Coronavirus antibody tests might come back negative for people who had mild cases
Coronavirus immunity tests might return false negatives for people who experienced a mild or asymptomatic case of COVID-19.
The conclusion comes from a new Oxford study that looked at the sensitivity ratings of antibody tests on patients who might have had the virus.
The researchers found that a large number of people might get negative results in antibody tests despite possibly having had the illness at some point in the past few months.
COVID-19 immunity is one of the most important topics of research right now, but the novel coronavirus is too new to give us a definitive answer to the most important question we have: Is reinfection possible? The management of outbreaks and future vaccination policies might hinge on the answer. Researchers think that the novel coronavirus will behave just like other human coronaviruses when it comes to immunity. We’ll get six to twelve months of protection , but then reinfection could be possible.
Separately, researchers are looking to measure the actual number of COVID-19 cases in a community by performing antibody tests. These are specific “witnesses” of the infection that prove the immune system has eliminated the coronavirus and is ready to block it again upon a second encounter. But recent studies have shown that antibodies can vanish from the bloodstream as soon as two to three months after the first infection . The immune system would still have specialized T cells to fall back to in case of a second contact with the virus, so the immunity is not lost when the antibodies are gone . But antibody tests would not pick up T cells. That’s a separate, more difficult test.
A new study now indicates that antibody tests fail to detect people who had mild coronavirus cases, which could become a real problem in a variety of situations. It’s not that people who experience mild cases of COVID-19 do not develop an immune response. But the current tests have been created using samples from symptomatic patients, who were often hospitalized for treatment.
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The Oxford study enrolled more than 9,000 healthcare workers and showed that a significant number of people tested negative for antibodies despite probably having had the virus. The researchers used a particular symptom that’s been associated with COVID-19, and that’s the sudden loss of smell and taste. Several other studies showed why the phenomenon occurs and proved that it’s likely to test positive for COVID-19 after experiencing it. Not all people who get infected experience the symptom. That’s why PCR tests are still needed to diagnose the illness correctly.
The Oxford study showed that of the 903 people who tested positive for antibodies on one test, 47% of them reported a loss of smell or taste. But there also was a group of subjects whose...