The Chilean president announced that, starting next week, Chile will start applying a booster dose to those vaccinated with CoronaVac, whose effectiveness drops considerably six months after the first dose.

The lower effectiveness of the Chinese immunizing agent, applied massively in Chile, Uruguay and Brazil, has led neighboring governments to choose to replace CoronaVac.

Considering the evolution over time and the risk of the Delta variant, in addition to receiving (scientific) recommendations both nationally and internationally, we decided to start a booster vaccination for all people who received two doses of Sinovac vaccine [laboratório chinês da CoronaVac]”, announced President Sebastián Piñera, during the delivery of the government’s balance sheet on the pandemic.

The third dose will be applied, in a staggered way, from the next August 11th in people over 55 years old. The schedule includes those vaccinated with the second dose of the Chinese immunizing agent between the 1st and 14th of March. This group will preferably receive a dose of AstraZeneca.

The Undersecretary of Health, Paula Daza, added that “children under 55 years should start to be vaccinated in September with the Pfizer vaccine through a schedule to be defined according to the availability of the arrival of vaccines”.

Immunodeficient people over 16 who have been vaccinated with the two doses by May 31 will also be vaccinated, but with Pfizer’s vaccine. This segment has difficulty in producing antibodies, having as its only alternative a messenger RNA vaccine.

All adults who received CoronaVac will be vaccinated”, guaranteed Pinera.

Currently, 12.6 million people are fully vaccinated in Chile in one of the most successful campaigns in the world whose goal is to reach at least 15.2 million people, equivalent to 80% of the population.

CoronaVac, responsible for 70% of vaccination in Chile, has been shown to be effective against the coronavirus in severe cases, but in symptomatic cases its effectiveness decreases considerably from the sixth month after the first dose is applied.

A week ago, the Ministry of Health of Uruguay also announced a third dose of Pfizer for those vaccinated with the Chinese CoronaVac. This third dose will be applied to those who have at least 90 days since the application of the second dose of the Chinese immunizing agent. Enrollment in the booster calendar started this week.

On Wednesday (04), the Ministry of Health of Chile released the study “Effectiveness of the Vaccination Program against SARS-CoV-2”, carried out between February and July, through which it compares the effectiveness of immunization agents from Sinovac laboratories (CoronaVac ), Pfizer-BioNTech and AstraZeneca. In the case of CoronaVac, the effectiveness of 67% drops to 58.49% in symptomatic cases.

All remain effective for the prevention of the most severe forms of the disease, but suffer a decrease in effectiveness in symptomatic cases.

It is very likely that this decrease in effectiveness against symptomatic covid-19 will continue over time. Therefore, we are at a good time to make the decision to reinforce it”, recommended Dr. Rafael Araos, one of the study leaders.

Two weeks ago, Chilean scientists at the Catholic University of Chile, who conducted a clinical trial with 2,300 volunteers, proved the vaccine was highly effective during the first six months to prevent serious cases and deaths, but found a significant drop in effectiveness after that period.

On April 16, Chile’s Ministry of Health published a study of 10.5 million Chileans vaccinated 14 days after the second dose of CoronaVac. Vaccine effectiveness was 67% (mean range 65% to 69%) to prevent symptomatic covid-19.

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