Two studies recently released on the platform medRxiv, still without peer review, show how the delay in vaccination against COVID-19 in Brazil can compromise the efficiency of the campaign in terms of reducing the number of deaths from the disease at the current epidemic peak.
In one of articles, whose main author is a professor at the Faculty of Medicine of the University of São Paulo (FM-USP) Eduardo Massad, it is estimated that about 127 thousand lives would be saved by the end of 2021 if Brazil had started on January 21 to vaccinate en masse – something around 2 million doses applied per day. The current average has been 2,000 people immunized daily, that is, 10% of what is considered ideal by researchers based on the potential shown by the Unified Health System (SUS) in previous campaigns.
If the immunization efforts had taken shape a month later, on February 21, the number of deaths prevented would have dropped to 86,400 by the end of the year. As time goes by the estimate decreases to 54,500 (March 21), 30,300 (April 21) and 16,400 (May 21).
“Apparently, mass vaccination in Brazil should only really start in August. And that is if Instituto Butantan and Fiocruz fulfill their promise to deliver 150 million doses by July. Nor am I counting on vaccines from other laboratories, such as Pfizer, Moderna or Janssen, because if they arrive in the country in the first semester it will be the dropper. For a different scenario to be possible, this negotiation should have been done last year ”, says Massad in an interview with FAPESP Agency.
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By means of mathematical modeling and based on the trends observed in December 2020 (transmission rate and daily number of new cases – without considering the new Brazilian variant), the group led by the professor at FM-USP calculated that, if no effort to vaccination was carried out throughout 2021, the country would reach the end of the year counting 352,900 victims of COVID-19.
“This is an underestimate, because with the arrival of the new strains of SARS-CoV-2, the epidemic curve has become much more pronounced. This projection [de mortes até 31 de dezembro de 2021 em um cenário sem vacinação], in the current context, would probably exceed 400 thousand deaths. In other words, all the numbers presented in the article now become the minimum, the floor ”, assesses Massad.
For the researcher, Brazil is already experiencing the third wave of COVID-19, which would have started after the peak of cases observed in January this year. “The second wave did not even fall substantially when the new variant emerged [P.1.] and the number of cases has accelerated again. For four weeks now we have broken record after record ”, he says.
Considering the current context, Massad estimates that another 100 thousand Brazilians should die by the end of the year due to the delay in vaccination. If it were possible to anticipate the start of the mass immunization for May, that number would be reduced by approximately half.
“We must have between 30 and 40 million doses for the first semester and that is not enough to meet even half of the group considered at risk, which covers 77 million people. With 40 million doses, we will only vaccinate 20 million individuals in that period, that is, less than a third of what is necessary ”, points out the researcher.
In Massad’s assessment, therefore, the impact of vaccination in the course of the epidemic will be practically zero in the first half of 2021. “If the cases start to fall, it will certainly be due to the natural course of the disease or the measures of social isolation, which are increasingly difficult to implement. ”
All estimates described in the study were made considering a vaccine with 90% effectiveness, higher than the number of immunizers already available in Brazil (Covidshield, from AstraZeneca / Fiocruz and CoronaVac, from Sinovac Biotech / Instituto Butantan). However, Massad says that all immunizers already approved for emergency or permanent use have been shown to be equally effective in preventing deaths from COVID-19, which is the main parameter evaluated in the research.
Speed ??makes a difference
The second study on the topic was conducted by Thomas Vilches, postdoctoral at the Institute of Mathematics, Statistics and Scientific Computing at the State University of Campinas (Unicamp), and had the collaboration of researchers from the State University of São Paulo (Unesp) in Botucatu.
Also by mathematical modeling, the group designed 18 scenarios related to the impact of the vaccination campaign on the number of admissions and deaths due to COVID-19 in São Paulo at the current epidemic peak.
Among the factors that change in the different scenarios are: the vaccine used (CoronaVac or Covidshield), the speed in the distribution of doses (630 thousand or 1.2 million per day throughout the country), the protection of each immunizer against severe symptoms (which varied between 0% and 100%), the protection of vaccines against infection (which also varied from 0% to 100%) and the degree of risk perception of each individual vaccinated, that is, how much he respects the measures isolation.
When adjusting the model, the researchers considered that around 20% of the population in São Paulo had already been infected and had antibodies against SARS-CoV-2. In addition, a virus transmission rate of 1.04 was considered (each 100 symptomatic infected individuals generate another 104 symptomatic). This was the amount reported to São Paulo in January by COVID-19 BR Observatory.
“In the scenario that we call basal [baseline], we consider that 0.3% of the population of the country would be vaccinated daily and this gives something around 630 thousand doses a day. This speed of distribution would be possible to be achieved only with the doses provided by the Butantan Institute, when the production reaches the ‘cruising speed’ [1 milhão de doses ao dia]. In the scenario that we call ‘double speed’, 0.6% of the population would be vaccinated per day, which could be done by adding the doses produced by Butantan and Fiocruz ”, says Vilches.
The researcher points out, however, that even the scenario considered baseline in the study is faster than the pace currently recorded across the country. “Brazil has a great capacity to distribute doses, thanks to the SUS structure. Our problem is production, ”he says.
The projections indicate that with CoronaVac, in the best scenario – that is, considering 100% relative protection (which is to say that protection against infection is 50.3%, equivalent to the overall effectiveness) and 100% of protection against severe symptoms -, it would be possible, at baseline speed of distribution, to reduce by 45.3% the number of deaths due to COVID-19 in the current epidemic peak. With Covidshield, also in the best scenario, the reduction would be 57%.
If the speed in the distribution of doses was doubled, the percentages (referring to the reduction of deaths) would jump to 65.7% with CoronaVac and 74% with Covidshield.
“With double the speed, even in the worst scenario [aquele em que a vacina oferece 0% de proteção contra sintomas severos e 0% contra infecção], CoronaVac could reduce the number of deaths by 30% and Covidshield by 46.8% ”, estimates Vilches.
According to the researcher, the main message of the work is that, for the campaign to have a significant impact on the reduction of deaths, every possible effort must be made to accelerate the pace of vaccination in the country, including the purchase of immunizers from other laboratories. “The more vaccines are purchased, the better. There is no justification for not doing so. Vaccinating quickly is essential to prevent deaths and also to stop the emergence of new strains that are even more aggressive ”, he says.
The study Vaccination efforts in Brazil: scenarios and perspectives under a mathematical modeling approach, by Thomas Nogueira Vilches, Felipe Alves Rubio, Rafael Augusto Forti Perroni, Gabriel Berg de Almeida, Carlos Magno Castelo Branco Fortaleza and Cláudia Pio Ferreira, can be read at www.medrxiv.org/content/10.1101/2021.02.22.21252208v1.full.pdf.
The article Modelling the Impact of Delaying Vaccination Against SARS-CoV-2 Assuming Unlimited Vaccines Supply, by Marcos Amaku, Dimas Tadeu Covas, Francisco Antonio Bezerra Coutinho, Raymundo Soares Azevedo and Eduardo Massad, is available at www.medrxiv.org/content/10.1101/2021.02.22.21252189v1.full.pdf.