The speed at which the United States reaches herd immunity from the coronavirus will depend on the lasting effect of natural immunity.
Herd immunity happens when enough people become immune due to vaccination or natural immunity. Natural immunity occurs when a person is infected with the coronavirus, and his immune system produces antibodies that will fight off future infections.
Early research has suggested that the natural immunity from coronavirus infection only lasted a few months, while more recent research suggests that it may be longer-lasting.
Sen. Rand Paul, a Kentucky Republican, has refused to get a COVID-19 vaccine because he has natural immunity. Paul, who was infected with the virus in March 2020 but had no symptoms, wrote recently in an editorial that “Vaccines are a replacement for natural immunity. They aren’t necessarily better.”
But Susan Hassig, an epidemiology professor at Tulane University School of Public Health and Tropical Medicine, disagrees.
US MOVES TOWARD CORONAVIRUS HERD IMMUNITY
“The challenge with the natural component, in terms of protecting, is that we have a very heterogeneous response to natural infection, especially since so many people are mildly affected by the virus,” Hassig said. “Individuals who get really sick tend to have a much more robust and complete immune response, more similar to a vaccination, than individuals who are mildly affected and have a shorter duration with the virus.”
In June last year, Nature Medicine published research examining COVID-19 patients in China and found that 40% of patients who were asymptomatic were no longer producing antibodies versus 13% of those who were seriously ill. A research letter published a few months later in the New England Journal of Medicine also found a rapid decay of antibodies in people who had a mild case of COVID-19. Research on healthcare workers who had mild COVID-19 found that, in two months, antibodies had declined in 94% of them while 28% had no antibodies at all.
Other research that did not distinguish between patients with mild or severe cases of COVID-19 also found drops in immunity. A study of British patients found that people testing positive with coronavirus antibodies had fallen by more than one-quarter from June to September 2020.
Most experts say that 80% of the U.S. population must be immune to achieve herd immunity nationwide. Relying solely on vaccination to ensure that we get there will involve a long wait. Currently, only about 40% of the population is fully vaccinated. At the current rate, it will take at least until November to reach 80%, assuming vaccination rates don’t slow further.
A rough yet conservative estimate by the Washington Examiner suggests that natural immunity combined with those who are fully vaccinated would mean that 55% of the population is immune to the coronavirus. But that will depend on how long natural immunity lasts.
The good news is that more recent research suggests it may last longer than previously thought.
In December, a study that examined more than 30,000 patients in New York with mild-to-moderate COVID-19 found that 90% still had antibodies after five months. A study in Science magazine found that both B Cells and T Cells that are crucial in fighting off coronavirus infections lasted at least six months in 95% of COVID-19 patients.
Two studies that appeared in May are even more promising. In the first, a study of 63 COVID-19 patients found that in those who had not been vaccinated, the amount of B Cells were stable at six to 12 months. A study published in Nature found that the B Cells persist in the bone marrow of patients with COVID-19 for up to almost a year. It is the B Cells that will churn out antibodies to attack the coronavirus should it infect a person a second time.
“The papers are consistent with the growing body of literature that suggests that immunity elicited by infection and vaccination for SARS-CoV-2 appears to be long-lived,” said Scott Hensley, an immunologist at the University of Pennsylvania, told the New York Times. Hensley was not involved in the research.
However, there was one warning to come out of the recent Nature study. Of the 19 patients whose bone marrow was examined, four did not have any B Cells.
“It tells me that even if you got infected, it doesn’t mean that you have a super immune response,” Ali Ellebedy, an immunologist at Washington University in St. Louis and the lead researcher on the study, told the New York Times.
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That means that people who have been infected should consider getting a vaccine, even possibly Paul.
