More than a year after the start of the COVID-19 pandemic, many questions remain about immunity against previous infections and vaccinations.
For example, how long can the immunity last? Do people need to be fully vaccinated if they have already been infected with COVID-19? Do mild and severe infections differ in antibody buildup and levels of protection against disease? What is the likelihood that a person will be re-infected?
Many of these questions are still being addressed by health experts, but offer insight into what they have learned.
“Reinfection is relatively rare in people who have recovered from COVID-19, but it can happen. I suspect that people are protected from serious illness for about a year after natural infection, although they can get mild or asymptomatic infections, ”said Dr. Amesh Adalja, principal investigator at Johns Hopkins Center for Health Security. .
Protection after natural infection appears to last for at least six to eight months, although it probably lasts even longer, said Dr William Schaffner, professor of infectious diseases at Vanderbilt University.
He added that researchers are still studying the duration of immunity to infection and are not as confident about the one-year protection period offered as with the shorter periods.
Another uncertainty concerns the impact of variants of the coronavirus on a person’s immunity against a previous infection.
As the coronavirus mutates and more variants emerge, there is evidence that some variants, particularly the beta variant from South Africa, may be able to “overcome natural immunity,” said Dr Adalja, noting that vaccination is necessary to “increase immunity”.
Growing evidence also suggests that those who have been naturally infected with the coronavirus may only need one dose of the two-dose coronavirus vaccine to develop sufficient immunity.
A recent American Chemical Society study found that in participants who contracted COVID-19 prior to vaccination, the first dose produced a “vigorous antibody response similar to severe natural infection,” but the second dose did not. provided no further increase in antibody levels. .
For participants without a previous infection, one dose of Pfizer-BioNTech or Moderna vaccine elicited antibody responses similar to those seen after mild COVID-19 infections, while two doses elicited antibody levels comparable to those seen in mild COVID-19 infections. serious infections.
The Centers for Disease Control and Prevention is actively discussing whether previously infected people should be partially or fully vaccinated, and no official recommendation has yet been made, according to Dr. Schaffner.
Antibody levels after vaccines are higher than after natural infection, which means injections could offer increasingly greater protection against emerging viral variants, the infectious disease specialist noted.
“If we reason analogously to what we know from other vaccines, higher levels of antibodies are generally associated with a longer duration of protection,” said Dr Schaffner.
Investigators at the lab also said that higher levels of antibodies appeared to offer safer and greater protection against the variants.
“This leads to the recommendation that people recovering from Covid should nonetheless be vaccinated,” said Dr Schaffner.
What remains unclear is whether a severe COVID-19 infection offers more protection than a mild infection.
“It appears that people with a more severe infection have, on average, higher levels of antibodies that neutralize the virus and are thought to be able to be protected for longer. But I don’t know if we know for sure, ”said Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine.
“What we do know is that if you’ve been infected and protected and you get a vaccine that appears to give you very high levels of protection,” he said, citing a Rockefeller University study. .
Going forward, Dr Schaffner said more research is needed to find out how long protection against COVID-19 lasts, whether it is from a natural infection or from vaccines, and how long this is. protection is broad.