• Is ‘natural immunity’ better than a vaccine? Experts say no,

On the heels of last month’s news of stunning results from Pfizer’s and Moderna’s experimental COVID19 vaccines, Sen. Rand Paul tweeted a provocative comparison.

The new vaccines were 90% and 94.5% effective, Mr. Paul said. But “naturally acquired” COVID-19 immunity was even better, at 99.9982%, he claimed.

Mr. Paul, R-Ky., is one of many people who, weary of lockdowns and economic losses, have extolled the benefits of contracting the coronavirus. The senator was diagnosed with the disease this year, and since then, he has argued from his experience that surviving a bout of COVID-19 confers greater protection and poses fewer risks than getting vaccinated.

The trouble with that logic is that it’s difficult to predict who will survive an infection unscathed, said Jennifer Gommerman, an immunologist at the University of Toronto. Given all of the unknowns — like a region’s hospital capacity, or the strength of a person’s immune response — choosing the disease over the vaccine is “a very bad decision,” she said.

The primary advantage of a vaccine is that it’s predictable and safe, Ms. Gommerman said. “It’s been optimally tailored to generate an effective immune response.”

While COVID-19 vaccines have predictably prevented illness, and they are a far safer bet, experts said.

Vaccines for some pathogens, like pneumococcal bacteria, induce better immunity than the natural infection does. Early evidence suggests that the COVID-19 vaccines may fall into this category. Volunteers who received the Moderna shot had more antibodies — one marker of immune response — in their blood than did people who had been sick with COVID-19.

In other cases, however, a natural infection is more powerful than a vaccine. For example, having mumps — which can cause sterility in men — generates lifelong immunity, but some people who have received one or two doses of the vaccine still get the disease.

To Mr. Paul’s point: Natural immunity from the coronavirus is fortunately quite strong. A vast majority of people infected produce at least some antibodies and immune cells that can fight off the infection.

In people who are only mildly ill, the immune protection that can prevent a second infection may wane within a few months. “Those people might benefit more from the vaccine than others would,” said Bill Hanage, an epidemiologist at the Harvard T.H. ChanSchool of Public Health.