What is the best way to measure rates of covid immunity?
In my previous post on the covid pandemic I mentioned that the body’s main defence against viruses is T-cells, not antibodies, and that the only reason we test for antibodies instead in clinicial practice is because it is easier and cheaper. I also ventured a hypothesis that the levels of population immunity are much higher than is being found in the antibody tests, and that this is because lots of people who don’t have antibodies do have covid specific T-cells. It turns out that this hypothesis is supported by new evidence. A study carried out at Karolinska Institutet (where I went to medical school), which is still awaiting publication, looked at the presence of both antibody-based and T-cell specific immunity to covid among people in Stockholm. The data was collected during May. The first covid fatality in Sweden was in mid-March, so at that point covid had been raging for about two months. The study was funded by Karolinska Institutet, the Swedish Research Council, and a number of private foundations and charities. The authors reported no conflicts of interest.
Study participants were recruited in to five distinct cohorts, with a total of around 200 individuals: The first cohort was made up of patients who had had a mild infection and recovered. Most of these (78%) had not been sick enough to be admitted to hospital. The few that had been admitted had at most required one liter of supplemental oxygen. This was the “mild convalescent” cohort. The second cohort was the “severe convalescent” cohort, which consisted of patients who had been sick enough to require larger amounts of oxygen and/or mechanical ventilation, and then recovered. The third cohort was made up of family members of people in the mild convalescent and severe convalescent group. In order to qualify to be part of this cohort, participants had to have spent time in the same household as the sick family member when they were sick, but not themselves been diagnosed with covid 19. This was the “exposed family members” cohort. The fourth cohort consisted of a random sample of people who donated blood in May 2020, while the fifth cohort consisted of a random sample of people who donated blood in July to September of 2019. The fifth cohort served as a form of control group, since the blood was collected before the beginning of the pandemic. Although each of the cohorts is a bit small for my liking, it is an interesting mix, which can potentially answer some important questions about how the immune system reacts to covid, and how prevalent covid was at this point in time in Stockholm.
https://sebastianrushworth.com/2020/08/08/what-is-the-best-way-to-measure-rates-of-covid-immunity/
Robust T cell immunity in convalescent individuals with asymptomatic or mild COVID-19
https://www.biorxiv.org/content/10.1101/2020.06.29.174888v1.full