When Jonathan Isaac, a basketball player for the Orlando Magic team, explained why he had chosen not to be vaccinated against the coronavirus, he connected with a controversy that has been heating up for months: People who have had COVID-19 (which according to Isaac is his case) do they really need the vaccine?
That question has propelled devious immunity concepts into a national debate on vaccine enforcement in which politicians, athletes, law professors, and psychiatrists have weighed in on the relative strength of so-called natural immunity against the protection afforded by vaccines.
But the answer, like almost everything related to the virus, is complicated.
While many people who have recovered from COVID-19 can emerge relatively unscathed from a second encounter with the virus, the strength and durability of their immunity depends on their age, health, and severity of the initial infection.
“That’s the natural infection thing: you could be on the very low end or the very high end, depending on the type of disease you developed,” said Akiko Iwasaki, an immunologist at Yale University.
Those with strong natural immunity could be protected from re-infection for up to a year. But according to experts, even they shouldn’t ignore the vaccine. For starters, boosting their immunity with a vaccine will most likely provide lasting protection against all variants.
“If you got the infection and then got vaccinated, you have superpowers,” said Jennifer Gommerman, an immunologist at the University of Toronto.
Without the vaccine booster, the antibodies to an infection will fade, leaving people recovered from COVID-19 vulnerable to reinfection and mild illness caused by the variants, and perhaps susceptible to transmitting the virus to others.
This is the same argument for giving booster doses to people on the full vaccination schedule, said Michel Nussenzweig, an immunologist at Rockefeller University in New York. “After a certain period of time either you will receive a reinforcement or you will become infected,” he said.
It is difficult to analyze the comparison between the immunity granted by infection and that obtained by vaccination. Dozens of studies have deepened the debate and reached contradictory conclusions.
Some consistent patterns have emerged: Two doses of an mRNA vaccine produce more antibodies, and more reliably, than one coronavirus infection. But antibodies from a previous infection are more diverse than those produced by vaccines, so they are able to defend against a wider range of variants.
Studies promoting the durability and strength of natural immunity are hampered by a crucial flaw. By definition, they only assess the responses of people who survived COVID-19. The path to natural immunity is dangerous and uncertain, Nussenzweig said.
For starters, only 85 to 90 percent of people who test positive for the virus and recover have detectable antibodies. The strength and durability of the response varies.
For example, while immunity gained from vaccines and infection is comparable among younger people, two doses of mRNA vaccines protected adults 65 and older better than a previous infection.
Research published in May by Iwasaki’s team showed a gradual increase in the level of antibodies as the severity of the infection increased. About 43 percent of the recovered people had no detectable neutralizing antibodies – the kind needed to prevent reinfection – according to one study. Antibodies fell to undetectable levels after about two months in about 30 percent of the people who recovered.
Other researchers might find different results depending on the severity of the disease in the participants, said Fikadu Tafesse, an immunologist at Oregon Health and Science University.
“If your tested group consists only of hospitalized individuals, I think the probability of getting detectable antibodies will be higher,” said Tafesse.
In terms of the quality of the antibodies, it makes sense that invasion by a live virus produces a broader immune response than injection of the single protein encoded in vaccines would, he and others said.
The virus usually stimulates defenses in the nose and throat – exactly where they are needed to prevent a second infection – while vaccines produce antibodies mainly in the blood.
“That will give you an advantage in terms of resistance to further infection,” Gommerman said.
Fragments of the virus could also remain in the body for weeks after infection, giving the immune system more time to learn how to fight it, while the proteins carried by the vaccine quickly leave the body.
Several studies have already shown that reinfections, at least with the first versions of the virus, are not common.
At the Cleveland Clinic, none of the 1,359 healthcare workers who didn’t get vaccinated after having COVID-19 tested positive for the virus for many months, said Nabin Shrestha, the clinic’s infectious disease physician.
However, he acknowledged that the findings should be interpreted with caution. The clinic examined only people who were visibly ill, so they may have missed reinfections that produced no symptoms. The participants were on average 39 years old, so the results may not apply to older adults, who may be more likely to get infected again.
Also, most studies have followed people for only a year or so, Shrestha noted. “The important question is: ‘How long will it provide protection?’ Because we know it will not be for life,” he said.
The efficacy of immunity against the newer variants is also unclear. Most of the studies were completed before the delta variant became dominant, and the most recent investigations show irregularities.
The most cited study in favor of the potency of natural immunity against the delta variant comes from Israel.
The study found that post-vaccination infections were 13 times more likely than reinfections in unvaccinated people, and symptomatic post-vaccination infections were 27 times more likely to occur than symptomatic reinfections.
For those lucky enough to have recovered from COVID-19, the vaccine remains the ideal option, according to experts. It provides a significant increase in antibody levels and a nearly impenetrable immune shield, possibly even against future variants.
“They are like rock stars in the face of all variations,” said Duane Wesemann, an immunologist at Harvard University School of Medicine.
The colorful graphics in Wesemann’s recent article have been helpful in convincing recovered COVID-19 patients of the great advantage that even a single dose could offer them, he said.
Regardless of the changing understanding of natural immunity, there is a point where there is almost universal consensus among scientists: For people who have never been infected, vaccines are much safer and much less risky than COVID-19.
Many people who argue against vaccines cite the low death rates from COVID-19 among young people. But even seemingly mild cases of COVID-19 can cause long-term damage to the heart, kidneys and brain, or leave people feeling tired and unwell for weeks or months, Iwasaki warned.
“No one should try to acquire immunity through natural infection,” he said. “It is too dangerous.”