Both cellular and humoral immunity are important in the defense against viral infections, and a study by Breton and colleagues[ evaluated the cellular immune response to SARS-CoV-2 among 41 adult patients with a previous positive reverse-transcriptase polymerase chain reaction test for the virus. The sample was 63.4% male and represented a wide range of ages. Most participants had mild COVID-19. Participants were followed for 6 months to assess the durability of the cellular immune response to SARS-CoV-2.
The proportion of cluster of differentiation (CD)4+ T cells decreased at 1.3 months after infection whereas the concentration of CD8+ T cells increased at this time. By 6.1 months after infection, levels of both CD4+ and CD8+ T cells had returned to physiologic levels. Central memory CD4+ and CD8+ T cells also decreased by month 6.
On in vitro testing with SARS-CoV-2 peptides, convalescent plasma from participants demonstrated a robust response of memory markers and inflammatory molecules. This response declined by only 22% to 32% by month 6.1 after infection. As a comparison, the inflammatory responses to cytomegalovirus peptides remained unchanged over the 6-month study period.
The authors concluded that a robust cellular immune response is likely for at least 6 months after infection with SARS-CoV-2, but what about the humoral response? Another study by Turner and colleagues examines this issue and is summarized under “Study Highlights.”
Study Synopsis and Perspective
Immunity to the novel coronavirus could last for a year — and possibly longer — particularly after COVID-19 vaccination.
Two recent studies indicate that most people who contracted COVID-19 recovered and then got vaccinated later may not need a booster shot, according to The New York Times. Those individuals who were never infected and then got vaccinated may need a booster shot later.
Both studies looked at people who were exposed to COVID-19 about a year ago. Scientists found that certain immune cells may survive in the bone marrow of people who were infected and later vaccinated. Those immune cells may create antibodies whenever needed.
In another study published on the bioRxiv preprint server, researchers found that these memory B cells can grow and strengthen for at least 12 months after an initial infection. This study has not yet been peer-reviewed.
“The papers are consistent with the growing body of literature that suggests that immunity elicited by infection and vaccination for SARS-CoV-2 appears to be long-lived,” .
“The reason we get infected with common coronaviruses repetitively throughout life might have much more to do with variation of these viruses rather than immunity,”.
In the Nature study, researchers analyzed blood samples from 77 people at 3-month intervals, starting about a month after their infection. Of those individuals, 6 were hospitalized for COVID-19, and the rest had mild symptoms. The blood levels of antibodies fell sharply after infection, but the memory B cells remained in the bone marrow.
Among 19 bone marrow samples, 15 had detectable memory B cells about 7 months after infection. The other 4 did not, which could mean that some people who contract the virus do not generate a long-lasting response. The finding backs up the idea that people who have recovered from COVID-19 should be vaccinated.
“It means that even if you got infected, it doesn’t mean that you have a super immune response,”.
In the bioRxiv study, researchers analyzed blood samples from 63 people who recovered from COVID-19 about a year before. Most had mild symptoms, and 26 had received at least one dose of the Pfizer or Moderna vaccine. The neutralizing antibodies, which prevent reinfection, were unchanged between about 6 to 12 months in those individuals who had been vaccinated.
As the memory B cells matured and evolved, they were also able to neutralize some variants, the researchers found. Those persons who had not been vaccinated had lower neutralizing activity against all forms of the virus, particularly against the B.1.351 variant first identified in South Africa. That means people who have had COVID-19 and a vaccine may not need a booster, but those persons who have only contracted the virus or only been inoculated may eventually need one.
“People who were infected and get vaccinated really have a terrific response, a terrific set of antibodies, because they continue to evolve their antibodies,” . “I expect that they will last for a long time.”