Manaus shows that natural infection does not generate protection and cannot be an option for the world

The threshold for herd immunity is not a fixed value. It is calculated based on the contagion rate. To calculate the threshold of herd immunity, it is necessary to know the Rt and this value is an estimate

In Manaus, hospitals are still full, the waiting list for admission to the public network is stil high, deaths by COVID-19 continue to happen by the dozens and the flexibilities added to the new and evident relaxation of the population in relation to distance measures, can lead to unpredictable consequences due to a new upsurge in the second wave of contagion and mortality from the new coronavirus.

In August 2020, when Manaus recorded three months of sharp decline in cases of COVID-19 even after reopening schools and commerce, Brazilian experts raised the hypothesis that the threshold of collective immunity to the virus would have been reached, even though, the serological surveys pointed to less than 30% seroprevalence in the entire North region. The idea gained strength in September, when researchers from the University of São Paulo (USP) and collaborators published the article entitled “COVID-1910.1101/2020.09.16.20194787 herd immunity in the Brazilian Amazon”, using blood bank samples, which estimated by mathematical modeling that seroprevalence in the capital of Amazonas would be 66%, that is, it would be close to the threshold calculated at the beginning of the pandemic by the classic formula used in epidemiology.

In December, when the final version of the study was released, entitled “Three-quarters attack rate of SARS-CoV-2 in the Brazilian Amazon during a largely unmitigated epidemic”, also coordinated by the professor of the Department of Infectious Diseases at the USP School of Medicine and director of the USP Institute of Tropical Medicine, Dra. Ester Sabino, the estimate was that 76% of manauaras [residents of Manaus] already had immunity against the new coronavirus.

Could it be that the loss of immunity caused the second wave of infections in Manaus? Dr. Sabino, one of the most renowned Brazilian immunologists, who participated in the sequencing of the genome of the new coronavirus, explains that the work carried out showed what the attack of the infection was in Manaus. “According to our measurements, the percentage was 76% in October. We did several other analyzes with ours and other data and we always ended up reaching values very close to this. This data has a value that is theoretical for herd immunity, which is 66%. Therefore, our data is above the theoretical value of a herd immunity”, she points out.

Still according to the researcher, a natural herd immunity only works if there is no reinfection. In her his assessment, the epidemic in Manaus, can only be explained by loss of immunity associated with a variant that can stand out from this initial immunity to infection and this happens very often. Reinfection is common among the other coronaviruses and there would be no reason to think that the same would not happen with Sars-CoV-2”, argues Dr. Sabino

To have an idea, between the first and second outbreaks of COVID-19, a report published by G1, shows that the month of April 2020 registered 2,128 new admissions, a number that was surpassed between January 1st and 12th , with 2,221 new admissions. On May 29 the moving average of new cases per day was 1,696. On January 14 that number peaked with 2,080 cases a day. The state registered 3,816 new cases on January 14, 2,516 of which in Manaus alone. It was the highest number recorded in the state and in the capital of Amazonas since the beginning of the pandemic, in March 2020.

According to figures released by the Ministry of Health on February 2nd, the coronavirus killed 2 thousand people per million inhabitants in Amazonas. The rate is higher than that registered in Belgium, the country where COVID-19 kills the most in relation to the size of the population. In the European country, up to the beginning of February, 1,818 victims per million were counted.

In the evaluation of Dr. Sabino, the size of the epidemic in Manaus is associated with a strain with a higher rate of transmissibility and probably with a higher rate of pathogenicity “We are trying to measure and define the pathogenicity rate of this new strain, this has not yet been defined because it is not something as simple to do”, says the immunologist who sequenced the genome of the new coronavirus.

Entitled Resurgence of COVID-19 in Manaus, Brazil, despite high seroprevalence, an article published in The scientific journal The Lancet, on January 27, recalls the study which showed that 76% of the population of Manaus had antibodies against the new coronavirus. With this, the capital of Amazonas would have achieved herd immunity, estimated to be between 60% and 70%. The new work presents four non-exclusive hypotheses for the COVID-19 epidemic that started again in December in Manaus. In addition to the loss of contaminated immunity, the article mentions the possibility that herd immunity has not been achieved, that Sars-CoV-2 mutations circumvent the immune protection created by previous infections and that new virus variants have a higher transmission rate. The research, also led by Dr. Ester Sabino, brings together 23 other researchers, and is based on the number of cases, hospitalizations and deaths due to COVID-19 to analyze the transmissibility characteristics of the strains of the new coronavirus in circulation in the capital of Amazonas.

Apparently, the P.1 variant is not the only one that Amazonas should be concerned about, since there are other equally dangerous variants circulating in Brazil and it is not yet known what their effect is on the same region. While the virus continues to claim lives around the world and in Brazil, errors with vaccination continue in full swing with the country surpassing the 280 thousand confirmed deaths by COVID-19, without considering the underreporting and indirect deaths caused by the pandemic.