Association of COVID-19 Vaccination and Clinical Severity of Patients Infected with Delta or Omicron Variants — China, May 21, 2021–February 28, 2022

WHAT IS ALREADY KNOWN ABOUT THIS TOPIC? Compared with the international mRNA and adenovirus-vectored coronavirus disease 2019 (COVID-19) vaccines, there is less real-world research data about breakthrough cases in people vaccinated with China-made COVID-19 vaccines. Analyses of clinical outcomes of breakthrough cases will be an important supplement to the clinical trial efficacy and observational effectiveness data of China-made COVID-19 vaccines. WHAT IS ADDED BY THIS REPORT? COVID-19 vaccine age-eligible individuals (≥3 years old) who received full primary series and a booster dose of China-made COVID-19 vaccines had good protection from pneumonia caused by Delta variant infection. There was only one serious Delta case in children (unvaccinated), but among adults 18 years and older, there was good protection from serious illness with primary vaccination and booster vaccination. Among people ≥60 years, full vaccination and booster vaccination were associated with protection from pneumonia and risk of serious COVID-19 caused by Omicron variant infection. There were few serious Omicron cases. WHAT ARE THE IMPLICATIONS FOR PUBLIC HEALTH PRACTICE? Everyone 3 years and older without contraindications should be fully vaccinated against COVID-19; schedule-eligible adults should receive booster doses. The pace of booster dose administration, especially among the elderly, should be accelerated.