A study by the Covid-19 Action group shows that, with the current level of contamination, states need to vaccinate 22% to 83% of the population for the disease’s reproduction rate to fall, which means reversing the growth curve of new cases, and they start to decrease. So far, the state with the highest vaccination rate has been Mato Grosso do Sul, with 3.3% of people immunized with both doses.
Tocantins is the state where more people (83%) need to be vaccinated to change the course of the pandemic. This is because it is the place with the most uncontrolled progression of cases. When the survey was conducted, between February 22 and March 22, the reproduction rate was 1.72. This means that 100 infected people passed the disease to 172 others.
– Social isolation measures are also effective in decreasing the rate of transmission, which decreases the number of people who need to be vaccinated for the pandemic to be under control. That is, so that the number of new ones falls daily – says researcher Beatriz Carniel, doctor in Tropical Medicine and a member of Ação Covid-19.
Of the 83% inhabitants who need to be vaccinated in Tocantins, only 2.16% have already been immunized. São Paulo, in turn, would need 46.98% of the vaccinated population, but of that total, it only applied doses in 5.62%.
The study’s researchers argue that the distribution of doses should be done by the urgency criterion – and not proportionally to the population of the priority group, as is currently done. According to Carniel, this is a matter of equity.
– What appears in this study is the need for a different distribution of vaccines, from state to state, at every moment of the pandemic – says the expert, who concludes: – Considering the shortage of vaccines, it would be necessary to prioritize states with greater need for control transmission of the virus and focus on immunization distribution efforts.
Rio de Janeiro and Maranhão are the states where, currently, fewer people (22%) need to be vaccinated to reach the point where the pandemic is under control.
However, this does not mean that people do not need to be vaccinated after this level, the researchers explain, nor that life would return to normal. This can only happen when the states achieve herd immunity – which, in theory, means at least 70% of the immunized population.
Carniel signs the study with Pamela M. Chiroque-Solano (UFR), José Paulo Guedes Pinto (UFABC) and Patrícia Magalhães (University of Bristol UK), all members of Ação Covid-19. Created in May 2020, the interdisciplinary research group brings together scientists and researchers from different fields of knowledge to study the development of the pandemic in Brazil.
In December, when the level of contamination was lower than it is now, no state in the country would have to vaccinate more than half of the population for cases to fall, according to the criteria adopted by the Covid-19 Action study.
Maranhão, for example, would only need to immunize 13% of the population. In the period between February 22 and March 22, the index rose to 22%.
– After December, we see a scenario that would require an unattainable effort to control the pandemic, given the current availability of vaccines in Brazil – says Pamela Chiroque, PhD in Statistics and also a member of Ação Covid-19.
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