Study: Previous COVID-19 Infection Doesn’t Fully Protect Against Reinfection in Young People

Antibodies introduced by SARS-CoV-2, while largely protective, do not completely protect against reinfection in young people, according to a longitudinal, prospective study of more than 3000 young, healthy members of the US Marines Corps, which was published in The Lancet.

Conducted between May 2020 and November 2020, the study found that more than 10% of participants who were previously infected with SARS-CoV-2 (seropositive) became reinfected, compared with new infections in 50% of participants who had not been previously infected (seronegative). The population consisted of 3249 predominantly male Marine recruits between 18 and 20 years of age.

Participants were assessed for seropositivity upon arrival at a Marine-supervised 2-week quarantine and tested for SARS-CoV-2 at initiation, middle, and end of quarantine via polymerase chain reaction (PCR). The study team then performed 3 bi-weekly PCR tests in both seronegative and seropositive groups once the recruits left quarantine and entered basic training.

Recruits who tested positive for a new second COVID-19 infection during the study were isolated and received additional testing. Levels of neutralizing antibodies were also taken from subsequently infected seropositive and selected seropositive participants who were not reinfected during the study period.

The researchers studied the reinfected and not infected participants' antibody responses in order to understand why the reinfections occurred. According to the study, within the seropositive group, participants who became reinfected had lower antibody levels against the SARS-CoV-2 virus than those who did not become reinfected.

Additionally, neutralizing antibodies were less common in those who became reinfected. A majority of the new COVID-19 cases in the study were asymptomatic or had mild symptoms, and none were hospitalized.

Viral load among reinfected seropositive recruits was 10 times lower than in infected seronegative participants. This finding is significant enough to mean that some reinfected individuals could still have a capacity to transmit infection, according to the study authors, who noted that this requires further investigation to confirm.

REFERENCE

Study shows past COVID-19 infection doesn't fully protect young people against reinfection [news release]. EurekAlert; April 16, 2021. Accessed April 20, 2021. https://www.eurekalert.org/pub_releases/2021-04/tmsh-ssp041621.php