COVID-19 is caused by infection from SARS-CoV-2, a type of coronavirus. Following SARS-CoV-2 infection, the immune system produces antibodies specific for the SARS-CoV-2 spike protein that prevent reinfection. However, research from early in the COVID-19 pandemic reported a rapid loss of these antibodies a few months after infection. Findings of more recent research suggest SARS-CoV-2 immunity may last longer than previously thought.
B cells are white blood cells that originate in the bone marrow. During an infection, mature B cells enter the bloodstream as plasma cells, where they are activated to produce antibodies specific for the active pathogen. When the infection has resolved, B cells called long-lived bone marrow plasma cells return to the bone marrow where they lie dormant until exposure to the same pathogen reoccurs, providing long-lasting immunity.
The researchers collected blood from 77 patients who had recovered from mild SARS-CoV-2 infection approximately one month following the onset of symptoms and then every three months. They also collected bone marrow samples from 18 participants seven to eight months after infection and from 11 healthy volunteers with no history of SARS-CoV-2 infection or vaccination. Finally, they collected a second bone marrow sample from six participants 11 months after infection.
In the first four months following infection, the concentration of plasma spike antibodies decreased by almost 10 percent; however, this rate slowed over time so that only seven percent of antibodies were lost between four and 11 months. At seven months post-infection, bone marrow samples from most recovered patients contained bone marrow plasma cells specific for SARS-CoV-2, and the concentration of these cells remained stable at 11 months post-infection. Participants had no spike antigen-producing cells in their blood at the time of bone marrow sampling, meaning all antibody-producing cells were located in bone marrow only at 7 and 11 months post-infection.
These findings demonstrate that infection with the SARS-CoV-2 virus results in long-term immunity from long-lived bone marrow plasma cells, even though concentrations of antigen in the bloodstream decrease over time.
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