Along with hopes of developing an effective vaccine, a long-term goal in the fight against COVID-19 has been achieving widespread immunity. The following presents three potential immunity scenarios laid out by health experts, from the best case to the worst.
Throughout the pandemic, the World Health Organization has cautioned people who have recovered from COVID-19 that there is no evidence they are immune from reinfection. Recent studies indicate that protective antibodies may fade in a matter of months, which could leave some people susceptible to contracting the disease more than once, or in seasonal waves, similar to catching the other strains of coronaviruses that can cause the common cold.
On August 24, researchers at the University of Hong Kong announced they had found evidence that individuals can be reinfected with SARS-CoV-2, the virus that causes COVID-19. The team said a 33-year-old man from the region had tested positive for the second time in four and a half months, suggesting the concept of herd immunity could be unlikely, and a hypothetical vaccine that scientists are working to develop might not protect the global population that awaits for extended periods of time.
STAT News recently interviewed several health experts about ways the world can coexist with COVID-19. Vineet Menachery, a coronavirus researcher at the University of Texas Medical Branch in Galveston, presented four possible immunity scenarios, one of which is a subset of another, based on the human body’s response to other coronavirus types. The outlet described the potential outcomes as “hopeful,” but emphasized that Dr. Menachery’s general categorizations “are educated guesses” which “cover a spectrum, and the lines between some of the scenarios can be blurry in spots.”
Will Covid-19 vaccines be protective and long-lasting? Will our immune systems learn — and remember — how to cope with the new threat? https://t.co/JfhzirCtHS
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Below are three potential scenarios, drawing heavily from Dr. Menachery’s theories and other experts STAT consulted as well as additional sources.
1. Complete immunity — best-case scenario, but “not so likely”
Sterilizing immunity, which essentially means humans would be resistant to reinfection, is a best-case scenario. Protection would persist because the human body’s forms of immunity response minimize the ramifications of repeat infection. For example, the antibodies generated by a measles infection generally last a lifetime.
Chia-Yi Hou, a health writer for The Hill, explains:
Sterilizing immunity means that the immune system is able to stop a pathogen, including viruses, from replicating within your body.
This typically happens when immune cells in the body are able to bind to the pathogen in places that prevent it from being able to enter a cell where it can start making copies of itself. Some of these immune cells may produce sterilizing antibodies, which are proteins that recognize specific proteins and structures on the surfaces of pathogens.
To achieve sterilizing immunity, your body needs to produce enough neutralizing antibodies and it needs to be able to do so in the long term. Ideally, it leads to life-long immunity.
Marion Koopmans, head of virology at Erasmus Medical Center in the Netherlands, told STAT that sterilizing immunity “is out of the question, as with any respiratory virus.” Another expert interviewed described the option as “not so likely.”
As STAT reported, “viruses that infect via the mucus membranes of the nose and throat, like SARS-2, typically don’t induce sterilizing immunity.”
Health experts said experimental COVID-19 vaccines tested on primates do not block replication of the virus in the upper respiratory tract, which includes the nose, nasal passages, and sinuses.
2. Partial immunity — most likely scenario
Dr. Menachery envisions a concept he calls “functional immunity,” effectively partial immunity, as the most likely outcome. Even though the number of antibody proteins in the blood may significantly drop after an infection is cleared, the human body stores “memory cells” that could detect and fight off those same viruses at a later date.
“The idea there is that, yes, your antibodies might wane, but your memory responses aren’t absent,” Menachery said. More from STAT:
Under this scenario, people whose immune systems have been primed to recognize and fight the virus — whether through infection or vaccination — could contract it again in the future. But these infections would be cut short as the immune system’s defenses kick into gear. People infected might not develop symptoms or might have a mild, cold-like infection…
STAT cites “enormous amounts of debate” about the ability of people to produce a “durable” or long-lasting immune response to the virus, but says that experts told the outlet that so far immune responses to the virus follow standard patterns.
Some scientists believe rapidly fading antibody levels could pose a challenge to vaccine developers. Several suggested the companies consider booster vaccinations that would be administered at regular intervals, especially for the most vulnerable groups.
A recent King’s College London study found that COVID-19 patients with the most severe symptoms produced the highest antibody levels to fight the infection. Another research group from Chongqing Medical University in China provided data that suggests asymptomatic people had a weaker immune response to the virus.
A variant of this functional immunity, Menachery suggests, is “waning immunity,” in which individuals might eventually become reinfected, but the new infection would result in less severe symptoms than the previous episode. “You will never get as sick as you were the first time,” Dr. Menachery explained.
“This is a pattern seen with the four coronaviruses that cause about 15% of what we consider common colds – OC43, 229E, NL63, and HKU1,” according to STAT. “People can be reinfected with these viruses after a relatively short period of time.”
3. Fully lost immunity — worst-case scenario, probably “off the table”
Dr. Menachery described the worst possible outcome as “lost immunity,” meaning immunity would completely fade out, leaving people vulnerable to catch the virus again with unpredictable symptoms that may be just as severe as previous bouts with the disease.
“A reinfection after that point would be like a first infection — carrying all the same risk of severe disease now seen with Covid-19,” STAT explains. “Lost immunity describes a scenario in which people who have been infected would lose all their immune munitions against the virus within some time frame.”
However, STAT says none of the experts with whom they had consulted thought it was a real possibility. If these experts are right, says the health news outlet, we can expect the threat of the virus to wane, with the virus eventually becoming “the fifth human coronavirus to cause common colds.”
Related: How Effective Is Mask Wearing? Here’s What The Science Suggests.