Americans are weary of the pandemic and ready to get back a world without masks and social distancing. To make that happen, we need a good path to immunity against COVID-19. According to Vineet Menachery, a coronavirus researcher at the University of Texas Medical Branch in Galveston, this could play out in one of four different ways: through sterilizing immunity, functional immunity, waning immunity or lost immunity.
One possible path is sterilizing immunity. In this case, the body is able to fight off the new coronavirus before it takes hold, following a path set by diseases like measles and mumps, which humans generally get only once. But sterilizing immunity rarely happens with respiratory viruses such as SARS-CoV-2. What’s worse, if the body can’t create sterilizing immunity in response to an infection with the disease, it’s less likely that a vaccine will, either.
According to Malik Peiris, a coronavirus expert at Hong Kong University, in tests with monkeys, most of the experimental vaccines against SARS-CoV-1 have protected the lungs from severe disease but can’t stop the virus from replicating in the upper airways. (Peiris was one of the discoverers of SARS-1.) This suggests that a COVID-19 vaccine might be better for keeping people out of the intensive care unit than for preventing spread of the disease.
A second type of immunity is functional immunity. In this scenario, those who either have been infected with the virus or inoculated against it could get it again. But when they do, the body’s immune system would kick in and keep the infection from becoming too severe. According to Menachery, this is probably the most likely scenario with COVID-19.
Researchers have worried about how lasting the body’s immune response will be after infection with COVID-19. Some studies have found that the immune response is weak or doesn’t last long. Scientists caution that even once a vaccine is approved, it will take at least two doses to confer enough immunity. However, even the Hong Kong man known to have been reinfected with SARS-CoV-2 didn’t show symptoms of illness the second time around.
Angela Rasmussen, a virologist at Columbia University in New York, notes that while the evidence supports functional immunity, it’s going to take time to see how long immune responses to the virus will last. Menachery says that even after antibodies wane, the body has “memory responses” to the virus (and thus should be better equipped to fight off the virus in reinfections).
According to Christian Drosten, director of the Institute of Virology at Berlin’s Charité University Hospital and another discoverer of SARS-1, it’s possible that most of those who get COVID-19 will end up with a functional immunity than rivals the power of a sterilizing immunity. While people may be able to get reinfected, they won’t suffer serious illness and the virus won’t replicate as much with subsequent infections. Less virus replication means less chance these asymptomatic carriers will pass the disease to others.
In this scenario, children, who tend to get less severe versions of the virus, might get the virus first at a young age and then have it repeatedly into adulthood with few or no unwanted effects. Florian Krammer, a professor of vaccinology at the Icahn School of Medicine at Mount Sinai Hospital, New York, thinks that a vaccine will speed up this process, so that a greater proportion of the population ends up getting exposure to the disease, but with fewer and fewer ill effects.
While this scenario is both likely and is cause for hope, there’s one caveat. People who either do not live in an area where they are exposed to the virus or who do not get a vaccine may later end up with a severe version of the illness once exposed, according to Stanley Perlman, a coronavirus researcher at the University of Iowa.
A third scenario is that of waning infection, in which people who have been infected or who were vaccinated lose immunity as time passes. But Menachery thinks that even if this happens, subsequent infections won’t be as severe. Infections with the four coronaviruses that cause roughly 15% of all common colds tend to follow this pattern: those who get the virus once can get it again relatively quickly.
However, one British study found that in people reinfected with one of those cold-causing coronaviruses, the period of viral shedding was so short that none of people who were reinfected got cold symptoms. A decades-long Dutch study of four different coronaviruses found that its study patients were infected multiple times with the each of the viruses, frequently at about 12 months after the previous infection. Senior author Lia van der Hoek of Amsterdam University Medical Center thinks waning immunity is the most likely scenario for SARS-CoV-2, but adds that scientists can’t fully predict what symptoms will happen when reinfection occurs.
The fourth scenario is lost immunity, wherein infected people completely lose immunity so that any reinfection will be just like a first infection, with all the same risks of getting a severe version of the disease. Some scientists believe this is the least likely scenario. However, Menachery thinks even if this scenario proves false for some of the population, it’s still possible that people who only had a mild infection the first time and whose bodies did not generate a great enough immune response could get a worse version of the illness on reinfection.
So how quickly can we step away from the COVID-19 precautions, if one of the better scenarios appears to be correct? It could be a while, according to Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center, Boston. The virus is new, and most people in the world have not had it yet. Even once we get a viable vaccine, inoculating a sizable enough proportion of the population could take years.
Disclaimer: This article does not provide medical advice. Do not take action based solely on this article and always consult with an appropriate healthcare professional. This article is purely for informational purposes.