Retired couple Maria do Carmo, 56, and Carlos Teixeira, 64*, who live in São Paulo, are an example of one of the greatest enigmas of the coronavirus pandemic. coronavirus. Why do some people get Covid-19 and others don’t?
already in time variant top micron – considered more transmissible, they traveled with two friends. A few days later, one of them called saying, “We’ve been infected.”
“We traveled by car, slept in the same room, barbecued. When they alerted us, we went to do the testsays Mary. Hers was positive, her husband’s was negative. Maria and Carlos fell asleep separately, trying to avoid contact, but it didn’t seem necessary. He didn’t even sneeze.
Since the start of the pandemic, scientists have sought to understand cases like this, which have become a common topic in conversation circles.
Biologist and geneticist Mayana Zatz directs transmission studies of SARS-CoV-2 to University of Sao Paulo (USP). One of the group’s main conclusions is a possible genetic explanation for the situation.
The researchers looked for discordant couples (when one catches the virus but does not pass it on to the other) and sequenced some of the DNA volunteers.
“We realized that there was a difference in certain genes responsible for immune response and that infected people with symptoms have a delayed response of NK cells called natural killerswhich constitute the first barrier of defense of our body against infections”, explains Mayana.
In those who do not fall ill, the reverse happens, these cells seem to be faster, destroying the virus without giving it a chance to replicate or spread.
Genetic research goes beyond couples. “We have evaluated centenarians who are immune to the Spanish flu and, now, to the coronavirus”, reveals the biologist.
All these analyses, still in progress, aim to identify the lineages of carriers protective genes and more answers on our interaction with the virus. “These data could lead to future covid-19 treatments and also prepare us more for the next pandemics, ”assesses Zatz.
Infected at different times
Genetics may explain who defends itself best from the virus, but transmission has remained like a lottery in the home of journalist and publicist Paula Novaes, 26. She, her boyfriend, stepmother, and stepfather live together, and each caught the disease at different times.
“It started with my stepfather at the start of the pandemic. He works in a market. The office is closed, but lunch is in the cafeteria, there was no way to avoid it,” says Paula.
Even at 65, an age already considered at risk, Luiz Duarte only had symptoms similar to those of a influenza strong. After the positive test, his wife, lawyer Cléa Duarte, 68, went to sleep elsewhere, sorted the cutlery and everything else.
At that time, nothing happened. But at the end of last year, Cléa was infected. “We were watching TV in the bedroom with another person. My mother-in-law was already sneezing. When he started having more symptoms he decided to take the test and he was positive. The other person who was in the room also took it, but I am once again unscathed”, says the journalist.
Paula’s boyfriend, investment adviser Tarcísio Duarte, 31, fell ill months later. “He started to weaken, with aches, but I was dieting and running, training a lot. We treated the pain in the body with ice, we continued to sleep together, until shortness of breath came,” she reports.
After four days of symptoms and another three awaiting the test result, he found out he had Covid. “It was only then that I isolated myself and took the test, which came back negative,” she says.
Paula already felt immune to the coronavirus until his turn – and it was in the season of Ômicron. “I felt fever and cough, I felt bad at work, I took the test and it was negative. I did not progress, I insisted on the test, and this time it was positive. At that time, home transmission took place and the boyfriend was infected again.
Everyone was fine in the end, but no one understood exactly what had happened.
Naturally resistant and transmission window
The virologist Paulo Eduardo Brandão, Columnist VEJA SAÚDE and professor at USP, recalls that any infectious disease will have a naturally resistant group of people and certain factors are necessary for the virus to pass from one host to another.
“Transmission depends on the contact time between two people and the state of immunity of both,” explains the professor from the University of São Paulo.
There is still the transmission window. Once the virus enters an individual’s body, it takes time for it to lodge and begin to replicate. hence the importance of testing yourself on good days.
Tests are usually done when symptoms are more present, so the the viral load is high. That is, it is much easier for transmission to occur at this time. This can happen even when the infected person is asymptomatic.
Still in relation to contagion, another point raised by these latest studies is that men transmit more than women.
To make this observation, tests were carried out to detect the SARS-CoV-2 by saliva, which detected that boys have a virus load in the liquid about ten times higher than that of women, in particular up to 48 years of age.
And the variants?
Throughout the pandemic, a lot has happened, between changes in behavior and the emergence of variants. “We recontact these same couples to see if those who have not fallen ill remained resistant to Omicron“, reports the biologist and researcher at the USP. Other variables will be assessed at this stage, such as whether these couples are now vaccinated.
Norwegian scientists have already made a study last with the mutants, published in the academic journal never. They looked for people with positive Covid tests who shared the house with more people. Out of 31,220 cases of transmission in the same house, 25% of them occurred with the Ômicron variantand others 19% with Delta.