Body’s immunity against coronavirus could last 8 months or more, La Jolla researchers say
New data suggest that nearly all COVID-19 survivors have the immune cells necessary to fight reinfection for months if not years, according to researchers at the La Jolla Institute for Immunology.
The findings, based on analyses of blood samples from 188 COVID-19 patients, suggest that responses to the coronavirus SARS-CoV-2 — which causes the disease — from all major players in the “adaptive” immune system can last for at least eight months after the onset of symptoms from the initial infection. The adaptive immune system learns to fight specific pathogens.
“Our data suggest that the immune response is there and it stays,” said LJI professor Alessandro Sette, who co-led the study with professor Shane Crotty and research assistant professor Daniela Weiskopf.
“We measured antibodies, memory B cells, helper T cells and killer T cells all at the same time,” Crotty said. “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.”
The findings, published in the Jan. 6 online edition of the journal Science, could mean that COVID-19 survivors have protective immunity against serious disease from the coronavirus for months, perhaps years after infection.
The new study helps clarify some concerning COVID-19 data from other labs that showed a dramatic drop-off of COVID-fighting antibodies in the months following infection. Some feared that meant the body wouldn’t be equipped to defend itself against reinfection.
“Of course, the immune response decreases over time to a certain extent, but that’s normal,” Sette said. “That’s what immune responses do. They have a first phase of ramping up, and after that fantastic expansion, eventually the immune response contracts somewhat and gets to a steady state.”
The researchers found that virus-specific antibodies persist in the bloodstream months after infection. The body also has immune cells called memory B cells at the ready. If a person encounters SARS-CoV-2 again, the memory B cells could reactivate and produce antibodies to fight reinfection.
SARS-CoV-2 uses its “spike” protein to initiate infection of human cells, so the researchers looked for memory B cells specific for that 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, Crotty said.
“This implies that there’s a good chance people would have protective immunity, at least against serious disease, for that period of time and probably well beyond that,” he said.
The team cautioned that protective immunity varies dramatically from person to person. In fact, the researchers saw a hundredfold range in the magnitude of immune memory. People who are “way down at the bottom of how much immune memory they have” may be vulnerable to recurrent COVID-19, Crotty said.
The fact that immune memory against SARS-CoV-2 is possible is also a good sign for vaccine developers, said Weiskopf, who emphasized that the study tracked responses to natural SARS-CoV-2 infection, not immune memory after vaccination.
“It is possible that immune memory will be similarly long-lasting following vaccination, but we will have to wait until the data come in to be able to tell for sure,” Weiskopf said. “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.”
The researchers will continue to analyze samples from COVID-19 patients in coming months and hope to track their responses 12 to 18 months after the onset of symptoms.
“We are also doing very detailed analyses at a much, much higher granularity on what pieces of the virus are recognized,” Sette said.
In addition, the team is working to understand how immune memory differs across people of different ages and how that may influence the severity of COVID-19 cases. ◆
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