05/27/2020
Yes, You Develop Some Immunity to Covid-19. The Question Is, How Much?
Experts say it would be ‘extremely bizarre’ if people didn’t develop some immunity to Covid-19
A mong the many lingering questions surrounding the coronavirus and its long-term impact on the body is the likelihood of developing immunity after recovering from the virus. And if people do develop immunity, how long does it last? An important step toward reopening the country, determining who has immunity against reinfection, and what level of protection immunity confers can help establish the risk of sending large groups of people back to work.
Back in March, Anthony Fauci, MD, the director of the National Institute of Allergies and Infectious Diseases and the country’s leading infectious disease expert, said in an appearance on The Daily Show with Trevor Noah he would be “willing to bet anything that people who recover are really protected against reinfection.” A few weeks later, the World Health Organization released a statement explaining there existed “no evidence that people who have recovered from Covid-19 and have antibodies are protected from a second infection.”
Still, dozens of new serological tests designed to detect the presence of antibodies — that is, to figure out if you were exposed to the virus and your immune system produced antibodies, or proteins that ward off future infection — were rolled out, with varying degrees of accuracy. Studies of people recovered from Covid-19 showing low or no levels of antibodies continue to highlight how little scientists actually know about how long antibodies last and why we don’t all make the same amount.
Despite all the swirling uncertainties and inconsistencies surrounding immunity, scientists do agree that humans develop immunity to Covid-19. Long-term research is necessary to paint a clearer picture of the level of antibodies necessary to confer immunity and the duration of protection.
“I feel like this isn’t going to be the virus that breaks the immunology textbook,” says Michael Mina, MD, PhD, an assistant professor of epidemiology at Harvard T.H. Chan School of Public Health. “How durable that immunity ends up being and how protective it ends up being, that’s what we need to figure out. But we absolutely know that this virus leads to immunity in most people.”
When our body’s immune system is attacked by a virus, white blood cells create antibodies to fight off the invading infection. If we’re exposed to this same virus again, usually, our immune system remembers the threat and creates new antibodies, eliminating the infection before we start to feel sick. In terms of the body’s antibody response to Covid-19, a new study showed that out of 285 people who tested positive for Covid-19, all of them developed antibodies within 19 days of symptom onset.
“I feel like this isn’t going to be the virus that breaks the immunology textbook.”
While little is known regarding our immune response to Covid-19, scientists are able to look at how our body wards off other coronaviruses, of which there are seven — four that cause the common cold, and three others: MERS-CoV, which causes Middle East respiratory syndrome (MERS), SARS-CoV, which causes severe acute respiratory syndrome (SARS), and SARS-CoV-2, which causes Covid-19. Among people who recovered from SARS, antibodies were present for about two years post-illness, according to a 2007 study, suggesting reinfection may be possible three years after initially contracting the virus. In a 2016 study of three SARS-recovered patients, SARS-specific T-cells, which fight the virus, were found up to 11 years post-infection. Antibodies were found in people who recovered from MERS almost three years after getting sick, according to a 2016 study. And a new preprint study examining the coronaviruses which cause the cold found that people were frequently reinfected by the same virus more than once over the span of a year, indicating immunity is rather short-lived.
“We don’t know if this virus is actually that different from those seasonal coronaviruses in many ways,” Mina says. Would any novel coronavirus have a similar devastating effect as this one? “It could be that by the time you become old in our population, you’ve already seen these seasonal coronaviruses many times and you’ve developed immunity,” he says.
Since all Covid-19-specific studies are extremely short-term (as the virus has only been present for a few months), it will be years until scientists can say definitively if the immune response for Covid-19 is similar to that of other coronaviruses.
“You can produce antibodies that protect against MERS for up to three years,” says Nicolas Vabret, PhD, an assistant professor of medicine, hematology, and medical oncology at the Icahn School of Medicine at Mount Sinai. “This provides some kind of basis for scientists to look for in the case of Covid-19. We need to look at patients in two years to know, for example, if they would have the same length of antibody protection.”
As for short-term Covid-19 immunity research to date, antibodies were found two weeks post-recovery in a recent study, suggesting protective immunity lasts for at least up to two weeks. In another study, researchers found people with Covid-19 contained two types of T-cells that suggest immunity — helper T-cells and virus-specific killer T-cells — though the results do not ensure protection from reinfection. According to a preprint study, scientists studying the Covid-19 immune response in monkeys found the primates did not get reinfected after being exposed to a virus a second time after recovering from the initial illness.
It would be weird for someone who’s recovered from the virus to not have some layer of immunity.
The presence of antibodies doesn’t outright ensure immunity. Out of the five types of antibodies, neutralizing antibodies block infection. A new preprint study, however, discovered neutralizing antibodies in all surveyed patients six days after a positive Covid-19 test result.
“It’s been shown that at least some people that have had Covid-19, they do develop neutralizing antibodies,” says David Corry, MD, a professor of immunology, allergy, and rheumatology at Baylor College of Medicine. “Does a neutralizing antibody response in a test tube in a laboratory, does that translate into real-world protection after viral exposure? We don’t know the answer to that either.”
To know who’s actually been exposed, antibody tests will need to be more accurate than they presently are, Corry says. Even if a person who tested positive for Covid-19 received a test result that’s negative for antibodies, it could be the fault of an unsound test. “Their sensitivity is lacking,” Corry says of some antibody tests being used. “Their test comes back, you do not have antibodies to this test when in fact you do. If you used a more sensitive test you would’ve found the antibodies. You are probably protected.”
Because immunity duration is still unknown, it’s still possible people who have recently recovered from Covid-19 could get reinfected, though it’s not considered very likely. While early reports surfaced of people who were believed to be reinfected, new data from Korea shows that the people who have tested “re-positive” were not actually infectious.
Ultimately, while many unknowns remain surrounding immunity, one aspect remains constant: Experts believe immunity to Covid-19 exists. It would be weird for someone who’s recovered from the virus to not have some layer of immunity.
“That would be extremely bizarre and no one is thinking that is true,” Corry says. “Certainly people are developing immunity and the only question is how effective is that immunity after infection.”
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