The question of how we gain immunity to the novel coronavirus remains a very pressing one, and one to which the answer is still somewhat elusive. Surely, people who defeat the virus must develop some type of antibodies — that’s what defeating the virus means in the first place.

These antibodies also don’t just go away immediately (they might fade after a few months or years, but that’s a different matter). So then why are people testing positive again, days after they were cleared?

South Korea has been wildly hailed as one of the role models in dealing with the novel COVID-19 pandemic. Although it was one of the first countries to report an outbreak, and despite initial uncontrolled spread, South Korea managed to handle the outbreak without imposing draconic measures. Right now, the country doesn’t have a major lockdown, and yet only reports 20-30 new cases every day.

However, a startling number emerged from Korea recently: at least 116 people initially cleared of the new coronavirus had tested positive again.

What this means

First of all, there is a strong case to say that some type of immunity is developed in the vast majority of people. But given the low number of new cases in Korea, 116 reinfections doesn’t sound like a small number at all — unless, it’s not reinfections we’re dealing with.

There are two likely explanations for this (which are not mutually exclusive). The first is that we are simply seeing false positives. No test is perfect, especially for a disease as novel as COVID-19. It could also be that the test is picking up a low amount of virus that is inactive. This is very likely and has been highlighted as a possibility before. However, this does not explain the full picture, as some people who initially test negative start developing visible symptoms and clearly have an ongoing infection.

Which brings us to the second possibility: false negatives. RT-PCR testing is most useful when it is positive, but when it is negative, it doesn’t necessarily mean that the person doesn’t have the disease.

In a brief statement, the World Health Organization has said that they working with Korean experts to get to the bottom of this problem.

“We are aware of these reports of individuals who have tested negative for COVID-19 using PCR (polymerase chain reaction) testing and then after some days testing positive again,” the statement said.

“We are closely liaising with our clinical experts and working hard to get more information on those individual cases. It is important to make sure that when samples are collected for testing on suspected patients, procedures are followed properly . “

Figuring out how immunity for the novel coronavirus works is essential for our long-term strategy against it. Previous research has shown that the virus has a relatively low mutation rate, which could indicate that a vaccine effect would be long-lasting, but this is far from proven at this moment.