The fourth round of antibody testing in New Delhi raised some interesting questions, and the results of the test were announced at a court hearing on Wednesday.
The study found that of approximately 15,000 people tested, 25.5% had Covid-19 antibodies. The test takes place in the third week of October. The results are almost the same as those of the third round of surveys, covering approximately 17,000 people in the first week of September, which indicates that 25.1% of the people surveyed have antibodies. The second round (about 15,000 tests conducted in August) showed that 29.1% of the people surveyed had antibodies. The first round was in late June and early July. Among the 21
This is not the way the results of the serum survey mean progress. Serum surveys (such as those conducted in Delhi) are a measure of the prevalence of infections (Covid-19 in this case), so immunity can be measured. Ideally, before reaching the level of herd immunity, the results should show an increase in prevalence or immunity. This is a safe level for most of the population because the virus cannot find enough people to infect it. However, making such assumptions will bring some trouble: First, Covid-19 antibodies do not seem to last. On the other hand, the presence of antibodies is not always necessary for immunity, just as the absence of antibodies does not indicate a lack of protection. Indeed, a serological survey conducted in Delhi in October found that 43.5% of people previously diagnosed with Covid-19 no longer have antibodies.
This is not entirely unexpected.
In late October, a study led by Imperial College London conducted three rounds of surveys between June and September, involving 365,000 people in England. The study showed that the number of people with Covid-19 antibodies increased over time. Decrease with passage. The British study actually found that the infection rate in all parts of the country has dropped, and it has dropped significantly between the first and third rounds. The study was conducted before the second wave of infections in the UK. This is probably also discovered by the Delhi study.
However, there is some controversy regarding the behavior of antibodies. According to a paper published in Science Immunology by American researchers in early October, including some researchers from Massachusetts General Hospital, and based on a study of 343 Covid-19 patients, they found that immunoglobulin G (IgG ) Antibodies, these antibodies usually provide lasting immunity that has been found in patients for up to four months (the study ended at that time). Other IgA and IgM variants were found 12 days after infection, but the duration did not exceed two months.
The second paper was also published in the same journal at the same time, but based on a study conducted by researchers at the University of Toronto in Canada, a similar conclusion was reached-IgG antibody levels reached a high level between two weeks and the second week. One month after infection, then it remains stable for at least three months. The study covered 439 people (not all of them have been tested, but all do have symptoms of Covid-19).
Interestingly, as pointed out by Dispatch 112 on July 23 (citing papers on the preprint server in late June), studies by Karolinska Institute and Karolinska University Hospital in Sweden have shown that many are asymptomatic or only show mild symptoms. Those infected with symptoms did not test positive. Although they have what researchers call a strong T cell response, they still have antibodies. The research was subsequently published in Cell. T cells are the fighting experts of the immune system (they remember viruses, even better), cells that can recognize and fight infection. This study (about 200 people) showed that twice as many people with Covid-19 antibodies have T cell immunity. This probably means that people who are asymptomatic or with mild infections will not produce these antibodies, or will disappear soon after the infection has passed, although (according to the Swedish study) they are still immune. Is that the result shown in Delhi? What does this mean in terms of the incidence of infection and immunity?