Scientists examining the coronavirus and the impacts of COVID-19 on the human body are scrambling to understand whether people are at risk of infection even if they have already contracted and recovered from the virus.
The question was thrown into stark relief over the weekend, when the World Health Organization (WHO) warned governments against issuing “immunity passports” to those who have recovered from the illness so that they could then return to work. The WHO said not enough is known yet about how the virus leaves the human body.
“There is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection,” the WHO said.
The answer has substantial ramifications for the global battle to stop the pandemic spread of the virus. If someone who has recovered develops antibodies that would fend off a second round, the coronavirus would eventually run out of victims to infect and would slowly die out.
But if recovery does not convey immunity, the virus could hypothetically never run out of potential fuel, and subsequent waves of viral infection could sweep over humanity for months or years, costing millions of lives and untold economic devastation. A virus that does not convey immunity would also pose a huge challenge to the teams around the world racing to come up with a vaccine.
Experts said a careful reading of the WHO’s scientific brief shows that the agency is waiting until it has iron-clad knowledge of what comes after someone is infected — there may not be evidence that someone cannot be infected a second time, but there is also not yet the evidence that someone can be infected again. That cautious approach may have sent the wrong message.
“They were trying to be extremely cautious about what we know and don’t know, and they were trying to avoid giving people false hope about long-term immunity,” said Nita Bharti, a biologist at the Center for Infectious Disease Dynamics at Penn State. “The message that ended up being received was not the one they intended to send.”
Some early studies seem to suggest that the coronavirus leaves behind antibodies that have made close relatives to humans such as macaques immune, at least in the short run. Two studies of macaques that had been infected, recovered and then exposed to the virus again failed to find any monkeys who got sick a second time.
“In general, we would not expect potential for immediate reinfection. That would be novel as hell,” Bharti said.
But different viruses convey different levels of immunity. Those who contract a common virus like chicken pox can remain immune for life. Vaccines against the measles can give humans immunity for decades. And someone who recovers from a common cold — potentially caused by a different, more ordinary strain of coronavirus — might have some protection against that same virus for a year or so.
Where the coronavirus lands on that broad spectrum is not yet known.
“There’s some level of protection” conveyed by the current strain of the coronavirus, said Michael Osterholm, director of the Center for Infectious Disease Research and Prevention at the University of Minnesota. “For how long, for how complete, we don’t know.”
Some of the WHO’s caution may reflect early studies out of China and South Korea, which suggested that some people who had recovered might have contracted the virus a second time. But those countries are conducting so many tests that they may have naturally registered some inaccurate results, and none of those studies have yet to be published in peer-reviewed journals.
“A lot of the tests that came back in China that you read about, where it looks like people were reinfected, those look extremely likely to be the result of testing errors,” Bharti said. “If you’re testing a lot of people like they did in China, you’re likely to get a lot of false positives and a lot of false negatives.”
The scientists searching for a vaccine against the coronavirus are trying to come up with a tool that will prime the body’s immune system to identify and attack viral particles before they are able to infect a person’s cells.
In the case of a vaccine against the Ebola virus that has been deployed to fight an outbreak in Congo, scientists manipulated a different virus that is known to be harmless to humans. They replaced a protein in that virus with one found on the surface of an Ebola virus particle. When injected into humans, the immune system would learn to recognize the protein found on an Ebola virus particle as an invader, priming the body to recognize and stop the Ebola virus if a person were infected.
The way a vaccine is structured can determine just how long it conveys immunity. A vaccine developed long ago to combat the measles virus targets a part of the virus that does not mutate, meaning the vaccine still works decades after it was first introduced.
But vaccines against the seasonal flu virus target two particular proteins on the virus’s surface — in shorthand, the H and the N — and those particles mutate frequently. One season might be dominated by an H1N1 strain of the virus, while the next might see a wider spread of H3N2. Because those proteins mutate regularly, doctors urge people to get their flu shots yearly to keep their immune system primed.
What is known so far about the coronavirus appears to show it is relatively stable, and that it has yet to mutate in significant ways, even though it has infected more than 3 million people across the globe. That, Osterholm said, should give vaccine researchers the chance to develop something that conveys more immunity than the relatively temporary flu shot.
“The virus isn’t changing in a fundamental way that should make it immunologically different a year from now,” he said. “We hope this is going to be more akin to a measles vaccine.”
The dozens of laboratories across the world racing to find a vaccine face serious and necessary hurdles before they can bring a product to market, to ensure that the final product does not do more harm than good. Those barriers are higher than potential treatments for the virus would be; the treatments are aimed at making a sick person better, while the vaccine is meant to expose the body to a new pathogen.
“You are putting people in danger who may never be challenged by this virus. So there’s a very low threshold for vaccine failure,” Bharti said. “The odds are pretty low for any single candidate” to win approval.
That fact, Bharti said, is what strikes many scientists as so bizarre about vaccine skeptics and anti-vaccination activists who do not want to vaccinate their children. The high hurdles that well-made vaccines have overcome, she said, make them “by far the safest medical intervention out there.”