Protective Immunity Against COVID-19 Could Last Months

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

Science published this study’s findings on January 6, 2021, 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 severe disease from the SARS-CoV-2 virus for months, perhaps years after infection, reported Madeline McCurry-Schmidt, a reporter with La Jolla Institute for Immunology (LJI).

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 wouldn’t be equipped to defend itself against reinfection.

The researchers found that virus-specific antibodies do persist in the bloodstream months after infection. Importantly the body also has immune cells called memory B cells at the ready. If a person reencounters SARS-CoV-2, these memory B cells could reactivate and produce SARS-CoV-2 antibodies to fight re-infection.

“We measured antibodies, memory B cells, helper T cells and killer T cells all at the same time,” added 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.”

LJI Professor Alessandro Sette explained ‘that a decline in antibodies is very normal. “Of course, the immune response decreases over time to a certain extent, but that’s normal. 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 SARS-CoV-2 virus uses its “spike” protein to initiate human cells’ infection, so the researchers looked for memory B cells specific for the SARS-CoV-2 spike. They found that spike-specific memory B cells 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, prepared 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 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.

“This implies that there’s a good chance people would have protective immunity, at least against serious disease, for that time, and probably well beyond that,” says Crotty.

The team cautions that protective immunity does vary dramatically from person to person.

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.

“There are some people that are way down at the bottom of how much immune memory they have, and maybe those people are a lot more susceptible to reinfection,” Crotty stated.

The fact that immune memory against SARS-CoV-2 is possible is also a good sign for vaccine developers.

The researchers stated they would 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 research team is also working to understand how immune memory differs across people of different ages and how that may influence COVID-19 case severity.

This research was supported by the National Institutes of Health’s National Institute for Allergy and Infectious Disease. The research team disclosed no industry conflicts of interest.

The La Jolla Institute for Immunology is dedicated to understanding the intricacies and power of the immune system so that we may apply that knowledge to promote human health and prevent a wide range of diseases.

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