Strange Phenomenon During the Covid-19 Pandemic: Some Individuals Exposed to Positive Cases Remain Uninfected. Experts hope that studying these cases will aid in the development of drugs to prevent outbreaks.
Ms. Phoebe Garrett attended in-person classes at her university but did not contract Covid-19. She even hosted a party where all attendees tested positive afterward, except for her, according to the Guardian.
“I think I intentionally exposed myself to positive cases about four times,” said the 22-year-old from High Wycombe, England.
In March 2021, she participated in a world-first trial: scientists administered live SARS-CoV-2 virus into her nose and sealed it for several hours, in a deliberate attempt to infect her with Covid-19. However, her body successfully resisted the virus’s invasion.
Scientists are trying to unravel the mystery: Why are some people not infected with Covid-19?
Ms. Phoebe Garrett was exposed to many positive cases but did not contract Covid-19 – (Photo: THE OBSERVER)
Preventing Infection from the Start
Ms. Garrett is not the only participant in the trial. Among 34 individuals exposed to the SARS-CoV-2 virus, 16 remained uninfected. About half of them tested positive but with low viral loads, usually a few days after exposure.
This may reflect an immune system that quickly halts the infiltration of the infection from the outset. Professor Christopher Chiu at Imperial College London, who led the study, stated: “In previous studies with other viruses, we found that if SARS-CoV-2 is eliminated at the nasal mucosa, it is rendered incapable of causing disease.”
Other research also suggests that eliminating SARS-CoV-2 during its initial phase of entering the body, before it finds a suitable residence, is possible.
For instance, during the first wave of the pandemic, Dr. Leo Swadling at University College London and colleagues closely monitored a group of healthcare workers who frequently interacted with infected patients. They discovered that only about 15% of the staff had T cells reacting to the SARS-CoV-2 virus, along with other signs of viral infection.
It is possible that T cells from previous coronavirus infections—specifically those causing common colds—cross-reacted with the new coronavirus and protected them from Covid-19.
Seasonal Coronaviruses Provide a Buffer
Seasonal coronaviruses may not be the sole source of cross-protective immune responses.
Professor Cecilia Söderberg-Nauclér, an immunologist at the Karolinska Institute in Stockholm, began investigating this possibility after Sweden avoided a massive outbreak of Covid-19.
Her team searched databases for protein sequences from existing viruses. Upon identifying a 6-amino-acid peptide in a protein of the H1N1 flu virus that matched a crucial part of the coronavirus spike protein, she recalled, “I nearly fell off my chair.” Peptides are short chains of amino acids linked together.
Since then, they have discovered antibodies against this peptide in 68% of blood donors from Stockholm. The research suggests that immune responses triggered by H1N1—responsible for the 2009-2010 swine flu pandemic—may relate to subsequent virus strains. This response partially protects individuals, although not completely, against Covid-19.
Ms. Söderberg-Nauclér stated: “It provides a buffer, but it won’t protect you if an infected person coughs in your face.“
Genetic Resistance to Covid-19
A few individuals may even possess genetic resistance to Covid-19.
Last October, a group of international researchers launched a global hunt for individuals with this resistance gene, hoping to identify protective genes.
Professor András Spaan at Rockefeller University in New York mentioned: “We are searching for very rare gene variants that can completely protect a person from infection.”
They are particularly interested in those who live with and share a bed with infected individuals but remain uninfected.
“For example, one day, I spoke with an elderly woman from the Netherlands who cared for her husband, who was infected during the first wave, and she didn’t wear a mask. We cannot explain why she did not contract the virus.”
Such resistance is known to exist for other diseases, including HIV, malaria, and norovirus (common and highly contagious viruses that cause diarrhea and vomiting). In these cases, genetic defects mean some individuals lack receptors that pathogens use to invade cells, thus they cannot become infected.
Identifying such genes could lead to the development of new treatments for Covid-19, similar to how identifying CCR5 receptor defects in HIV-resistant individuals has led to new HIV treatment methods.
