During the pandemic, doctors and researchers found that children and young people infected with Covid-19 were less likely to get sick than adults.
Memory T cells generated by the common cold
Scientists estimate children already had previous immunity to Covid-19 provided by memory T cells generated by the common cold.
Researchers from Sweden’s Karolinska Institutet and the universities of Bern in Switzerland, Oslo in Norway and Linköping in Sweden examined blood samples from children taken before the pandemic and identified memory T cells that respond to cells that are infected with SARS-CoV -2, the causative virus, are infected with COVID-19. The study was based on 48 blood samples from children between the ages of two and six and 94 samples from adults between the ages of 26 and 83. Blood samples from 58 people who had recently recovered from Covid-19 were also analyzed.
A possible explanation for this immunity in the children is that they had caught a cold caused by one of the four coronaviruses that cause seasonal symptoms of the common cold. This could stimulate an immune response with T cells capable of responding to cells infected with SARS-CoV-2 as well.
The memory T-cell response to coronaviruses begins to develop from the age of two
The results also show that the memory T-cell response to coronaviruses is developing as early as two years of age. “These reactions are particularly strong early in life and become much weaker with age,” explains lead author of the study, Annika Karlsson, leader of the research group in the Department of Laboratory Medicine at Karolinska Institutet. “Our results show how the T-cell response evolves and changes over time and can guide future surveillance and vaccine development,” he adds.