Analysis of COVID-19 immune response post-infection points to protective immunity

Researchers who studied antibody and immune cell responses in more than 180 men and women who had recovered from the novel coronavirus (COVID-19) reported that these patients' immune memory to the virus, across all immune cell types studied, was measurable for up to eight months after symptoms appeared, according to new research published in the journal Science.

The results indicate "that durable immunity against secondary COVID-19 disease is a possibility in most individuals," the authors said.

As the number of daily COVID-19 cases worldwide continues to mount, whether an initial infection with SARS-CoV-2 leads to long-lasting protective immunity against COVID-19 remains a question. Studying the nature of the humoral response to the virus, which includes an antibody response, and of the cellular immune response, which includes B cells and T cells, over periods of six months after symptoms start could help inform protective immunity's duration.

To do this, the researchers recruited more than 180 men and women from the United States who had recovered from the disease. The majority had had mild symptoms that did not require hospitalization, though 7 percent were hospitalized.

Most subjects provided a blood sample at a single time point, between six days and eight months after symptoms took hold, though 43 samples were provided at six months or more following symptom onset, according to the study.

In 254 total samples from 188 COVID-19 cases, the researchers tracked antibodies, B cells, which produce more antibodies, and two types of T cells, which kill cells that are infected. Antibodies, including to viral spike protein components, only exhibited modest declines at six to eight months after symptom onset. T cells, meanwhile, showed only a slight decay in the body, while B cells that recognized features of the SARS-CoV-2 virus grew in number in some cases, the study said.  

While the authors caution that "direct conclusions about protective immunity cannot be made on the basis of [their findings] because mechanisms of protective immunity against SARS-CoV-2 or COVID-19 are not defined in humans," they also said that several "reasonable interpretations" can be made from their study. These include support for resting immune memory compartments potentially contributing "in meaningful ways to protective immunity against pneumonia or severe secondary COVID-19," the authors said.

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