccine effect: study by the University of Chile reveals effectiveness of up to 56.5% after the second dose

A study carried out by researchers from the University of Chile revealed that the effectiveness of the COVID-19 vaccine is 56.5% to prevent infections in those who have received the second dose.

The research of Juan Díaz, Eduardo Engel and Alejandro Jofré calculated this number taking into consideration that the vaccines currently applied in Chile are Sinovac (93% of the second dose administered) and Pfizer BioNTech (7% remaining) and is taken in account that the latter has shown an effectiveness of 94% in Israel.

Likewise, it is concluded that the effectiveness of the Sinovac vaccine in preventing infections is approximately 54%, both of people with one dose and those who have already completed the process with its two doses, a value similar to the 50.4% reported by the Butantan Institute in the efficacy study of this vaccine carried out in Brazil, which was key to the approval of this vaccine by the ISP in Chile. This means that the circulation of new variants in the country is limited for now or that the Sinovac vaccine maintains its effectiveness with these variants, the researchers note.

The researcher from the University of Chile, Eduardo Engel, specified that “the methodology we use, given the information available, estimates the combined effect of what has been applied from Sinovac and Pfizer and is 56.5% and then, taking the effectiveness of Pfizer in Israel, we can infer 54% for Sinovac ”.

The study carried out with public information from the Ministry of Science, distinguishes between three groups of vaccinated: those who have received only one dose, those who received a second dose less than two weeks ago and those who have received the second dose at least two weeks ago. The estimated efficiencies are 3.0%, 27.7% and 56.5%, respectively.

The study confirms that with a single dose the protection against infections is very low, 3%. Hence the importance of receiving the second dose and continuing with strict care until at least two weeks after its application.

The researchers also emphasize that it should not be forgotten that the degree of protection against infections is 56%, not 100%, and that at the moment there is no information necessary to evaluate the effectiveness of the vaccination program to prevent hospitalizations. “Although it is expected to be higher, information is needed to confirm that this is the case,” said Alejandro Jofré.

The rector of the University of Chile, Ennio Vivaldi, stressed that it is important to be informed in a correct and timely manner of the measures that are being taken to prevent the spread of the virus. “These results give us a light of hope, but we must be empathetic, take care of ourselves, wear masks, follow sanitary measures, stay home even with the vaccine. Only then will we get out before the pandemic ”.

He added that “the vaccine only has one result, a significant contribution 14 days after 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 should not in no case be considered a factor to neglect everything that has been said regarding the measures to prevent contagion ”.

Along the same lines, Eduardo Engel maintains that with the aforementioned background, “it is vitally important to redouble government efforts, both in actions and in risk communication, and also among citizens to prevent the spread of the virus.”

For his part, Juan Díaz said that “it is very important to have information to carry out a similar study to measure the effectiveness of the vaccination program in preventing hospitalizations.”

Likewise, the study’s figures indicate that the challenge of achieving herd immunity will be greater in Chile than in countries that are applying vaccines more effectively. Therefore, the authors called for reinforcing the vaccination campaign that is underway today, making a special effort to vaccinate all the laggards. In addition to maintaining prevention measures such as the use of masks, hand washing, social distancing, as well as the quarantine measures applied to reduce the real mobility of people throughout the country.

The analysis is based on how vaccines are working in reality, not in clinical trials, and applies a non-linear version of the difference methodology to obtain a rigorous and accurate estimate of the effectiveness of the vaccination program in preventing infections.

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