COVID-19 Survivors Have Immune Cells Necessary to Fight Re-Infection Until Eight Months, Suggests New Data

New data suggest that nearly all COVID-19 survivors have the immune cells necessary to fight re-infection.

The findings by scientists at the La Jolla Institute for Immunology (LJI; La Jolla, CA, USA), based on their analyses of blood samples from 188 COVID-19 patients, suggest that responses to the novel coronavirus, SARS-CoV-2, from all major players in the “adaptive” immune system, which learns to fight specific pathogens, can last for at least eight months after the onset of symptoms from the initial infection. The findings could mean that COVID-19 survivors have protective immunity against serious disease from the SARS-CoV-2 virus for months, perhaps years after infection.

The SARS-CoV-2 virus uses its “spike” protein to initiate infection of human cells, so the researchers looked for memory B cells specific for the SARS-CoV-2 spike. They found that spike-specific memory B cells actually increased in the blood six months after infection. COVID-19 survivors also had an army of T cells ready to fight reinfection. Memory CD4+ “helper” T cells lingered, ready to trigger an immune response if they saw SARS-CoV-2 again. Many memory CB8+ “killer” T cells also remained, ready to destroy infected cells and halt a reinfection. The different parts of the adaptive immune system work together, so seeing COVID-fighting antibodies, memory B cells, memory CD4+ T cells and memory CD8+ T cells in the blood more than eight months following infection is a good sign.

The new study helps clarify some concerning COVID-19 data from other labs, which showed a dramatic drop-off of COVID-fighting antibodies in the months following infection. Some feared that this decline in antibodies meant that the body would not be equipped to defend itself against reinfection. However, the researchers caution that protective immunity does vary dramatically from person to person. In fact, the researchers saw a 100-fold range in the magnitude of immune memory. People with a weak immune memory may be vulnerable to a case of recurrent COVID-19 in the future, or they may be more likely to infect others. Nevertheless, the fact that immune memory against SARS-CoV-2 is possible is also a good sign for vaccine developers. The researchers will continue to analyze samples from COVID-19 patients in the coming months and hope to track their responses 12 to 18 months after the onset of symptoms. The team is also working to understand how immune memory differs across people of different ages and how that may influence COVID-19 case severity.

“Our data suggest that the immune response is there - and it stays,” LJI Professor Alessandro Sette, Dr. Biol. Sci., who co-led the study.

“We measured antibodies, memory B cells, helper T cells and killer T cells all at the same time,” said LJI Professor Shane Crotty, Ph.D. “As far as we know, this is the largest study ever, for any acute infection, that has measured all four of those components of immune memory.”

“It is possible that immune memory will be similarly long lasting similar following vaccination, but we will have to wait until the data come in to be able to tell for sure,” said LJI Research Assistant Professor Daniela Weiskopf, Ph.D. “Several months ago, our studies showed that natural infection induced a strong response, and this study now shows that the responses lasts. The vaccine studies are at the initial stages, and so far have been associated with strong protection. We are hopeful that a similar pattern of responses lasting over time will also emerge for the vaccine-induced responses.”

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La Jolla Institute for Immunology