4.7 Article

Effectiveness of Inactivated COVID-19 Vaccines Against Illness Caused by the B.1.617.2 (Delta) Variant During an Outbreak in Guangdong, China A Cohort Study

Journal

ANNALS OF INTERNAL MEDICINE
Volume 175, Issue 4, Pages 533-+

Publisher

AMER COLL PHYSICIANS
DOI: 10.7326/M21-3509

Keywords

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Funding

  1. National Natural Science Foundation of China [82041030]
  2. Key-Area Research and Development Programof Guangdong Province [2019B111103001]

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Retrospective cohort study suggests that full vaccination with inactivated vaccines is effective against the B.1.617.2 variant, providing protection against infections, symptomatic infections, pneumonia, and severe or critical illness. Partial vaccination shows limited effectiveness.
Background: Real-world evidence on inactivated COVID-19 vaccines against the highly transmissible B.1.617.2 (Delta) variant of SARS-CoV-2 is limited, leaving an important gap in the evidence base about inactivated COVID-19 vaccines for use by immunization programs. Objective: To estimate inactivated vaccine effectiveness (VE) against the B.1.617.2 variant. Design: Retrospective cohort study. Setting: The study was based on the first outbreak of the B.1.617.2 variant in mainland China that was discovered and traced in Guangdong in May and June 2021. Participants: 10 805 adult case patients with laboratory-confirmed infection and close contacts. Measurements: Participants were categorized as unvaccinated, partially vaccinated (1 dose), and fully vaccinated (2 doses). We estimated VE against the primary outcome of pneumonia and the secondary outcomes of infections, symptomatic infections, and severe or critical illness associated with the B.1.617.2 variant. Results: Results are reported in the order of outcome severity. Of 10 805 participants, 1.3% contracted infections, 1.2% developed symptomatic infections, 1.1% had pneumonia, and 0.2% had severe or critical illness. The adjusted VEs of full vaccination were 51.8% (95% CI, 20.3% to 83.2%) against infection, 60.4% (CI, 31.8% to 88.9%) against symptomatic infection, and 78.4% (CI, 56.9% to 99.9%) against pneumonia. Also, full vaccination was 100% (CI, 98.4% to 100.0%) effective against severe or critical illness. By contrast, the adjusted VEs of partial vaccination against infection, symptomatic infection, and pneumonia were 10.7% (CI, -41.2% to 62.6%), 6.8% (CI, -47.4% to 61.0%), and 11.6% (CI, -42.6% to 65.8%), respectively. Limitation: Observational study with possible unmeasured confounders; insufficient data to do reliable subgroup analyses by age and vaccine brand. Conclusion: Full vaccination with inactivated vaccines is effective against the B.1.617.2 variant. Effort should be made to ensure full vaccination of target populations.

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