Effects of antiviral treatment and recent vaccination on limiting probable transmission of COVID-19 in household

Introduction

Antiviral treatment and prior vaccination reduce the progression to severe COVID-19. Yet, their effectiveness in preventing onward transmission was understudied. This study evaluates the impact of antiviral treatment and recent vaccination on the risk of probable COVID-19 transmission in households.

Material and Methods

In a population cohort study in Hong Kong, participants were asked to detail any incident SARS-CoV-2 infections through monthly surveys. For episodes reported to have acquired from a non-household source, any presentation of respiratory symptoms among co-living members in the same month was enquired. Presuming a secondary attack, the likelihood of household transmission was assessed in cases with and without receiving antiviral treatment and recent vaccination (within 3 months) using multiple logistic regression, controlling for demographics and household size.

Results

Between January 2023 and January 2024, totally 883 non-hospitalised COVID-19 episodes were reported by 866 participants with 40% male and a median age of 48 years (IQR 36-58). Among 773 episodes (89%) with medical follow-up, 22% were prescribed with either molnupiravir or nirmatrelvir/ritonavir. Among cases with antivirals prescribed, respiratory symptoms emerged in 39% of their co-living members as a sign of household transmission, compared to 49% and 55% among those without antiviral prescription and seeking medical advice, respectively. Likewise, symptom presentation was less commonly reported in co-living members of cases who were recently vaccinated (39% vs 49%). Assuming that those symptoms resulted from secondary attacks, cases treated with antivirals were significantly less likely to generate onward transmission, relative to those without prescription (adjusted odds ratio [aOR] 0.90) and seeking consultation (aOR 0.86). With no similar association identified for recently vaccinated cases, a significantly shorter symptomatic period was however noted (5.45 vs 7.55 days).

Discussion

The use of COVID-19 antivirals could likely mitigate one's infectiousness. Complementary to timely vaccination for abridging symptomatic illness, antiviral treatment should be initiated early to limit onward transmission.