Elevated antibodies and immune cells associated with prior infection level out within six months of vaccination and need to be replenished with regular booster shots.
Researchers have concluded after a three-year study that prior infection by the virus that causes COVID-19 does not provide long-lasting immunity against reinfection. The data comes from one of the most long-term and rigorous COVID studies to date and reinforces the fact that immunity must be maintained by regular booster shots to protect against reinfection, regardless of an individual's previous infection status.
"I think most of us know someone who has gotten a case of COVID-19 and assumed it "primed" them to improve their response to the vaccine or to protect them from getting severe cases in the future," says Vanessa Silva-Moraes, PhD, a Cleveland Clinic research associate and first author of the study published in Immunohorizons. "If you look at antigen levels a month after infection, it might seem true, but we found that if you look at the levels of people 90 or 180 days later, the elevated response goes down. In the long term, these individuals have the same risk of getting an infection as someone who was not infected at all."
Dr. Silva-Moraes began the study in October 2020 as a postdoctoral researcher in the laboratory of Ted Ross, PhD. At the time, many people still had not been infected by the virus. The vaccine had not been released yet either.
"These conditions provided us the unique opportunity to see how getting the virus influenced the way people responded to vaccines and future infections," she says.
Over the next three years, Dr. Silva-Moraes led a team in analyzing immune levels in blood samples of 40 study participants, half of whom ended up contracting an infection and half of whom did not. Researchers were looking to see whether a previous COVID-19 infection influenced how patients responded to being vaccinated.
Participants were tested monthly until the mRNA vaccine was released in 2021 and three times after each of their first three shots: 30, 90, and 180 days. Dr. Silva-Moraes' team then analyzed the participants' antibodies levels against SARS-CoV-2, as well as their cellular immunity. Significantly elevated levels of either immune marker mean the individual was likely protected against the virus.
Drs. Ross and Silva-Moraes were not surprised to see that individuals who had previously been infected responded better to vaccination in the short term. One month after receiving their shots, antibodies and immune cell levels were significantly higher in these individuals' bloodstreams. What did surprise them was what happened in the following months: by 3 months after their shots, there was no difference in immune levels between the two groups. This was especially true after the second and third boosters.
Dr. Ross, Global Director of Vaccine Development at Cleveland Clinic, says that these long-term studies are important to evaluate the safety and effectiveness of new vaccines, so healthcare providers and drug designers can quickly make changes and improvements as necessary.
"Vaccines need to provide long-lasting protection against everyone, regardless of their demographics or health status," he says. "This includes factors like preimmunity to the virus. In the case of COVID-19, our results highlighted the importance of receiving regular boosters even after catching the virus."
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