“If your cohort is just only hospitalized individuals, I think the chance of having a detectable antibody is higher,” Dr. Tafesse said.
In terms of the quality of the antibodies, it makes sense that invasion by a live virus would produce a broader immune response than would injecting the single protein encoded in the vaccines, he and others said.
The virus would stimulate defenses in the nose and throat — exactly where they are needed to prevent a second infection — while the vaccines produce antibodies mainly in the blood.
“That will give you an edge in terms of resisting a subsequent infection,” Dr. Gommerman said.
Fragments of the virus may also persist in the body for weeks after infection, which gives the immune system more time to learn to fight it, while the proteins carried by the vaccine quickly exit the body.
Several studies have now shown that reinfections, at least with the earlier versions of the virus, are rare.
At the Cleveland Clinic, none of 1,359 health care workers who remained unvaccinated after having Covid-19 tested positive for the virus over many months, noted Dr. Nabin Shrestha, an infectious disease physician at the clinic.
But the findings must be interpreted with caution, he acknowledged. The clinic tested only people who were visibly ill, and may have missed reinfections that did not produce symptoms. The participants were 39 years old on average, so the results may not apply to older adults, who would be more likely to become infected again.