The novel coronavirus has hit over 200 countries around the world. As the number of COVID-19 cases rises on a daily basis, experts and scientists are working to expand their knowledge of the disease and formulate the most efficient strategies for its containment.
Some crucial aspects, however, still remain unclear. With the UK and Germany reportedly considering the grant of ‘immunity passports’ to identify those who have recovered from COVID-19 (and are therefore presumably immune to it), the possibility of getting re-infected with the disease needs to be evaluated. Moreover, a bigger question needs to be answered: What does immunity even mean in the case of this relatively new respiratory illness?
Is COVID-19 Reinfection Possible?
Speaking to FIT, Dr Nivedita Gupta of the Indian Council of Medical Research (ICMR) had said, “There is insufficient data on the novel coronavirus to comment on the possibility of re-infection. It cannot be ruled out, but it is too preliminary to tell.”
Dr Naga Suresh Veerapu, Assistant Professor, Department of Life Sciences at Shiv Nadar University also told FIT that it is too early to comment on the possibility.
The Centers for Disease Control and Prevention (CDC) maintains a similar stance regarding immunity in the case of COVID-19. “The immune response, including duration of immunity, to SARS-CoV-2 infection is not yet understood. Patients with MERS-CoV are unlikely to be re-infected shortly after they recover, but it is not yet known whether similar immune protection will be observed for patients with COVID-19.”
While there is no definite yes or no, some preliminary studies and experiences from other coronavirus strains have shown that the possibility of reinfection is very limited.
A small study posted on medRxiv, experimented on four macaques monkeys and found that when two of them were exposed to the novel coronavirus twice in a row, they did not get infected with it the second time. The study’s senior author Dr Chuan Qin told Live Science, “According to our current study, the antibodies produced by the infected monkeys can protect the monkey from the re-exposure to the virus.”
While the research has its limitations and is yet to be peer-reviewed, its findings are crucial because humans tend to show a similar immune response to the virus as these primates.
Since SARS-CoV-2 (the novel virus’ official name) was only encountered a little over three months ago, studies on it are still ongoing. In such a scenario, looking at previous virus outbreaks can be helpful.
A study of over 170 people who had been infected by Severe Acute Respiratory Syndrome (caused by another strain of coronavirus, called SARS-CoV) found that SARS-specific antibodies were maintained for an average of two years in their bodies. This meant that SARS patients might be susceptible to reinfection three years after initial exposure. Similar findings were also arrived at for MERS, but since the number of patients affected was limited, the data obtained may be considered inadequate.
As for the seasonal coronaviruses that cause common colds, immunity seems to last for a shorter period of time, even if there are more number of antibodies, which is why getting a common cold is more frequent.
National Public Radio in the US quoted Stanley Perlman, Professor of Microbiology and Immunology, who said, “Based on other infections where you get a deep lung infection, you are usually protected against the second infection. If you just have a mild COVID-19 infection that involves your upper airway, maybe it will behave like a common cold coronavirus and maybe you can be reinfected again. We just really don't know. It's even hard to speculate."
What About the Reported Cases of ‘Re-Infection’?
Confusion regarding the probability of reinfection gained ground when such cases were reported from China, Japan and South Korea - even though only one case each has been reported from the latter two.
A study from China, for instance, looked at four medical workers in Wuhan who had recovered from the infection. They tested positive thrice consecutively after once having been released from quarantine. None of these patients passed on the infection to others, showing that even if recovered patients carry the virus, they may not be as contagious.
But if reinfection is unlikely (albeit possible), what would explain such cases?
Experts from around the world have theorised multiple alternate explanations for such relatively ‘rare’ cases. These include errors in testing and diagnosis, false negatives, low viral load of the disease post-recovery and early discharge, among others.
Chances of reinfection so soon after contracting the virus for the first time are extremely low because the body does develop antibodies. While we are not sure of how long the immunity lasts, it is highly unlikely that the duration is this little.
Dr Keiji Fukuda, director of Hong Kong University’s School of Public Health told Los Angeles Times, “If you get an infection, your immune system is revved up against that virus. To get reinfected again when you’re in that situation would be quite unusual unless your immune system was not functioning right.”
Another explanation could be that the virus level fell below what the tests could diagnose initially, but it revived later. In such scenarios again, the case is not so much of ‘re-infection’, but only of ‘resurfacing’ of the same virus that had not completely been cleared from the body in the first place.
Are ‘Immunity Passports’ a Good Idea Then?
According to a CNN report, UK’s Health Secretary Matt Hancock has suggested that Britons who’ve had the virus may be issued a certificate based on the antibodies that they now have in their bodies (can usually be detected around two weeks into getting the infection), making them presumably immune to COVID-19.
"We are looking at an immunity certificate, how people who've had the disease, have got the antibodies and therefore have immunity, can show that and get back as much as possible to normal life," he said. This could also take the form of a wristband, BBC reported later.
Researchers in Germany are exploring the idea by testing people for antibodies against COVID-19. According to Politico, the CDC has also begun conducting these blood tests to determine if a person has been exposed even without showing symptoms. India plans to test for antibodies on a large scale in hotspots to determine how wide the infection spread is.
The objective of granting immunity passports stems from letting people resume work after isolation and slowly getting things back to normal. But is such an approach reliable and safe, considering our lack of knowledge about the disease?
Hancock himself has said, "But as yet we're not going to bring them in because we don't know yet that the immunity is strong enough and there's still more science that needs to be done about the levels of immunity in people after they've had the disease. So it's only when we have the confidence that that's reasonable are we going to do that."
The issues here could be multiple. Firstly, this would require reliable antibody test kits to detect the presence of antibodies in people who were once infected, and these tests would have to be carried out at a considerably large scale among the general population. In fact, Hancock told UK broadcaster ITV that the government has not yet found an antibody that works. The plan, then, could be very ambitious to implement.
The strategy could perhaps be useful in getting health-care workers who were once infected back into the field to provide help and support to people in the hospitals. This was observed during the Ebola outbreak in West Africa when people who were deemed immune were able to contribute and help patients without using much PPE.
But apart from logistics, the doubt over its efficiency comes from the many unanswered questions about immunity.
Would getting antibodies detected in the test be enough to ensure complete immunity from the virus? More importantly, how long will this immunity last?
For instance, acquired immunity in the case of measles is lifelong, but with common cold or flu, it is usually seasonal.
The possibility of reinfections and what it would mean for our understanding of the virus and its mutation would have implications for vaccine development. Scientists are also turning to blood plasma from recovered patients to be used for currently infected people, with the hope that the antibodies in the former could help develop treatments for the disease (as they have in previous outbreaks).
But until these questions are answered, following precautions, conducting rampant tests to identify COVID-19 patients and implementing social distancing remain indispensable measures in the fight against the pandemic.
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