The city of Brazil “may have reached herd immunity”

Manaus, the capital of the State of Amazonas, has recorded about 51,000 cases of COVID-19, killing more than 2,500 people from a population of less than 2 million.Many countries Not yet recorded 50,000 Case.

The herd immunity threshold (“basic epidemiological parameter”) is the percentage of the community that has acquired immunity to the disease through either vaccination or natural infection. The herd immunity threshold is reached when the number of people who can spread the disease is less than the proportion of people who have immunity.

Researchers led by a team at the University of São Paulo have no consensus as to what percentage of the population must be infected with COVID-19 before reaching herd immunity.

The theoretical herd immunity threshold for SARS-CoV-2, the virus that causes coronavirus disease, is about 60%, but some scientific models predict low values ​​of 20-43%. According to a preprint survey Published via medRxiv.

Global and regional decisions and the impact of vaccination campaigns to lift COVID-19 restrictions may be based on estimates of this threshold, they say.

The Amazon government has announced an attempt to contain the growing COVID-19 infection in the state. Tighter control measures September 24th, including the closure of bars and beaches.

Data suggest that the numbers declined slowly from May to September after a surge in cases in March and April. Physical restrictions and changes in population behavior “may have helped limit SARS-CoV-2 infection in Manaus, but unusually high infection rates help herd immunity determine the magnitude of the epidemic. It suggests that it played an important role, “the researchers say.

Studies show that Manaus can be used as a “sentinel” to determine the lifespan of herd immunity and the frequency of reinfection.

antibody

The team selected blood samples provided to two blood banks, São Paulo and Amazonas, between February and August to identify the antibodies.

“Blood samples are stored for six months, which allows direct measurement of the study,” said Esther Sabino, co-author of the study and professor of medicine at the University of São Paulo.Sabino Genome sequencing of novel coronavirus In Brazil at the beginning of the pandemic.

“If you are infected in March and donate blood in August, you do not have the same amount of SARS-CoV-2 antibody by then because the amount of SARS-CoV-2 antibody decreases over time. Therefore, the virus To calculate the actual prevalence of, we had to adjust the degradation rate, “she says. SciDev.Net..

“Our study found that there was no difference in the prevalence of COVID-19 between young and old donors, so we assumed it to be the same for the entire population.”

The Sabino team’s study used samples from blood banks, but the results were SoroEpi MSP A research project in which blood samples were collected from representative samples of the adult population (a series of solo epidemiological studies to monitor the prevalence of SARS-CoV-2 infection in the city of São Paulo).

SoroEpiMSP coordinator Celso Granato states that Sabino’s team’s assumption that the threshold for herd immunity was reached in Manaus is “very valid.” SciDev.Net..

“Theoretically, we believe that COVID-19 herd immunity accounts for about 60% of the virus-resistant population, so this study shows Manaus herd immunity,” said an infectious disease professor. Granato says. Federal University of São Paulo who did not participate in the study of Sabino.

These findings mean that the virus is less likely to find new victims in Manaus. However, Granato warns that “more than 30 percent of the population is still infected there.”

“The transmission may have been delayed in the state of Amazonas, but it’s still happening,” Sabino agrees.

Sabino’s research was supported by SciDev.Net donors FAPESP and Wellcome.

* About the author: Meghie Rodrigues is a science journalist and SciDev.Net Since 2017. Meghie is also a content researcher at the Museum of Tomorrow in Rio de Janeiro. She has also contributed to Ciência & Cultura magazine, Chemical & Engineering News and more.

Source: This work was produced by SciDev.Net’s Latin American and Caribbean desks.