The new data suggests that almost all COVID-19 survivors have the immune cells necessary to fight reinfection.
Findings from scientists at the La Jolla Institute of Immunology (LJI; La Jolla, CA, USA), based on their analysis of blood samples from 188 COVID-19 patients, suggest that responses to the novel coronavirus, SARS-CoV -2, of all the 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 of the initial infection. The findings could mean that COVID-19 survivors have protective immunity against the severe SARS-CoV-2 virus disease for months, perhaps years after infection.
The SARS-CoV-2 virus uses its Spike protein to initiate infection in human cells, so the researchers looked for memory B cells specific for this SARS-CoV-2 protein. They found that memory B cells specific for the Spike protein actually increased in the blood six months after infection. The COVID-19 survivors also had an army of T cells ready to fight reinfection. The memory CD4 + “helper” T cells remained, ready to trigger an immune response if they saw SARS-CoV-2 again. There were also plenty of memory CB8 + “killer” T cells left, ready to destroy infected cells and stop 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 after infection, is a good sign.
The new study helps clarify some data on COVID-19 from other labs, which showed a dramatic drop in COVID-fighting antibodies in the months after infection. Some feared that this decrease in antibodies meant that the body would not be equipped to defend itself against reinfection. However, the researchers caution that protective immunity varies dramatically from person to person. In fact, the researchers saw a 100-fold range in the magnitude of immune memory. People with weak immune memory may be vulnerable to a recurrence of COVID-19 in the future, or they may be more likely to infect other people. However, the fact that immune memory against SARS-CoV-2 is possible is also a good sign for vaccine developers. Researchers will continue to test samples from COVID-19 patients in the coming months and hope to track their responses 12 to 18 months after symptoms appear. The team has also worked to understand how immune memory differs between people of different ages and how that can influence the severity of the COVID-19 case.
“Our data suggest that the immune response is there, and it remains,” said LJI professor Alessandro Sette, Ph.D. in Biological Sciences, who co-led the study.
“We measure antibodies, memory B cells, helper T cells, and killer T cells all at the same time,” said Professor Shane Crotty, Ph.D. of the LJI. “To our knowledge, this is the largest study ever conducted, for any acute infection, that has measured all four components of immune memory.”
“Immune memory may be just as durable after vaccination, but we will have to wait until the data comes in before we can be 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 responses last. Vaccine studies are in the early stages and have so far been associated with strong protection. We are hopeful that a similar pattern of long-lasting responses will emerge for vaccine-induced responses as well. “
La Jolla Institute of Immunology