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Why Do Some People Get Covid When Others Don’t?

An increasing amount of research is being devoted to indetify the reasons why some people never seem to get Covid. 

Last month, a new research was published by Imperial College London, suggesting that people with higher levels of T cells (a type of cell in the immune system) from common cold coronaviruses, were less likely to become infected with SARS-CoV-2, the virus that causes Covid-19.

Dr. Rhia Kundu, first author of the study from Imperial’s National Heart and Lung Institute, said that “being exposed to the SARS-CoV-2 virus doesn’t always result in infection, and we’ve been keen to understand why.”

Why Do Some People Get Covid When Others Don’t?

“We found out that high levels of pre-existing T cells, created by the body when infected with other human coronaviruses like the common cold, can protect against Covid-19 infection,” she said.

However Kundu also mentioned that, “while this is an important discovery, it is only one form of protection, and I would point out that no one should rely on this alone. Instead, the best way to protect yourself against Covid-19 is to be fully vaccinated, including getting your booster dose.”

Omicron Covid immunity doesn’t appear to be that durable, says Dr. Scott Gottlieb Lawrence Young, a professor of molecular oncology at Warwick University, told CNBC on Wednesday that, “there’s much interest in these cases called ‘never Covid’ – individuals who have clearly been exposed to close contacts in their household who are infected, but they are resistant to infection.”

He said that early data suggests that these individuals have naturally acquired immunity from previous infections with common cold coronaviruses.

Around 20% of common cold infections are due to common cold coronaviruses, he said, “but why some individuals maintain levels of cross-reactive immunity remains unknown.”

As well as a degree of immunity provided by prior exposure to coronaviruses — a large family of viruses that cause illness ranging from the common cold to more severe diseases or infection — one’s Covid vaccination status is also likely to be a factor as to whether some people are more susceptible to Covid than others.

Covid vaccination is now widespread in most Western countries, albeit with variations among populaces in terms of which coronavirus vaccine was administered, and when.

Booster shots are also being deployed widely, and younger children are being vaccinated in many countries, as governments race to protect as many people as possible from the more transmissible, but less clinically severe, omicron variant.

Covid vaccines have been proven to reduce severe infections, hospitalizations and deaths, and remain largely effective against known variants of the virus.

However, they are not 100% effective in preventing infection and the immunity they provide wanes over time, and has been somewhat compromised by the omicron variant.

Andrew Freedman, an academic in infectious diseases at Cardiff University Medical School, told CNBC that why some people get Covid and others don’t “is a well recognized phenomenon and presumably relates to immunity from vaccination, previous infection or both.”

Another question that has arisen during the pandemic is why two people with Covid may respond so differently to the infection; one could have heavy symptoms, for instance, and the other could be asymptomatic.

The answer might lie in our genes.

“It’s a really important question,” Imperial College’s Altmann told CNBC.

He said that he and his colleagues have conducted research, to be published soon, into immunogenetics (essentially, the relationship between genetics and the immune system) and Covid-19 infection, and have found that variations between people’s immune systems “makes a difference, at least to whether or not you get symptomatic disease.”

The research is focused on different HLA (human leukocyte antigen) genes and is looking at how these can affect one’s response to Covid, with some HLA types more or less likely to experience a symptomatic, or asymptomatic, infection, he said.

“The key genes that control your immune response are called HLA genes. They matter for determining your response on encounter with SARS-CoV-2. For example, people with the gene HLA-DRB1*1302 are significantly more likely to have symptomatic infection,” Altmann added.

The professor also pointed to the first results released Wednesday of a British human challenge trial, carried out by Imperial and several other research bodies, in which 36 healthy young adults were deliberately exposed to Covid, but only half of them actually became infected with the virus.

“How is it that you pipette an identical dose of virus into people’s nostrils and 50% become infected, the other 50% not?,” Altmann asked, referring to the method used in the trial to expose the participants to the virus.

Essentially all the trial volunteers were given a low dose of the virus — introduced via drops up the nose — and then carefully monitored by clinical staff in a controlled environment over a two-week period.

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