While much of the recent discussion about COVID-19 has focused on vaccinated vs. unvaccinated persons, there’s been less talk about those who have acquired natural immunity through infection by the virus.
It does appear that previous infection of SARS-CoV-2, the virus that causes COVID-19, offers some immunity to reinfection, although there’s ongoing debate over how much and for how long.
Natural immunity “does provide pretty good protection, there’s no doubt about that,” said Dr. Liam Sullivan, a Grand Rapids infectious disease specialist with Spectrum Health. “The question is how long does that protection last, and I think it’s too early to say.”
Still, medical experts highly encourage people who have had COVID-19 to get vaccinated, saying there is little downside and growing evidence that it protects against recurrent bouts of the virus.
Below is a look at the latest research on natural immunity virus.
An estimated 28% of Michigan residents have COVID-19 antibodies that indicate previous infection.
That’s based on the results of 1,352 antigen tests taken in Michigan during the last two weeks of July, according to the federal Centers for Disease Control.
The July estimate that 28.1% of Michigan’s population has antibodies is up from 18.9% at the end of February 2021, just before Michigan’s spring surge.
Based on the July 2021 antigen results, the CDC estimates that 34% of Michigan residents under 18 have been infected by the virus so far; 31% of those age 18 to 49; 24% age 50 to 64, and 17% of those age 65 and older.
The latest data means an estimated 2.8 million Michiganders have contracted the virus to date, about three times the number of confirmed cases.
Natural infection seems strong against Delta variant.
A new study from Israel suggests natural immunity can be more protective of against the Delta variant than two doses of the Pfizer vaccine. The study compared 16,125 Israelis who were vaccinated in January or February to 16,125 infected with SARS-CoV-2 during that time, and looked at the number of breakthrough cases and reinfections from June 1 to Aug. 14.
The study found 238 breakthrough cases, or 1.5% of the vaccinated group. Meanwhile, among the unvaccinated persons, there were 19 reinfections or 0.12% of the group.
The Israeli study also looked at unvaccinated persons infected in 2020 and found a higher reinfection rate than those infected more recently, but the reinfection rate was still below the rate of breakthrough cases for vaccinated persons.
Earlier this summer, the Cleveland Clinic released a study of its employees, which found no reinfections among unvaccinated workers who were previously infected with SARS-CoV-2. That study concluded that previous infection appeared to offer similar protection to vaccination.
But that immunity can considerably vary by strain.
While the Israeli study indicates that infection by the original strain seems to protect against Delta, which originated in India, there have been more reinfections associated with strains originating out of South Africa and Brazil.
In the P.1 strain originating in Brazil, one study found antibody effectiveness six times weaker against the P.1 in comparison with the original SARS-CoV-2 strains. That study estimated that 25% to 61% of previously infected patients were susceptible to P.1 infection.
Similar issues have been found with the South African variant, also known as B.1.351. A vaccine trial for Novavax found that participants in the control group who were previously infected were just as likely to become ill with B.1.351 as those without natural antibodies, suggesting older strains of COVID-19 failed to provide immunity against B.1.351. By comparison, the vaccine did offer some protection.
Vaccines seem to be more consistent in dealing with mutant strains.
There are some important differences in immunity acquired via an mRNA vaccine vs. natural immunity that suggest vaccines may provide more consistent protection against the various mutations of COVID-19, according to a study released in June by the National Institute of Health.
The study looked specifically at on the receptor binding domain (RBD), a key region of the spike protein on the outer surface of SARS-CoV-2. It found “antibodies generated by the mRNA vaccine were more focused to the RBD compared to antibodies elicited by an infection, which more often targeted other portions of the spike protein. Importantly, the vaccine-elicited antibodies targeted a broader range of places on the RBD than those elicited by natural infection,” the NIH said.
“These findings suggest that natural immunity and vaccine-generated immunity to SARS-CoV-2 will differ in how they recognize new viral variants. What’s more, antibodies acquired with the help of a vaccine may be more likely to target new SARS-CoV-2 variants potently, even when the variants carry new mutations in the RBD,” the NIH said.
Reinfections are more common among people age 65 and older.
While reinfections are rare, they are more common in senior citizens, according to a Danish study released in March 2021.
The study looked at 4 million Danes infected by the virus to calculate reinfection rates. Senior citizens appeared to have about 47% protection against repeat infection, compared to younger people who seemed to have about 80% protection from reinfection, study found.
And a study in a Kentucky nursing home found that reinfections in older people tend to be more severe than the first bout of the illness.
That’s been his experience, said said Dr. Michael Zaroukian, a Lansing-area family physician who specializes in immunology.
“When people get sick a second time, we’re seeing them in the hospital, not just seeing them in the office,” he said.
The strength of natural immunity can vary between individuals.
Prior exposure to SARS-CoV-2 does not guarantee a high level of antibodies, nor does it guarantee a robust antibody response to the first vaccine dose, according to a new study out of Northwestern University in Chicago.
That study found people with mild or asymptomatic cases of COVID-19 had a lower antibody response that those with more serious symptoms.
“Many people, and many doctors, are assuming that any prior exposure to SARS-CoV-2 will confer immunity to re-infection. Based on this logic, some people with prior exposure don’t think they need to get vaccinated. Or if they do get vaccinated, they think that they only need the first dose of the two-dose Pfizer/Moderna vaccines,” Thomas McCade, a biological anthropologist who was part of the team that conducted the study, said in a press release accompanying the study’s release.
“Our study shows that prior exposure to SARS-CoV-2 does not guarantee a high level of antibodies, nor does it guarantee a robust antibody response to the first vaccine dose. For people who had mild or asymptomatic infections, their antibody response to vaccination is essentially the same as it is for people who have not been previously exposed.”
Vaccination offers additional protection to people with natural immunity
Unvaccinated people previously infected with SARS-CoV-2 were more than twice as likely to get reinfected compared to previously infected people who were inoculated, according to a recent study out of Kentucky.
A similar outcome was reported in the Israeli study, which also compared unvaccinated individuals were previously infected to those who were previously infected and obtained the vaccine. “The latter group had a significant decreased risk of reinfection,” the study said.
Colorado fitness coach Bill Phillips has been an outspoken advocate for vaccination after infection after he spent two months in the hospital during his second bout with COVID-19.
Phillips, 56, decided not to get vaccinated, figuring he was in top physical condition and had antibodies that indicated a previous infection. But he caught COVID-19 again in June, ended up on a ventilator and almost died. He recently left the hospital, and is in rehab, and a wheelchair and supplemental oxygen.
“It didn’t help that I could bench press 300 pounds or run a mile straight up a hill,” Phillips told KUSA-TV in Denver. “I made a mistake. That mistake came that close to costing me my life.”
Doctors warn against trying to deliberately acquire natural immunity
Even though natural immunity can offer at least protection against reinfection of SARS-CoV-2, doctors say it’s a very bad idea for people to deliberately expose themselves to the virus.
“It’s like Russian Roulette. You don’t want to roll the dice,” said Dr. Mark Hamed, health department medical director for Huron, Lapeer, Sanilac, Tuscola, Alcona, Iosco, Ogemaw and Oscoda counties.
Since the start of the pandemic, almost 2% of Americans with confirmed COVID-19 have died, 7% have been hospitalized and 10% to 30% experience “long COVID,” which are lingering symptoms such as extreme fatigue, respiratory issues, headaches, brain fog and organ damage that last weeks or months beyond the initial infection.
The “Russian roulette” factor also is true with children, even though younger people are much less likely to have a serious case of COVID, said Dr. Rosemary Olivero, a pediatric infectious disease specialist with Spectrum Health in Grand Rapids.
“We don’t quite know yet if the natural immunity or the vaccine-generated immunity is superior over the long term,” she said. “Those studies are ongoing and we’re looking for that data constantly so I can’t really give you a perfect estimate of that.
“However, because the adverse effects of having a vaccine are so extremely low, and the risk of having a negative consequence of COVID-19 probably ranges anywhere from 3% to 10% for a child, I do think that vaccination is the safer way to get a population immune to the virus,” she said.
After the Israel study came out indicating that natural immunity provides strong protection against reinfection of the Delta virus, scientists said they don’t want to send the wrong message to the public.
“What we don’t want people to say is: ‘All right, I should go out and get infected, I should have an infection party,’” Michel Nussenzweig, an immunologist at Rockefeller University in New York, told Science magazine. “Because somebody could die.”
Read more on MLive:
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Adolescents see small, but greatest increase in COVID-19 vaccinations in last 3 weeks
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