The vaccines Coronavac, from the Sinovac laboratory, and from Pfizer-BioNTech lost effectiveness to prevent symptomatic covid-19, but maintain the protection to prevent serious cases, according to a study by the Chilean government, one of the countries with the highest rate of vaccination.
The result reinforces the need to apply a third dose.
According to the new study of the effectiveness of the vaccination program initiated by the Ministry of Health of Chile – which managed to immunize with two doses about 65% of the population -, the effectiveness of the Coronavac vaccine, the most used in the country, dropped to 58.49% to avoid symptomatic cases.
In April, the official study reported an effectiveness of 67%, while on June 26, the Ministry of Health reported that it had fallen between 63% and 64%.
As for Pfizer, which, as it is less applied in the country, had not been considered in previous studies, it had a reported efficacy of 87.69%. International studies have previously placed it above 90%.
However, both Coronavac and Pfizer’s immunizers maintain protection against the development of severe cases of the disease.
“Protection against covid infection drops, but protection against the most important outcomes remains,” Rafael Araos, adviser to the Chilean Ministry of Health, said at a press conference on Tuesday, as he presented the study six months after the start of the mass vaccination.
For Coronavac it was registered 86.02% of effectiveness to prevent hospitalizations; 89.68% for admission to Intensive Care Units (ICUs) and 86.38% for deaths.
For Pfizer, there was 97.15% effectiveness in preventing hospitalizations; 98.29% for admission to ICUs and 100% for deaths.
– Uncertainties about the delta variant –
Chile, which started mass vaccination on February 3, managed to vaccinate 80% of its target population (15.2 million out of a total population of 19 million).
This Tuesday, the country registered 616 new cases, the lowest figure since April last year.
“These data reinforce that vaccination has played an important role in the control of the pandemic and, although we see some ‘red flags’ regarding the decrease in the effectiveness of Coronavac and Pfizer, this has not been reflected so far in the most serious outcomes,” added Araos .
The decrease in protection and the uncertainty caused by the circulation of the delta variant, which is much more contagious, opened the debate on the application of a third booster dose.
Uruguayan authorities, with a vaccine scheme similar to the Chilean one, have already approved the third dose with Pzifer for those who received the two doses of Coronavac.
However, the fact that protection is maintained for the most severe cases indicates that people are able to produce antibodies to fight the disease.
“Although the antibodies fall and this allows more infections to occur, the body is able to respond quickly with a new production of antibodies,” Araos said.
The expert hopes that effectiveness will continue to decline, as with other vaccines against respiratory viruses.
“I would expect it to continue falling slowly or remain as we’ve seen so far, unless delta becomes more prevalent and (vaccines) have a lesser response and maybe we could see a faster fall. This is the uncertainty that delta brings us to any kind of forecast,” he added.
+ Learn about the effectiveness of each vaccine against Covid-19