By Apoorva Mandavilli
As the number of people infected with the coronavirus continues to rise (already over 450,000 worldwide), and more than a billion people are locked up in their homes, scientists continue to struggle with one of the most pressing issues of the pandemic: Do people who survive the infection become immune to the virus?
The answer is that it seems that yes, but that there is important questions that are still unanswered. This is important for several reasons.
People immune to the virus could leave their homes and help strengthen the workforce until a vaccine is available, for example. In particular, health workers known to be immune may continue to care for the seriously ill.
Increasing immunity in the community is also the formula by which the epidemic is defeated: as fewer and fewer people become infected, the coronavirus will lose strength, and even the most vulnerable citizens will remain more isolated from the threat.
Immunity too can bring early treatment. Antibodies collected from the recovered bodies can be used to help those struggling with the disease caused by the coronavirus, called COVID-19.
Last Tuesday, the Food and Drug Administration (FDA) approved the use of plasma from recovered patients to treat some serious cases. A day earlier, Governor Andrew Cuomo announced that New York would be the first state to begin testing the serum from people who have recovered from COVID-19 to treat those who are seriously ill.
“It is a trial for people who are in serious condition, but the New York State Department of Health has been working on this with some of the best healthcare agencies in New York, and we believe that there are reasons to be optimisticCuomo said.
The path of immunity
The body’s first line of defense against an infectious virus is an antibody called immunoglobulin M, whose work is watch the body and alert the rest of the immune system to the entry of intruders such as viruses and bacteria.
Days after infection, the immune system refines this antibody into a second type, called immunoglobulin G, which is exquisitely designed to recognize and neutralize a specific virus.
This refinement process can take up to a week; Both the process and the potency of the final antibodies can vary. Some people make powerful antibodies that neutralize an infection, while others mount a smoother response.
Antibodies generated in response to infection by some viruses – polio or measles, for example – provide a lifetime of immunity. But the antibodies against coronaviruses that cause a common cold last only one to three yearsAnd that may also be true for this new relative who has just appeared.
A study in macaques infected with the new coronavirus suggested that once infected, monkeys produce neutralizing antibodies and resist further infection. But it is unclear how long monkeys, or people infected with the virus, remain immune.
Most people who became infected during the SARS epidemic – that virus is a close relative of the coronavirus, called SARS-CoV-2 – developed long-term immunity, lasting for eight to 10 years, Vineet D said Menachery, virologist, University of Texas Medical Branch at Galveston.
Those who recovered from MERS, another strain of coronavirus, had much shorter protection, Menachery said. People infected with the new coronavirus may have an immunity that lasts for at least one to two yearsHe added: “Beyond that, it is impossible to predict.”
Still, even if antibody protection were short-lived and people were reinfected, the second attack with the coronavirus would likely be much milder than the firstsaid Florian Krammer, a microbiologist at the Icahn School of Medicine at Mount Sinai in New York.
Even after the body stops producing neutralizing antibodies, a subset of immune memory cells can effectively reactivate a response, he noted.
“You would probably get a good immune response before becoming symptomatic again, and it could really slow down the course of the disease, “Krammer said.
A crucial question is whether children and adults with only mild symptoms continue to generate a response strong enough to remain immune to the virus until a vaccine is available.
Dr. Marion Koopmans, a virologist at Erasmus University Rotterdam, and her team have examined antibody responses in 15 infected patients and healthcare workers.
The researchers are also using stored blood samples from about 100 people known to be infected with one of the four coronaviruses known to cause the common cold.
If those samples also show some immune response to the new coronavirus, Koopmans said, that might explain why some people, like children only have mild symptoms. They may have antibodies against some of the other coronaviruses that ultimately have some degree of effectiveness against the new one.
The fastest way to assess immunity is a blood test that looks for protective antibodies in the blood of people who have recovered. But first you have to be tested.
Antibody tests are used in Singapore, China, and a handful of other countries. But they are just coming to market in much of the West.
Last week, Krammer and his colleagues developed an antibody test that can be expanded in “days or weeks,” he said.
The team validated the test in blood plasma taken from three patients with COVID-19. Investigators are seeking rapid FDA approval.
© 2020 The New York Times