On Thursday, a Delhi policeman was reported with a case of the novel coronavirus 're-infection', raising the all-important question of whether a recovered patient can contract the infection again. The policeman, 50, had tested positive for the virus in May and was treated at between May 15 and 22. Thereafter, he had tested negative and resumed duty.
However, on July 10, he again felt unwell with a fever and dry cough and got himself tested on July 13. The report came positive through the rapid antigen test as well as the RT-PCR test, according to reports; the policeman, who has no other underlying ailment, complained of chest pain on July 16 and was admitted to the hospital.
Dr Rajesh Chawla, Senior Consultant, Respiratory and Critical Care Medicine, Apollo Hospitals, told news agency PTI: "The first time he was tested for coronavirus, he had no symptoms. The second time the policeman was tested for antibodies too, but it was found that he did not have antibodies". Antibodies are the proteins utilised by the immune system to neutralise foreign invaders and pathogens.
Why is this case important?
Similar cases of purported 're-infection' have been reported across the world. Earlier this week, a similar case had surfaced in the national capital after a nurse employed at a civic-run dedicated COVID-19 hospital had tested positive again after recovering. However, the municipal authorities had claimed there was nothing to worry as it is ostensibly the dead virus left in her body from the previous infection. Reports had claimed there were similar re-infection incidents in Kerala, when two expats reportedly tested positive again after they recovered once. Cases of similar re-infection have also been reported across China and South Korea.
Moreover, there is a very instinctive idea embedded in the public mindset that, once it comes and goes, the body attains an automatic immunity to the coronavirus. Some countries had even mooted the idea of 'immunity passports'. Individuals in possession of an 'immunity passport' could be exempt from physical restrictions and may return to work, school and daily life. The rationale behind certifying people immune is the production and presence of antibodies against the virus.
But, as scientists and experts have testified, the novel coronavirus is much trickier.
What are the likely causes of these reported cases of 're-infection'
There could be a multitude of reasons for the same.
It might not have been a case of re-infection at all. The patient could have tested a false positive upon admission, or he could have tested false negative upon discharge. Both these are reasons why the World Health Organisation (WHO) stresses on maximum reliability and accuracy in testing procedures (combined with speed) across the globe.
Another reason could be the presence of dead or inactive remnants of coronavirus from the previous infection, which are not dangerous because they remain dormant.
A third reason could be that the right level of antibodies was not developed against the virus which meant that when the patient was exposed again, he got reinfected.
According to Harvard Global Health Director Ashish Jha, who spoke to US PBS in early July: "This [re-infection] has been an ongoing concern. We have been looking at antibodies, and sometimes antibodies wane after a few months. Here is what I know: At least in the short term, re-infection is not common. It is probably rare. Most of the case of what we see vis-a-vis reinfection can be explained by problems in testing, or [inactive remnants] fragments of the virus."
The scientific debate over our immunity, and will vaccines work?
First, let us see how our immunity works. According to the WHO, The development of immunity to a pathogen through natural infection is a multi-step process that typically takes place over 1-2 weeks. The body responds to a viral infection immediately with a non-specific innate response in which macrophages, neutrophils, and dendritic cells slow the progress of virus and may even prevent it from causing symptoms. This non-specific response is followed by the body preparing antibodies that specifically bind to the virus. These antibodies are proteins called immunoglobulins. The body also makes T-cells that recognise and eliminate other cells infected with the virus. This is called cellular immunity. This process is often measured by the presence of antibodies in blood.
Some scientists have raised a red flag over the exponential waning of the coronavirus antibodies. According to a research conducted by University of California Los Angeles (UCLA) scientists, in people with mild cases of COVID-19, antibodies against the novel coronavirus may drop sharply over the first three months after infection.
According to the study, the levels may decrease by roughly half every 73 days; if the declining antibody levels sustained at that rate, they might disappear within about a year. Previous studies had suggested that antibodies which block the novel coronavirus are short-lived, but the rate at which they decrease has not been carefully defined. According to the scientists, the current research, published in the New England Journal of Medicine, is the first to carefully estimate the disappearance rate of antibody proteins which are part of the body's humoral immunity. "Our findings raise concern that humoral immunity against SARS-CoV-2 may not be long lasting in persons with mild illness, who compose the majority of persons with COVID-19," the scientists wrote in the research.
According to the scientists, the findings may also have implications for the durability of antibody-based vaccines. Similar concerns had been raised earlier. "The biggest challenge [for vaccines] would be the longevity of the [neutralising] antibodies,” Sunit K. Singh, professor and head, molecular biology, Institute of Medical Sciences, Banaras Hindu University, had told THE WEEK. In SARS-CoV-2, antibodies are known to fade between three-six months, as reported by various studies, he said. “So what would be the fate of protection induced by a vaccine once the antibody response vanishes or is reduced? A virus of this kind will certainly need an attack from both sides—the antibodies and T-cells,” he added.
However, other scientists have argued that waning antibodies don't mean protection is gone, or that it won't be possible to develop an effective vaccine. Infection with this coronavirus does not necessarily generate lifetime immunity, but antibodies are only part of the story, according to experts.
The immune system remembers how to make fresh antibodies if needed and other parts of it also can mount an attack. Antibodies are proteins that white blood cells called B-cells make to bind to the virus and help eliminate it. "The earliest ones are fairly crude but as infection goes on, the immune system becomes trained to focus its attack and to make more precise antibodies," according to researchers. Apart from antibodies, other parts of the immune system also help confer protection. Besides churning out antibodies, B-cells develop a memory so they know how to do that again if needed. They would get called into action very quickly when there's a new exposure to the virus. Other white blood cells called T-cells also are better able to attack the virus the next time they see it.
"Although circulating antibodies may not last long, what we need to know is if and how people remake antibodies if exposed to the coronavirus again and if they protect against another infection," Alison Criss, an immunologist at the University of Virginia, told AP. "We also need to know if there is a protective T-cell response that reappears."
Vaccines, which provoke the immune system to make antibodies, might give longer-lasting protection than natural infection because they use purified versions of what stimulates that response, she noted.
-Inputs from AP via PTI
