The study recruited 1343 people with known or suspected infection with COVID-19 in the New York Area. They divided them into groups with knowninfection (based on a positive test for active infection – a PCR test) or those with suspected infection (with symptoms, negative PCR).
Their key, exciting, headline result is that among the 624 people with known infection, only 3 of them did not seem to produce antibodies. That is, when they did their serology antibody tests, only 3 people did not show evidence of past infection with antibodies. The sample included many people with mild or moderate infection, suggesting that antibodies develop even without severe infection.
Although it got less coverage, another neat feature of this research is they followed people over time and tested them multiple times. This gave them a chance to see more about the course of the infection including how quickly people develop antibodies. They are able to say (for example) “our findings suggest that IgG antibodies develop over a period of 7 to 50 days from symptom onset and 5 to 49 from symptom resolution.” This helps researchers pinpoint when antibody tests could be used to detect infection (answer: at least a week after symptom onset, and possibly not until almost two months later).
Why is this Exciting?
In our Immunity Explainer we talk about a lot of the unanswered questions in COVID-19 immunity. One of the big ones is what share of people who are infected develop antibodies. Viruses differ in the extent to which antibodies are produced, and people differ in their antibody production. So far, we haven’t had enough data on COVID-19 to be clear on the answer in this case. Of particular interest was the question of whether people who had less severe infection would develop antibodies.
This study answers this question or, at least, provides a lot more of an answer than we had before. This is a big step. It’s also a very high quality study: the sample is large, they used the best available tests for antibodies (an ELISA test – see testing explainer for why that’s good) and the researchers were careful to follow people over time. Overall, lots to like. (We should note this study is not yet peer reviewed.)
What’s Still Unknown?
A lot. One may be tempted to think this shows that anyone who had COVID-19 cannot be infected again, but this is taking the results too far. We still do not know how long immunity lasts, which antibodies are most important and what concentration you need to prevent later infection. This is a hugely important and impactful first step, but certainly not the last.