Last week, Sen. Rand Paul (R-Ky.) posted a Twitter thread asserting that people who have survived a covid-19 infection were unlikely to be reinfected and have better immunity against variants than those who have been vaccinated against — but not infected by — SARS-CoV-2, the virus that causes covid.
The social media communication represented his latest salvo in the ongoing debate over whether natural immunity is equivalent or even better than vaccination.
While the science on the subject is still evolving, a look at the evidence behind Paul's series of tweets seemed in order. After all, though almost 65% of Americans have received at least one dose of a covid vaccine, some people who have recovered from covid may not feel a need to get shot. Paul, who was the first senator to be diagnosed with the virus, is among them. Here's a deeper look at what Paul said on Twitter, the studies he cited and how researchers characterized his comments.
Breaking Down the Twitter Thread
In his first tweet, Paul referenced a recent Cleveland Clinic study finding that among subjects who were unvaccinated but had already had covid-19, there were no re-infections in a five-month observation period: "Great news! Cleveland clinic study of 52,238 employees shows unvaccinated people who have had COVID 19 have no difference in re-infection rate than people who had COVID 19 and who took the vaccine."
In subsequent tweets, the senator said: "The immune response to natural infection is highly likely to provide protective immunity even against the SARS-CoV-2 variants. … Thus, recovered COVID-19 patients are likely to better defend against the variants than persons who have not been infected but have been immunized with spike-containing vaccines only." All three vaccines authorized for emergency use in the U.S. (Pfizer-BioNTech, Moderna and Johnson & Johnson) contain genetic instructions that tell our cells how to make a spike protein associated with the coronavirus. The presence of that spike protein then causes our bodies to make antibodies to protect against covid.
At the end of his final tweet, Rand then linked to a second study led by scientists at the Fred Hutchinson Cancer Research Center in Seattle to support his assertions.
Digesting the Scientific Papers
Paul referenced two scientific papers in his tweet thread — both of which are preprints, meaning they have not yet been published in scientific journals or been peer-reviewed.
One was a study from the Cleveland Clinic following four categories of health care workers: unvaccinated but previously infected; unvaccinated but not previously infected; vaccinated and previously infected; and vaccinated but not previously infected. The workers were followed for five months.
The researchers found that no one who was unvaccinated but had previously been infected with covid became infected again during the five-month study period. Infections were almost zero among those who were vaccinated, while there was a steady increase in infections among those who were unvaccinated and previously uninfected.
When asked whether he believed Paul's tweet had interpreted his study results correctly, the study's lead author, Dr. Nabin Shrestha, an infectious diseases specialist at Cleveland Clinic, said "it was an accurate interpretation of the study's findings."
However, Dr. George Rutherford, an epidemiologist at the University of California-San Francisco, wrote in an email that he would add one caveat to the wording of Paul's tweet: "Note that in his tweet Senator Paul seems to suggest that the denominator of previously infected health care workers at the Cleveland Clinic was 52,238 — that was the total number in the whole study. There were 1,359 that were previously infected and never vaccinated, and there were no reinfections noted over a median follow up of 143 days. So, the tweet itself is accurate if read literally but the denominator is really 1,359."
As for the other study Paul mentioned, researchers analyzed covid-19 immunity in those who had been infected with the covid virus and those who hadn't and found that infection activated a range of immune cells and immunity lasted at least eight months.
In his last two tweets in the thread, Paul quotes directly from the study's "discussion" section: "The immune response to natural infection is highly likely to provide protective immunity even against the SARS-CoV-2 variants. … Thus, recovered COVID-19 patients are likely to better defend against the variants than persons who have not been infected but have been immunized with spike-containing vaccines only."
The lead study author, Kristen Cohen, a senior staff scientist in the Vaccine and Infectious Disease Division at the Fred Hutchinson Cancer Research Center in Seattle, acknowledged that Paul's tweet was a direct quote from the study. Still, she said, in her view, the quote was taken out of context and presented to suit Paul's objective — but does not accurately reflect the overall take-home message from the study's findings.
That's because, she said, Paul was quoting from the discussion section of the paper. The discussion is the final section of a scientific paper, and Cohen said its purpose here was to project what the study's findings could imply for a broader scientific significance.
"We wrote that recovering covid patients are "likely" to better defend against variants than those who have just been immunized, but it's not saying they do," said Cohen. "It's not saying they have been known to. It's making a hypothesis or basically saying this could be the case."
In fact, Cohen's study did not include any subjects who had been vaccinated. The researchers were merely reasoning in the sentence Paul quoted that, based on the data showing the immune system's broad natural response, those who recover from covid-19 and then receive a vaccine may be better protected against covid variants than those who had only vaccine-induced immunity.
"We did not intend to argue that infected people do not need to get vaccinated or that their immune responses are superior," Cohen wrote in an email.
However, Cohen recognized the sentence was confusing when taken out of context and said she will eliminate it from the paper when it gets submitted for publication.
Cohen pointed us to another Fred Hutchinson-led study with which she was involved. It did show that people who previously had covid-19 benefited from also getting vaccinated, because there was a significant boost in immune response, especially against variants.
The Conventional Wisdom on Natural Immunity
So, what's known from these two studies is that surviving a covid infection confers a significant amount of immunity against the virus. Other studies also support this assertion.
"Existing literature does show natural immunity provides protection against COVID-19," said Shane Crotty, a professor at the Center for Infectious Disease and Vaccine Research at the La Jolla Institute for Immunology who has published numerous peer-reviewed studies on natural immunity against covid-19. He said such immunity particularly protects against hospitalizations and severe illness.
In Crotty's own recent study, the largest yet to measure the molecules and cells involved in immune protection, his team found that natural immunity against covid lasted at least eight months. Based on projections, it could last up to a couple of years.
While that is good news, Crotty said, there are three points of caution.
First, though natural immunity appears to be very effective against the current dominant U.S. variant (known as alpha), it also appears weaker than vaccine immunity against some of the variants circulating, such as the delta variant, first detected in India. That means if those variants eventually become dominant in the U.S., people relying on natural immunity would be less protected than those who are vaccinated.
Second, there is a lack of data about whether natural immunity prevents asymptomatic transmission and infection. Several other studies, though, show vaccines do.
Third, Crotty said his studies have shown that levels of natural immunity can vary widely in individuals. His team even found a hundredfold difference in the number of immune cells among people.
"If you thought about the immune system as a basketball game and you thought about that as a team scoring 1 point, and another team scoring 100 points, that's a big difference," said Crotty. "We're not so confident that people at the low end of immunity levels would be as protected against covid-19."
But those who receive a vaccine shot have a much more consistent number of immune cells, since everyone receives the same dose amount, said Crotty.
With all that in mind, the Centers for Disease Control and Prevention recommends that those who previously had covid-19 should get vaccinated and receive both doses of a vaccine, whether it's the Pfizer-BioNTech or Moderna vaccine. Fauci, the nation's leading infectious disease expert, reiterated this message during a White House covid-19 briefing last month.