Phoebe Garrett attended university lectures without being infected with Covid-19. She even threw a party where everyone tested positive, except her.
“I think I was exposed on purpose about four times”the 22-year-old from High Wycombe, a large town in Buckinghamshire, England.
In March 2021, she participated in the world’s first Covid-19 challenge trial. The test involved instilling a live virus into her nose and sealing her nostrils for several hours, in a deliberate attempt to infect her. But her body still resisted it.
“We had many rounds of testing and different testing methods: put a cotton swab in the throat, pick the nose, put the swab in the nose for one minute,” he said. Garrett said. “My mother always said that our family never got the flu, and I wondered if there was something behind it.”
Phoebe Garrett, who participated in the world’s first Covid-19 challenge trial, but did not develop symptoms or test positive.
Most people know someone who didn’t test positive for Covid-19, despite everyone around them falling ill. Exactly how they did this is still a mystery, but scientists are starting to find some clues.
And this research offers hope that identifying these mechanisms could lead to the development of drugs that not only protect people from catching Covid-19, but also prevent them from transmitting it.
Garrett isn’t the only one to take the challenge uninfected. Of the 34 people exposed to the virus, 16 were not contagious (defined as two consecutive positive PCR tests) – although about half of them tested positive for the virus. low withdrawal, usually several days after exposure.
“Possibly, this is a reflection of how quickly the immune system is able to suppress infection from infancy.”said Professor Christopher Chiu at Imperial College London, who led the study.
“In our previous studies with other viruses, we have seen early nasal immune responses that are associated with fighting infection.”he said. “Taken together, these findings imply that there is a struggle between the virus and the host, in participants who are not infected, leading to preventing infection from taking place.”
Some of these people also reported mild symptoms, such as a stuffy nose, sore throat, fatigue, or headache. Even so, since these symptoms often occur in everyday life, they may not be related to exposure to the virus.
Mr. Chiu said: “Either way, levels of the virus don’t rise high enough to trigger detectable levels of antibodies, T-cells or inflammatory factors in the blood that are commonly associated with symptoms.”
Electron microscope image of Sars-CoV-2 virus.
Other studies have also shown it is possible to clear Covid-19 in the earliest stages of infection, before it has established a proper foothold in the body. For example, during the first wave of the pandemic, Dr Leo Swadling at University College London and colleagues closely monitored a group of healthcare workers who had frequent contact with infected patients, but never tested them. test positive or develop autoantibodies. Blood tests showed that about 15% of them had T cells that responded to Sars-CoV-2, plus other signs of viral infection.
It is possible that memory T cells from previous coronavirus infections – i.e. those that cause the common cold – cross-reacted to the new coronavirus and protected them from Covid-19.
Understanding how often people passed Covid-19 infections early in the age of the widespread Omicron variant was complicated, as it required intensive testing – for viruses, antibodies, T cells. and other signs of infection – and because so many people have been vaccinated.
“It’s possible that vaccinated people were exposed to the virus and prevented the virus from replicating or spreading,” he said. Swadling said.
Nor is there currently any commercial test that can distinguish between immunity triggered by vaccination and different variants. So unless a person has recently tested positive, it is virtually impossible to know if they have been exposed to the Omicron variant.
Seasonal coronaviruses may not be the only source of cross-protective immune responses. Professor Cecilia Söderberg-Nauclér, an immunologist at the Karolinska Institutet in Stockholm, began investigating this possibility, after Sweden avoided being hit hard by cases during the first wave of the pandemic. Mathematical modeling by her colleague, Marcus Carlsson at Lund University, suggests that this infection pattern can only be explained if large numbers of people have some sort of protective immunity.
Her team searched databases of protein sequences from existing viruses, looking for small segments (peptides) that resemble those from the new coronavirus, to which antibodies are likely to bind. When they identified a six-amino acid peptide in an H1N1 flu protein that matched a key part of the coronavirus spike protein, “I almost fell out of my chair”says Söderberg-Nauclér.
Since then, they have detected antibodies to the peptide in 68% of blood donors from the capital, Stockholm. Research has not yet been reviewed, which may suggest that immune responses caused by H1N1 flu – which caused the 2009-2010 swine flu pandemic – and possibly related to subsequent strains, may may have partially, though incompletely, equipped humans with protection against Covid-19. Söderberg-Naucler says: “It provides a cushion, but it won’t protect you if an infected person coughs in your face.”
A small number of people may even be genetically resistant to Covid-19. In October, an international team of researchers launched a global hunt to find these people, in the hope of identifying protective genes.
Professor András Spaan at Rockefeller University in New York, who led the program, said: “We are not looking for common gene variants that offer modest protection against infection, what we are looking for are very rare gene variants that are able to fully protect a person against infection. re-infection.”
They are particularly concerned about people who live in the same house and sleep in the same bed as someone who is infected but does not infect themselves. “For example, the other day I was talking to an elderly woman from the Netherlands who took care of her husband for the first time. The husband was eventually admitted to the ICU, but she had spent the previous week taking care of him, in the same room, and was not wearing a mask.” Spaan said. “We can’t explain why she wasn’t infected.”
Such resistance is known to exist for other diseases, including HIV, malaria and norovirus. In these cases, the genetic defect means that some people lack the receptors used by the pathogen to enter cells, so they cannot become infected. Spaan says: “It is possible that in some individuals, there is such a defect in a receptor used by Sars-CoV-2.”
The identification of such genes could lead to the development of new treatments for Covid-19, in the same way that identification of CCR5 receptor defects in HIV-resistant individuals has led to HIV treatments. new.
Spaan said it is unlikely that the majority of people who have avoided Covid-19 are genetically resistant to the disease, even if they have some measure of immune protection. This means there’s no guarantee they won’t eventually get infected – as was the case with Garrett who was found to be infected at the end of January. After avoiding the virus for almost two years, she was shocked when the quick test results showed a worrying second red line. A short time later, she developed mild Covid-19 symptoms, but later recovered.
The irony is that, having avoided being infected with Covid-19 from family, close friends and even in a specialized medical laboratory, it was possible that an unfamiliar relative infected her. “I don’t know where I got it from. It could be someone from the local choir, or it could be from the gym.” she said.
Refer TheGuardian