Newly released research indicates that human immune system cells store information about the coronavirus so that they can fight it off again, should it come back.
Dr Deepta Bhattacharya, an immunologist at the University of Arizona, said disease-fighting antibodies, as well as immune cells called B cells and T cells, which recognise the virus, appear to persist months after infections have resolved.
"This is an encouraging echo of the body's enduring response to other viruses. Things are really working as they are supposed to," Bhattacharya, an author on one of the new studies, which has not yet been peer-reviewed, said.
To the immune system, not all germs are equally memorable. But our body's cells seem to be seriously studying up on the coronavirus. Scientists who have been monitoring immune responses to the virus are now starting to see encouraging signs of strong, lasting immunity, even in people who developed only mild symptoms of coronavirus.
Human body working
However, for now, researchers cannot forecast how long these immune responses will last.
But Dr Marion Pepper, an immunologist at the University of Washington, said many experts consider the data a welcome indication that the body's most studious cells are doing their job.
"This will have a good chance of fending off the coronavirus, faster and more fervently than before, if exposed to it again. It is exactly what you would hope for," Pepper, an author on another of the new studies, which is currently under review at the journal Nature, said.
However, Pepper said for now, lasting protection against reinfection cannot be fully confirmed until there is proof that people who encounter the virus a second time actually keep it at bay. But, she said, the findings are helpful in quelling concerns over the virus' ability to dupe the immune system into amnesia, leaving people vulnerable to repeat bouts of disease.
According to the World Health Organisation (WHO), there is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection.
Dr Monica Musenero, the senior presidential advisor on epidemics, explained that the development of immunity to a pathogen through natural infection is a multi-step process that typically takes place over one to two weeks.
The body responds to a viral infection immediately with a non-specific innate response to slow the progress of the virus and may even prevent it from causing symptoms.
"This non-specific response is followed by an adaptive response where the body makes antibodies that specifically bind to the virus.nThe body also makes T-cells that recognise and eliminate other cells infected with the virus.
"This combined adaptive response may clear the virus from the body, and if the response is strong enough, may prevent re-infection by the same virus. This process is often measured by the presence of antibodies in blood," Musenero said.
Should this be confirmed with the coronavirus, it will mean that infection with it may boost immunity for survivors and when they become many, create their immunity that will eventually get rid of the virus from the community.
According to WHO, reviewed evidence on antibody responses to COVID-19 infection shows that people= who have recovered from infection have antibodies to the virus.
However, some of these people have very low levels of neutralising antibodies in their blood. That is why, if new study findings reveal that COVID-19 infection confers immunity to subsequent infection by the virus in humans, it will be good news for the public.
The problem seems to be that survivors may lose these antibodies to coronavirus sooner than they should be helping with lasting protection.
According to immunology, antibodies have an expiration date. Because they are inanimate proteins and not living cells, they cannot replenish themselves and so disappear from the blood just weeks or months after they have neutralised the threat. Most of the B cells that produce these early antibodies die off as well.
But, even when not under siege, the body retains a battalion of longer-lived B cells that can churn out virus-fighting antibodies en masse, should they prove useful again. Some of them patrol the bloodstream, waiting to be triggered anew; others retreat into the bone marrow, generating small amounts of antibodies that are detectable years, sometimes decades, after an infection is over.
Several studies, including those led by Bhattacharya and Pepper, have found antibodies capable of incapacitating the coronavirus lingering at low levels in the blood months after people have recovered from COVID-19.
"The antibodies decline, but they do not disappear. They settle in what looks like a stable nadir," and are observable about three months after symptoms start. The response looks perfectly durable," Bhattacharya said.
A lot about coronavirus remains unknown. Although these studies hint at the potential for protectiveness, they do not demonstrate protection in action, said Cheong-Hee Chang, an immunologist at the University of Michigan who was not involved in the new studies.
"We still need more research into this. Humans are so heterogeneous. There are so many factors coming into play," Chang said
Pepper responded saying tracking long-term human responses will take time. Good immune memory, she added, requires molecules and cells to be abundant, effective, and durable — and scientists cannot yet say all three conditions have been definitively met.
Bhattacharya also said they will monitor people whose bodies settle into their postcoronavirus state.
"There is no shortcut here," Bhattacharya said. "We just have to follow it out."
SmitaIyer, an immunologist at the University of California, was quoted by The Times Online as saying the findings are promising.
"This calls for some optimism about herd immunity, and potentially a vaccine," he said.
Research groups around the world are continuing to study the entire range of responses.
What has been observed in people who fight off mild cases of COVID-19 might not hold true for hospitalized patients, whose bodies struggle to marshal a balanced immune response to the virus, or those who were infected but had no symptoms at all.
For herd immunity to work, the vast majority of the cases which remain asymptomatic must retain the protective immune response for some good time.