About one-fifth of people infected with covid-19 were completely asymptomatic. Patients who showed no symptoms were likely to carry a genetic mutation called HLA-B. In a study performed with 1400 people who carry this gene and tested positive for covid-19, 136 of them reported no symptoms. Roughly 20 percent of these asymptomatic patients carried at least one copy of the HLA-B gene. And if a patient carried two copies of the gene, they were reported to be eight times less likely to report any symptoms after testing positive. Upon examination of patients with this gene, it was discovered that they contained T cells that reacted to the proteins found in the Covid-19 virus. Which likely gave them an increased immunity to the virus which explains why they never showed any symptoms.
The implications of this discovery could be incredibly profound for future vaccines. If researchers are able to perfect how the HLA gene acknowledges proteins, they could potentially make more effective vaccines for future viruses.