People's immune responses to COVID-19 after inoculation were lower among those who were previously infected with SARS-CoV-2 than those who were not, according to a study the National Institutes of Health published March 20.
The researchers, led by Mark Davis, PhD, the director of Stanford Institute for Immunity, Transplantation and Infection in Palo Alto, Calif., found that vaccination with Pfizer's two-dose series among those who have never had COVID-19 "induced robust CD4+ and CD8+ T-cell responses to the virus' spike protein."
The results are published in Immunity.
Those who had a past COVID-19 infection before being vaccinated with the Pfizer shots "produced spike-specific CD8+ T cells at considerably lower levels — and with less functionality — than people who were never infected. This immunity status "substantially" decreased among a third group of study participants who were never vaccinated.
"This dysfunction persists for a year or more after the active phase of infection, suggesting lasting damage, despite the absence or near absence of the relevant virus," the researchers said in Immunity. "In this context, it may be that these attenuated CD8+ T cell responses contribute to long COVID, perhaps rendering patients unable to respond robustly to subsequent infections by SARS-CoV-2 variants or other pathogens."