Raquel Portugal/Fiocruz Imagens
With the vaccination closer and closer, there is still a portion of the population with doubts about the effectiveness of the immunizer. According to the World Health Organization (WHO) and ANVISA, the recommended general efficacy is at least 50%. This means that, in order to be released by the regulatory agencies in each country, vaccines need to reach this percentage.
The overall efficacy rate represents the proportion of case reduction among the vaccinated group compared to the non-vaccinated group. That is, if a vaccine has 90% efficacy, it means that 90 out of 100 vaccinated people are protected from the disease. The other 10 might get sick and present mild symptoms.
Tests take place, first of all, on animals. If the vaccine has good results, tests on humans begin, involving four phases. The first two phases measure the immune response and, from the third phase on, efficacy is measured by one group of people receiving a placebo, and another one receiving the dose of the vaccine.
If the immunizer is safe and effective, there will be more cases of the disease in the placebo group and ideally almost none in the vaccinated group. Each time a volunteer gets sick, it is counted an “event”.
From this, it takes a certain number of events to achieve the appropriate statistic in order to make the comparison between groups. This difference between the numbers is the indicator of effectiveness.
Phase four is marked by continuous surveillance and is triggered as soon as the vaccine has already been approved for use in the population. It is at this moment that it is possible to measure the vaccine real ability to avoid the disease, outside the controlled environment of laboratories.
Currently, most vaccines that are being manufactured in Brazil have 100% efficacy in the most severe cases and in hospitalizations. Thus, the population that is immunized and yet develops the disease will present only the mildest symptoms.
Oxford-AstraZeneca vaccine has a 70% efficacy
According to the coordinator of clinical trials of the Oxford-AstraZeneca vaccine in Brazil, Sue Ann Costa Clemens, the vaccine developed by the university has a 70% efficacy already in the first dose. The second dose will be given initially after three months, raising the efficacy to over 80%.
The time interval between doses is longer than initially expected, and it can protect a number of people more quickly. This is because, while the first doses are being used, Fiocruz will be producing other supplementary ones.
The technology used by Oxford-AstraZeneca is that of a viral vector, which uses a genetically modified virus to penetrate human cells and discharge genetic instructions to produce SARS-COV-2 proteins. When perceived by the immune system, antibodies are produced.
