https://www.sciencedaily.com/releases/2021/11/211111130417.htm

"Most individuals with a previous SARS-CoV-2 infection seem to be protected from the virus for many months or even longer, yet some individuals can become infected again with the virus only a few months later," said Manish Sagar, MD, an infectious diseases physician at Boston Medical Center. "We conducted this study to understand whether cases of re-infection with SARS-CoV-2 are associated with any demographic characteristics or if reinfection is due to a deficiency in the patient's immune response."

Using electronic medical record data from Boston Medical Center patients, individuals who tested positive for SARS-CoV-2 who tested positive again for SARS-CoV-2 after at least 90 days after initial infection were included in the study cohort (n=75). All individuals that tested negative at least 90 days after an initial SARS-CoV-2 infection were included and classified as the convalescent group (n=1,594). The researchers compared many clinical and demographical characteristics, such as age, sex, and comorbidities, between the reinfection and convalescent group. Next, plasma from a smaller subset of patients in each of the two groups was tested for the presence of antibodies that recognize SARS-CoV-2. To confirm re-infection, the researchers sequenced the virus from a few patients after their first infection and compared it to a virus from the same patient after their second infection. No individuals in this study received a COVID-19 vaccine given that the data were collected prior to the public availability of these vaccines.