The world’s first confirmed cases of COVID-19 reinfection, recently documented in Hong Kong, as well as in the Netherlands and Belgium, have caused some people to wonder how the pandemic will ever come to an end if there is no way to become immune to the novel coronavirus. While the concern is understandable, those cases also bring their share of good news.
First, those few confirmed cases of reinfection, while isolated, teach us a few things about SARS-CoV-2, the virus responsible for COVID-19, says Dr. Leighanne Parkes, an infectious disease specialist and microbiologist at the Jewish General Hospital in Montreal.
Dr. Parkes, who is also an associate professor at McGill University’s Department of Medicine, is currently collaborating in a McGill-led clinical research initiative to test the efficacy of existing drugs against COVID-19.
She says it’s not uncommon for a patient to receive a new positive test result after having recovered from COVID-19 and tested negative.
“We see this quite frequently. We’ve even seen a few locally within Quebec,” she told HuffPost Canada. “You have individuals who were positive many months ago and sort of have this long persistent shedding of low levels of virus that is detected by our tests.”
But this “prolonged low-level viral shedding” is intermittent, and positive test results might come and go for several months after someone has recovered. It’s one of the reasons why the U.S. Centers for Disease Control (CDC) issued new testing guidelines last month, stating it isn’t useful to retest someone within three months of their recovery.
Watch: Find out more about the updated testing guidelines. Article continues below.
What’s new in the case of the Hong Kong patient is that scientists were able to confirm that the man suffered a new infection, and that his positive result wasn’t due to lingering effects of the initial one.
The 33-year-old man was diagnosed with COVID-19 for the first time in late March. He had a cough and a fever, as well as headaches and a sore throat. His recovery was confirmed with two negative tests.
Roughly four months later, on Aug. 15, he tested positive again, this time after a routine test at Hong Kong International Airport following a trip to Europe.
Scientists were able to take the viruses from both the March and August samples and sequence them, basically creating a genetic blueprint of the genetic code the man had in his nose each time he tested positive, Dr. Parkes explains.
“They looked at them side by side and saw that they were from two different strains,” she said. “That’s how they proved that it wasn’t the same virus still shedding, but a completely different virus.”
The second time, the man showed absolutely no symptoms of COVID-19.
While the prospect of someone walking around with COVID-19 without any hint of a symptom and all the reasons to believe they’re safe can be unnerving, it might actually be good news.
“It shows that the immune response was quite strong [the second time],” says Benoit Barbeau, a virologist who teaches at Université du Québec à Montréal.
“Basically, it tells us that the person was infected, had an immune response and produced antibodies,” he explained. “Even though the quantity of antibodies decreased, the person was still protected when they got reinfected that second time.”
For Barbeau and Parkes, this could mean that while immunity to the novel coronavirus doesn’t last very long, the initial infection could continue to provide a certain level of protection even once the antibodies are mostly gone.
“It’s a pretty good sign. It could mean that someone who went to ICU the first time around maybe wouldn’t get so sick the second time around,” Dr. Parkes posits.
Don’t bank on natural immunity
Even though scientists in Hong Kong did a great job of confirming that reinfection to COVID-19 is possible, one very important question remains: was that man contagious or not the second time?
The absence of symptoms could mean that the person was less infectious, Barbeau theorizes. It’s possible that their immune response was effective enough to prevent the virus from replicating too much, meaning that the quantity of virus found in the body — and ready to be expelled through droplets — could be lower.
He believes “it’s a strong probability.”
“Recent studies have shown that antibodies don’t remain in very high quantities after only a few weeks.” Benoit Barbeau, professor in biological sciences and virology expert
The tests that were done on the Hong Kong patient’s newest sample seemed to indicate a large amount of virus present in his body when the sample was taken, though that measure is “imprecise,” Dr. Parkes says.
Researchers didn’t culture the second sample, she adds, so we don’t know if the virus present is capable of infecting another person, regardless of the amount.
Without any data showing that reinfected people aren’t contagious, this study gives us another hint that the idea touted by some countries of distributing “COVID passports,” certificates that would allow people to resume a maskless life free of social distancing after recovering from coronavirus, could be an unmitigated disaster.
“We already knew that this practice probably wasn’t the best,” Barbeau says. “Recent studies have shown that antibodies don’t remain in very high quantities after only a few weeks.”
Even if the science has been clear on this for a little while, the general public seems to hang on to the idea that having COVID-19 protects you from another infection, at least for some time. A few days after publishing their new guidelines, the CDC had to issue a statement specifying that it did not mean a person was immune to reinfection for three months.
“Contrary to media reporting, this science does not imply a person is immune to reinfection with SARS-CoV-2, the virus that causes COVID-19, in the 3 months following infection,” the CDC wrote on Aug. 14. “The latest data simply suggests that retesting someone in the 3 months following initial infection is not necessary unless that person is exhibiting the symptoms of COVID-19 and the symptoms cannot be associated with another illness.”
What does that mean for the vaccine?
So, COVID passports are not happening. And neither will herd immunity, at least not natural herd immunity.
That isn’t to say, however, that herd immunity can’t be achieved through a vaccine, Barbeau and Dr. Parkes both caution. It certainly does not mean that we will have to get a new shot every three months once a vaccine is available.
“Vaccination is inherently different from natural immunity in many, many ways,” Dr. Parkes insists.
That’s because the vaccine won’t have all that much in common with SARS-CoV-2, Barbeau explains.
“When you’re infected naturally, the virus’s aim is to infect you and then move on to another host to spread,” he says. “It doesn’t want the immune response to be too effective.”
In order to create a vaccine, scientists will focus on certain components of the virus in order to trigger an immune response that’s effective, selective and long-lasting.
“It’s important to remember that vaccine immunity will have attributes and added value that will make it a lot more effective than a natural infection.”
The moral of the story
While these new studies on reinfection open the door to more questions, the main takeaway is very clear for Parkes: people who have had COVID-19 should continue to remain vigilant.
If there is a risk of continued reinfection, we have to persistently remain vigilant. Dr Leighanne Parkes, microbiologist
“The feeling that ‘oh I already had COVID, I’m safe, I can lower my guard’ is a dangerous thought, both from a personal and a public health standpoint,” the infectious disease specialist warns.
She sees those confirmed cases of reinfection as a stark reminder that “horizontal sanitary measures” — the ones that are meant to protect everyone, whether or not they are showing symptoms — are crucial.
“If there is a risk of continued reinfection, we have to persistently remain vigilant,” she says, cautioning against COVID fatigue.
It means that Canadians will need to be “very careful of what activities we open up to that are potentially high risk,” she warns.
Proper masking, physical distancing and appropriate cleaning of surfaces are more important than ever, she believes, “because we can’t necessarily fall back on herd immunity to rip away all these precautions and proceed with life as it was in the pre-COVID era.”
This article originally appeared on HuffPost Canada and has been updated.