Effectiveness of Vaccines and Antiviral Drugs in Preventing Severe and Fatal COVID-19, Hong Kong

Emerg Infect Dis. 2024 Jan;30(1):70-78. doi: 10.3201/eid3001.230414. Epub 2023 Dec 1.


We compared the effectiveness and interactions of molnupiravir and nirmatrelvir/ritonavir and 2 vaccines, CoronaVac and Comirnaty, in a large population of inpatients with COVID-19 in Hong Kong. Both the oral antiviral drugs and vaccines were associated with lower risks for all-cause mortality and progression to serious/critical/fatal conditions (study outcomes). No significant interaction effects were observed between the antiviral drugs and vaccinations; their joint effects were additive. If antiviral drugs were prescribed within 5 days of confirmed COVID-19 diagnosis, usage was associated with lower risks for the target outcomes for patients >60, but not <60, years of age; no significant clinical benefit was found if prescribed beyond 5 days. Among patients >80 years of age, 3-4 doses of Comirnaty vaccine were associated with significantly lower risks for target outcomes. Policies should encourage COVID-19 vaccination, and oral antivirals should be made accessible to infected persons within 5 days of confirmed diagnosis.

Keywords: COVID-19; Comirnaty; CoronaVac; Hong Kong; SARS; SARS-CoV-2; coronavirus; coronavirus disease; molnupiravir; nirmatrelvir; respiratory infections; ritonavir; severe acute respiratory syndrome coronavirus 2; viruses; zoonoses.

MeSH terms

  • Antiviral Agents / therapeutic use
  • BNT162 Vaccine
  • COVID-19 Testing
  • COVID-19 Vaccines
  • COVID-19* / prevention & control
  • Child, Preschool
  • Hong Kong / epidemiology
  • Humans
  • Vaccines*


  • COVID-19 Vaccines
  • BNT162 Vaccine
  • Vaccines
  • Antiviral Agents