Faces-neverCOVID: why some people never become infected with coronavirus, despite contact with sick people

The greatest mystery has arisen as a result of the COVID-19 pandemic. Infectious disease experts are puzzled over why some people get coronavirus infection and others don't, even if they're equally exposed to the virus. CNBC.

Many of us know entire families who have been infected Covid and have been forced to self-isolate due to the pandemic. However, there are also many stories of couples, families and colleagues, among whom some have contracted the virus, while others have not.

Danny Altmann, professor of immunology at Imperial College London, told CNBC that the chance of infection in a family after one positive case is "not as high as you might imagine," according to the study.

People who have never been sick COVID-19

A growing body of research is focusing on the reasons why some people never seem to be exposed to this infection.

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Last month, Imperial College London published a new study suggesting that people with higher levels of T cells (a type of cell in the immune system) are less likely to become infected with SARS-CoV-2, the virus that causes COVID-19.

Dr Ria Kundu, first author of the study at the Imperial National Heart and Lung Institute, said that "exposure to the SARS-CoV-2 virus does not always lead to infection, and it is very tempting to understand why."

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

However, Kundu warned that "although this is an important discovery, it is just one form of protection." But, she stressed, “no one should rely on this alone; The best way to protect yourself from COVID-19 is to complete a full vaccinationincluding revaccination.

Lawrence Young, professor of molecular oncology at the University of Warwick, stated that “there is a lot of interest in cases of so-called never sick COVID-19 people. They have clearly been subjected to close contact in their family with the infected, but they themselves are resistant to infection.”

He said early evidence suggests that these people have acquired natural immunity from previous cold coronavirus infections. About 20% of cold infections are caused by cold coronaviruses, he said, "but why some people maintain levels of cross-reactive immunity remains unknown."

In addition to the degree of immunity provided by previous exposure to coronaviruses (a large family of viruses that cause illnesses ranging from the common cold to more severe diseases or infections), COVID-19 vaccination status is also likely to be a factor in determining whether some people will be more susceptible to coronavirus infection than others.

The role of vaccines

Now vaccination against COVID-19 is widespread in most Western countries. But there are differences among the population about which coronavirus vaccine was given and when.

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Booster vaccinations are also widely used, and young children are being vaccinated in many countries. Thus, governments seek to protect as many people as possible from a more contagious, but less clinical variant. omicron.

COVID-19 vaccines reduce severe infections, hospitalizations and deaths. They remain largely effective against known variants of the virus. However, they are not 100% effective in preventing infection, and the immunity they provide weakens over time, and the omicron variant has somewhat compromised it.

Andrew Friedman, an infectious disease specialist at Cardiff University School of Medicine, told CNBC that the reason some people get COVID-19 and others don't is "a well-known phenomenon and presumably related to immunity from vaccination, previous infection or of both."

“We know that many people did get infected (mostly mildly) with the omicron variant even though they were fully vaccinated, including a booster. However, vaccination still reduces the chance of omicron infection, and reactions vary from person to person. So some people get infected and others don't, even though the exposure is very significant,” he said.

Young from the University of Warwick observed that when it comes to different immune responses to COVID-19, “certainly, cross-reactive immunity from previous cold coronavirus infections is likely to be a major factor, especially as these individuals may have additional immune benefits due to that they were also vaccinated."

Further research into so-called never-infected people will help better understand the immune response to SARS-CoV-2. In addition, we will be able to understand “what aspects of cross-reactive response are most important and how this information can be used to create universal vaccines that are resistant to variants.”

Genetic factor

Another question raised during the pandemic is why two people with COVID-19 might respond so differently to the infection. For example, one person has severe symptoms while another is likely to be asymptomatic.

The answer may lie in our genes.

“This is a really important question,” says Altmann of Imperial College CNBC.

He and his colleagues have done research on immunogenetics (essentially the relationship between genetics and the immune system) and COVID-19 infection. They found that differences between people's immune systems "make a difference, at least whether or not you get a symptomatic illness."

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The study is working with various HLA (human leukocyte antigen) genes and studying how they can affect a person's response to COVID-19, he said. However, some types of HLA are more or less likely to experience symptomatic or asymptomatic infection.

“The key genes that control your immune response are called the HLA genes. They are important in determining your response to exposure to SARS-CoV-2. For example, people with the HLA-DRB1*1302 gene are significantly more likely to have a symptomatic infection,” Altmann explained.

Maybe it's tests

The professor also pointed to the first results published on February 2 British human trialconducted by Imperial and several other research organizations. In the study, 36 healthy young people were deliberately injected with COVID-19, but only half of them actually contracted the virus.

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

Essentially, all of the volunteers in the trials were given a low dose of the virus via nasal drops. Clinical staff were then closely monitored for two weeks in a controlled environment.

Of the 18 infected volunteers, 16 developed mild to moderate cold symptoms, including congestion or runny nose, sneezing and sore throat.

The researchers said for the first time they were able to provide detailed data on the early phase of the infection, before and during the onset of symptoms. Among the 18 infected participants, the median time from first exposure to the virus to the detection of the virus and the onset of the first symptoms (i.e., the incubation period) was 42 hours. This is significantly shorter than current estimates, which put the average incubation period at five to six days.

After this period, there was a dramatic increase in the amount of virus (viral load) found in swabs taken from the participants' noses or throats. These levels peaked on average about five days after infection. But high levels of viable (infectious) virus were still detectable in lab tests up to an average of nine days after vaccination, and for some up to 12 days.

More viruses in the nose

It is also interesting where the most viruses were found. While the virus was detected first in the throat and much earlier than in the nose (40 hours in the throat compared to 58 hours in the nose), virus levels were lower and peaked earlier in the throat. Peak levels of the virus were significantly higher in the nose than in the throat, indicating a potentially greater risk of virus shedding from the nose than from the mouth.

They noted that there is a possibility of "missing an infectious virus in the early stages of an infection, especially if only the nose is being tested." The researchers said the findings generally support the continued use of lateral flow tests to identify people who may be contagious.

“We found that, in general, immunochromatographic tests correlate very well with the presence of an infectious virus,” said Christopher Chiu, Professor of Infectious Diseases at the Institute of Infection at Imperial College London and principal expert on the study. sensitive, but if you use them correctly and repeatedly, and act on them if they are positive, it will have a big impact on stopping the spread of the virus.”