- Scientists still don't know if people who have recovered from the coronavirus can contract it again.
- Experts say people who have been infected probably develop immunity, but it's not clear whether it weakens over time.
- New blood tests can tell if people have had the virus by detecting antibodies — which is crucial in determining whether people self-isolating can return to work.
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There are still many unknowns about the coronavirus, but an important, lingering question is whether or not people who have recovered can get reinfected.
"We don't know very much," Matt Frieman, a researcher at the University of Maryland School of Medicine in Baltimore, told NPR.
"I think there's a very likely scenario where the virus comes through this year, and everyone gets some level of immunity to it," he added. "And if it comes back again, we will be protected from it — either completely, or if you do get reinfected later, a year from now, then you have much less disease."
Scientists are working to answer this question — which could play a crucial role in decisions about whether to let people who have recovered out of lockdown.
Immunity to the coronavirus
When your body encounters the new coronavirus, it has no built-in immunity. The immune system has to develop antibodies — proteins that fight a specific antigen.
Generally, once your body has antibodies that know how to fight off a particular invader, you can't get sick from it again. That's why someone who had chickenpox or got the vaccine won't get the disease twice.
But it doesn't always work that way — seasonal flu viruses mutate every year, which is why new flu vaccines are needed every year. In addition, some types of antibodies tend to weaken over time.
In the case of the new coronavirus, one report found that a tour guide in Japan recovered from the coronavirus, then tested positive for it again three weeks later. Doctors aren't sure if she was reinfected or had not fully recovered from the first infection.
A study from Chinese researchers on healthcare workers who recovered from SARS in 2002 found that the number of SARS antibodies peaked in patients' bloodstreams in 2004, and declined afterward until the study ended in 2015. (The study was released in the preprint server MedRx last month, but hasn't been peer-reviewed yet.)
These "antibodies have neutralization activities and provide protection against infections," the researchers wrote. They're an indicator that these recovered patients had some immunity to SARS, they added, but it's unclear if it's "complete protection" from reinfection years later.
Because the new coronavirus shares 79.5% of its genetic code with SARS (SARS is also a coronavirus), it's possible that antibodies for the new coronavirus might behave similarly.
In another study, a group of scientists infected rhesus macaques with the novel coronavirus, let them recover, then tried to reinfect them. The first infection gave some of the monkeys a mild illness, resulting in moderate pneumonia and weight loss, but the second did not seem to affect any of them. (The study is also a preprint on MedRx that is undergoing peer review.)
Antibody tests can tell you whether you've had the coronavirus
If people who recover from the coronavirus become immune, then it's even more crucial to know who has had the virus and who hasn't.
About 1% of coronavirus cases are asymptomatic, according to a study from the Chinese CDC, but many experts think the portion is actually higher because people with asymptomatic or very mild cases are not often tested nor reported.
Blood tests that find coronavirus antibodies could tell people whether they have had the virus before — even after they've recovered and even if they didn't ever show many symptoms. These antibody tests differ from the diagnostic tests used now. The current tests confirm active infections, whereas antibody tests would confirm whether people are recovering or have recovered from the virus.
This could be especially useful for people wondering whether it's safe to emerge from lockdown, given that a third of the world is under some kind of restriction on movement.
"Ultimately, this (antibody test) might help us figure out who can get the country back to normal," Florian Krammer, a professor at Mount Sinai's Icahn School of Medicine, told Reuters. "People who are immune could be the first people to go back to normal life and start everything up again."
University laboratories and medical companies are both rushing to produce antibody blood tests, and the US Food and Drug Administration has relaxed its rules to allow such tests to be produced faster.
According to The Guardian, at-home antibody coronavirus tests take 15 minutes. The UK government bought 3.5 million of them and is looking to distribute them to people who are self-isolating as soon as possible.
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