Jan. 8, 2021 -- Certain antibodies and memory cells likely last more than eight months after someone has contracted the coronavirus, especially if they have a strong immune response to COVID-19, according to a new study published Wednesday in Science.
Antibodies to the spike protein on the coronavirus were relatively stable after six months, and spike-specific memory B cells were higher at six months than the first month after infection. The number of memory T cells declined in about four to six months, but there were some that lasted.
“That amount of memory would likely prevent the vast majority of people from getting hospitalized disease, severe disease, for many years,” Shane Crotty, the senior author and a virologist at the La Jolla Institute of Immunology, told The New York Times.
The research team analyzed 254 blood samples from 188 COVID-19 patients across the country who had a range of disease, including asymptomatic, mild, moderate, and severe cases. Most had a mild case of COVID-19, and 93% were never hospitalized. Researchers also looked at 43 samples taken more than six months after symptoms started, up to eight months post-infection.
They found that neutralizing antibodies were stable between one to eight months after infection and that these antibodies gradually declined over time but seemed to last.
Memory B cells, which remember a virus to make antibodies, increased during the first four months after infection and then plateaued but lasted in nearly all of the cases after eight months.
Memory T cells, which recognize antigens on a virus and trigger an immune response, appeared within a month of infection and began a slow decline about four to six months after infection but also lasted. This is similar for other viruses that cause the flu and yellow fever.
Specific “helper” T cells necessary for creating neutralizing antibodies and long-lasting immunity were present in nearly all of the samples analyzed and lasted for more than six months.
Antibodies and memory B cells were higher in the patients who were hospitalized, which could mean that those with more severe COVID-19 may build up greater long-term immunity.
Overall, 64% of the cases had all five of the immune memory responses that were studied, appearing in the first or second month after infection. After five to eight months, that dropped to 43%. However, 95% of the patients still had at least three of the five immunity categories after five months.
Although researchers can’t make direct conclusions about COVID-19 immunity based on the levels of antibodies or memory cells in the samples, the findings seem promising. This might mean that an immune response could reduce reinfections, viral load, and disease severity in patients in the future. A few COVID-19 reinfections have been reported, but they tend to be asymptomatic or less severe, the authors wrote.
“Durable immunity against secondary COVID-19 disease is a possibility in most individuals,” they wrote.