New research published in The Lancet Respiratory Medicine has found that seropositive healthy young adults are still at risk of reinfection.

A prospective cohort study was conducted as part of the COVID-19 Health Action Response for Marines study (CHARM) to examine the risk of reinfection in healthy young adults who were seropositive for a previous SARS-CoV-2 infection. The study included male recruits, aged 18–20 years, from the US Marine Corps. They were first put under a two-week unsupervised home quarantine followed by a two-week supervised quarantine when they returned to the marine quarantine facility.

• Seropositive young adults had lower risk of reinfection vis a vis the seronegative individuals. During the 6-week study period, 10% of seropositive participants (19 / 189) had at least one positive PCR test for SARS-CoV-2. On the other hand, 48% of seronegative participants (1079 of 2247) tested positive for the infection.
• Reinfection in seropositive adults was found to be associated with lower spike protein IgG titers vs those who had higher IgG titers (hazard ratio 0·45 [95% CI 0·32–0·65]; p<0·001).
• The infected seropositive subjects had at least 10 times lower viral load than that seen in the infected seronegative participants (ORF1ab gene cycle threshold difference 3·95 [95% CI 1·23–6·67]; p=0·004).
• Baseline neutralizing titers were detected in 83% (45/54) of uninfected seropositive subjects and 32% (6/19) of the infected subjects.

These observations indicate that although antibodies produced as a result of the infection are generally protective, they do no ensure effective immunity against subsequent infection. A risk still exists albeit a small one. In previously infected young adults, vaccination further enhances the natural immune response to prevent reinfection and reduce transmission. Hence, an aggressive vaccination strategy needs to be pursued to slow down the pandemic.

(Source: Lancet Respiratory Medicine, Published April 15, 2021)

Dr KK Aggarwal

President CMAAO, HCFI and Past National President IMA