In a new study, researchers found that nearly all COVID-19 survivors have the immune cells necessary to fight re-infection.
They suggest that the immunity can last for at least eight months after the onset of symptoms from the initial infection.
The findings are based on analyses of blood samples from 188 COVID-19 patients.
They 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 research was conducted by a team at La Jolla Institute for Immunology.
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.
In the study, the team 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 encounters SARS-CoV-2 again, these memory B cells could reactivate and produce SARS-CoV-2 antibodies to fight re-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 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 team says 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.
They caution that protective immunity does vary dramatically from person to person.
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.
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.
One author of the study is LJI Professor Alessandro Sette, Dr. Biol. Sci.
The study is published in Science.
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