(356) The Persistence in Risk and Effect Of COVID-19 Vaccination on Long-Term Health Consequences One Year After SARS-Cov-2 Infection: A Territory-Wide Cohort Study in Hong Kong

Background: The persisting risk of long-term health consequences of COVID-19 infection and the protection against such risk conferred by COVID-19 vaccination on the risk of remains largely unknown.

Objectives: This study evaluated the progressive risk of clinical sequelae and compared the risk between patients of different COVID-19 vaccination status over one year following COVID-19 infection.

Methods: A retrospective territory-wide cohort study was conducted using electronic medical record from the Hong Kong Hospital Authority (HKHA) database. 1,175,277 patients with COVID-19 infection between April 1st and 2020 and October 31st, 2022 aged 18 or above, stratified into unvaccinated (received 0 dose), incompletely vaccinated (1 dose), fully vaccinated (2 doses) and received booster (≥3 doses) of BioNtech or CoronaVac COVID-19 vaccines and non-COVID-19 controls matched by the exact birth-year and sex. Covariates between patients with COVID-19 infection and non-COVID-19 controls were adjusted using propensity score-based inverse probability treatment weighting. The hazard ratio of evidence-based list of reported clinical sequelae, cardiovascular and all-cause mortality between participants with a confirmed COVID-19 infection and their matched controls at three-monthly interval up to one year of COVID-19 infection were estimated using Cox proportional regression model.

Results: A progressive reduction in risk of all-cause mortality was observed over one year between patients with COVID-19 infection and non-COVID-19 controls [dose=0, 0-30d: 18.89 (18.07,19.74); 31-90d: 3.79 (3.56,4.03); 91-180d: 2.11 (1.97,2.26); 181-270d: 1.97 (1.83,2.13); 271-365d: 2.12 (1.92,2.33)]. Patients with complete vaccination or have received booster dose incurred a lower risk of health consequences including major cardiovascular diseases [dose=0: 1.93 (1.67,2.22); dose=2: 1.06 (0.94,1.20); dose≥3: 1.11 (0.98,1.25)], and all-cause mortality [dose=0: 3.79 (3.56,4.03); dose=2: 1.11 (1.02,1.21); dose≥3: 0.87 (0.76,0.99)] than unvaccinated or patients with incomplete vaccination 30-90 days after infection. Completely vaccinated and patients with booster dose of vaccines did not incur significant higher risk of health consequences from 271 and 91 days of infection onwards, respectively, whilst unvaccinated and incompletely vaccinated patients continued to incur a greater risk of clinical sequelae for up to a year following COVID-19 infection.

Conclusions: The study findings reported a progressive reduction in risk of health consequences following COVID-19 infection over a year and provided real-world evidence supporting the effectiveness of COVID-19 vaccines in reducing the risk of long-term health consequences of COVID-19 infection and its persistence.