Do your patients think that getting COVID-19 is fully protective against subsequent reinfection? Tell it to the Marines.
A study of U.S. Marine recruits on their way to boot camp at Parris Island, S.C., showed that those who were seropositive at baseline, indicating prior exposure to SARS-CoV-2, remained at some risk for reinfection. They had about one-fifth the risk of subsequent infection, compared with seronegative recruits during basic training, but reinfections did occur.
The study, by Stuart C. Sealfon, MD, of Icahn School of Medicine at Mount Sinai in New York, and colleagues, was published in The Lancet Respiratory Medicine.
“Although antibodies induced by initial infection are largely protective, they do not guarantee effective SARS-CoV-2 neutralization activity or immunity against subsequent infection,” they wrote.
An infectious disease specialist who was not involved in the study said that the findings provide further evidence about the level of immunity acquired after an infection.
“It’s quite clear that reinfections do occur, they are of public health importance, and they’re something we need to be mindful of in terms of advising patients about whether a prior infection protects them from reinfection,” Mark Siedner, MD, MPH, a clinician and researcher in the division of infectious diseases at Massachusetts General Hospital, Boston, said in an interview.
The study results reinforce that “not all antibodies are the same,” said Sachin Gupta, MD, an attending physician in pulmonary and critical care medicine at Alameda Health System in Oakland, Calif. “We’re seeing still that 10% of folks who have antibodies can get infected again,” he said in an interview.
Dr. Sachin Gupta
CHARM initiative
Dr. Sealfon and colleagues presented an analysis of data from the ironically named CHARM (COVID-19 Health Action Response for Marines) prospective study.
CHARM included U.S. Marine recruits, most of them male, aged 18-20 years, who were instructed to follow a 2-week unsupervised quarantine at home, after which they reported to a Marine-supervised facility for an additional 2-week quarantine.
At baseline, participants were tested for SARS-CoV-2 immunoglobulin G (IgG) seropositivity, defined as a dilution of 1:150 or more on receptor-binding domain and full-length spike protein enzyme-linked immunosorbent assay (ELISA).
The recruits filled out questionnaires asking them to report any of 14 specific COVID-19–related symptoms or any other unspecified symptom, as well as demographic information, risk factors, and a brief medical history.
Investigators tested recruits for SARS-CoV-2 infection by polymerase chain reaction (PCR) assay at weeks 0, 1, and 2 of quarantine, and any who had positive PCR results during quarantine were excluded.
Participants who had three negative swab PCR results during quarantine and a baseline serology test at the beginning of the supervised quarantine period – either seronegative or seropositive – then went on to enjoy their basic training at the Marine Corps Recruit Depot, Parris Island, S.C.
The participants were followed prospectively with PCR tests at weeks 2, 4, and 6 in both the seropositive and seronegative groups, and sera were obtained at the same time.