Six months after acquiring SARS-CoV-2, the blood of individuals who had mild, moderate, or asymptomatic COVID-19 still contained immune cells that recognize the virus, a new study finds.
The new research suggests that people reacquiring the infection may be rare because helper T cells, a type of immune cell, continue to protect most people against the virus for at least 6 months.
Between March and April 2020, 100 individuals who had recently recovered from COVID-19 agreed to participate in the study. Their symptoms had been mild or moderate, or they were asymptomatic, with none requiring hospital treatment.
The oldest participant was 65 years and the youngest was 22 years, while 77 were female.
They gave blood samples once a month, which allowed the researchers to track changes in antibody levels targeted at three different viral proteins.
After 6 months, all the participants had helper T cells remaining in their blood that responded to the virus. One of the key ways the cells responded was by producing IL-2, an immune-signaling molecule that is particularly important for combating viral infections.
Compared with individuals who experienced no symptoms, the T cell responses of those who had symptoms were 50% stronger.