The world’s first experiment has revealed why some people never catch the coronavirus. A detailed comparison of COVID-19 cases has shed light on why not everyone falls victim to the severe illness that brought much of the world to its knees.
Through an analysis of genetic activity in the nasal and blood tissues of individuals with “failed” SARS-CoV-2 infections, a research team led by the Wellcome Sanger Institute and University College London (UK) discovered a new immune response that provides robust protection for the body.
While vaccines significantly reduced the risk of death and severe complications from COVID-19, they did not always prevent the virus from establishing itself in the nasal mucosa and respiratory system.
For most people, a COVID-19 diagnosis meant weeks of suffering, accompanied by a runny nose, cough, and body aches. However, for a fortunate few, the infection was so fleeting that their bodies barely had time to produce even a single sneeze. This small cohort of individuals remained completely free of COVID.
Why are some people better protected than others? Until now, scientists struggled to answer this question, as field studies were complicated by the challenges of accurately determining the moment of infection.
How the Study Was Conducted
To overcome this obstacle, researchers conducted what is known as a controlled trial, according to Science Alert. They intentionally infected 36 healthy volunteers aged 18 to 30 with the pre-alpha strain of SARS-CoV-2 in a laboratory setting. Notably, 16 participants in the group had never been vaccinated and showed no signs of prior SARS-CoV-2 infection.
“This was an incredibly unique opportunity to observe immune responses in adults who had never previously been infected with COVID-19, under conditions where factors like the timing of infection and underlying health conditions could be controlled,” said biologist Rick Lindeboom.
Blood samples and nasal swabs taken from the volunteers over the year following infection were analyzed using single-cell RNA sequencing. As a result, the team obtained a temporal scale of activity for hundreds of thousands of individual cells with unprecedented detail.
Based on this dataset, the team identified three categories of infections: transient, persistent, and abortive. It was within this third group that they discovered the body’s secret weapon for avoiding the coronavirus.
While most people exhibit a rapid immune response against the virus that enters the bloodstream, the participants in the experiment showed a barely noticeable but much faster reaction in the nasal tissues. This included the activation of mucosal-associated invariant T cells (MAIT) and a reduction in inflammatory leukocytes. This helped eliminate the virus before it could take hold in the body.
The researchers also found increased expression of the HLA-DQA2 gene in the nasal cells prior to inoculation—one of several genes previously linked to mild or asymptomatic SARS-CoV-2 infections.
“These results shed new light on critical early events that allow the virus to establish itself or be rapidly cleared before symptoms develop,” noted senior study author Marco Nikolic.
“Now we have a much better understanding of the full spectrum of immune responses, which could serve as the foundation for developing potential treatments and vaccines that mimic these natural protective responses,” he added.
Understanding how human biology copes with viral attacks is vital. After all, we want to combat not only the coronavirus but also even deadlier diseases that we will undoubtedly face in the future. The study’s findings were published in the journal Nature.