Explaining the cases of 'immortality' in the world of COVID-19.

More than two years after Covid-19 emerged, most Americans have developed immunity against the virus—thanks to vaccines, previous infections, or a combination of both. But there are rare cases where some unvaccinated individuals appear to avoid the virus despite multiple exposures.

This has raised the question of whether those individuals have natural immunity against Covid-19.

Scientists are trying to understand whether this ability exists and how it works. Studying these cases could help develop new vaccines and treatments against Covid-19.

Professor Shane Crotty, a virologist at the La Jolla Institute for Immunology (USA), said one possibility is that those who have not been infectedCovid-19They were lucky. That could also be due to their actions, such as wearing masks correctly or avoiding situations that could easily put them at risk of infection.

Conducting screening examinations for children before administering the Covid-19 vaccine. Photo: 자료 (Source: archive)

Catherine Troisi, an infectious disease epidemiologist at the University of Texas School of Public Health, commented: "I think a more plausible explanation is that some people have been infected with Covid-19 but are asymptomatic. Therefore, they don't know they have the disease."

Scientifically, according to Professor Crotty, there are two explanations for why some people have much higher resistance to the SARS-CoV-2 virus than others. First, this group may be able to eliminate the virus quickly, before it reaches detectable levels, due to immunity to other coronaviruses such as the common cold.

There are over 200 types of common cold viruses – four of which are coronaviruses, accounting for about 30% of all common cold cases. According to the U.S. Centers for Disease Control and Prevention (CDC), most people will contract one or more seasonal coronaviruses at some point in their lives.

Antibodies, acquired from vaccines or previous infections, attack newly invading viruses. Meanwhile, T cells prevent the virus from multiplying and causing severe disease. T cells appear to be effective against different types of coronaviruses, exhibiting a cross-reactivity.

Using extracorporeal membrane oxygenation (ECMO) – an artificial heart-lung machine – saves the lives of patients recovering from Covid-19. Photo: Tat Ngoc

A study of healthcare workers in the UK, published in November 2021, yielded similar results. The analysis examined individuals who had been exposed to the virus but did not test positive for SARS-CoV-2. The presence of T cells contributed to the rapid clearance of SARS-CoV-2 and the diseases caused by coronaviruses.

Another explanation is that some people have innate immunity to genetic factors that protect them from SARS-CoV-2 infection.

Associate Professor Neville Sanjana of New York University has studied the underlying genetic factors that contribute to Covid-19 resistance. To enter the human body, the SARS-CoV-2 virus needs to bind to the ACE2 receptor. Mutations in ACE2 may make it more difficult for the virus to do so.

A similar case has been demonstrated in AIDS. “With HIV, the virus that causes AIDS, the receptor that enters the body is CCR5. Some people have mutations that remove CCR5 and they are virtually immune to HIV,” said Associate Professor Sanjana.

Scientists also examined other genetic variations in the human genome.

"Humans have about 20,000 genes, and we really don't know which genes might affect the cells in the airway epithelium or in the lungs – the entry point for SARS-CoV-2," Associate Professor Sanjana shared.