Clinical and serological predictors of Post COVID-19 Condition: Findings from a Canadian prospective cohort study

Pillar 9
Knowledge, Implementation and Training Team (KITT)

This study found positive associations between Post COVID-19 Condition (PCC), also known as Long COVID, and anti-spike (S), and anti-receptor binding domain (RBD) IgG concentrations, which were not statistically significant, and no association with anti-nucleocapsid (N) IgG concentrations. However, individuals with PCC had significantly higher neutralization efficiency, especially those that reported a deterioration in quality of life.

Key findings:

• Similar proportions of individuals with PCC (66.7%) and infected controls (71.3%) tested positive for infection-acquired antibodies (anti-N). More individuals with PCC tested positive for anti-S (94.1%) and anti-RBD (95.1%) IgG, compared with controls (anti-S: 89.3%; anti-RBD: 84.4%). We observed similar differences among the non-vaccinated subgroup.
• More individuals with PCC were efficient SARS-CoV-2 neutralizers (showing neutralization of ≥85% of SARS-CoV-2 spike protein) than infected controls. In both unvaccinated and vaccinated subgroups, median neutralization efficiency was somewhat higher among individuals with PCC than controls.
• Individuals with PCC who reported deterioration in quality of life due to persistent symptoms had higher IgG titres and median neutralization efficiency. They also had a higher proportion of efficient neutralizers than those with PCC who did not report poorer quality of life.
• Those with PCC were more likely to have allergies and to have sought medical help for their COVID-19 symptoms, as compared to individuals with past COVID-19 infection and no persistent symptoms ≥12 weeks post-infection.
• Individuals with PCC, especially those who reported deterioration in quality of life, were more likely than infected-controls to seek medical help for COVID-19 symptoms and describe complex and enduring health needs long after initial infection.

The study, nested in a prospective study of over 1000 people followed-up at multiple time points for more than two years (Stope the Spread Ottawa / SSO), compared clinical and serological predictors among COVID-19 survivors with (n=102 cases) and without (n=122 controls) persistent symptoms ≥12 weeks post-infection. Participants ranged in age from 21-75 years old. Four primary serological predictors –- anti-N, anti-S, and anti-RBD IgG titres, and neutralization efficiency — were assessed, controlling for pre-determined clinical covariates.

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