AI Article Synopsis

  • Limited real-world evidence exists on the effectiveness of inactivated COVID-19 vaccines against the Delta variant, prompting this study to assess their efficacy.
  • The study analyzed data from 10,805 adults during the first Delta outbreak in China, categorizing participants by their vaccination status (unvaccinated, partially vaccinated, fully vaccinated).
  • Full vaccination showed significant effectiveness against infection, symptomatic cases, and pneumonia, with 100% effectiveness against severe illness, while partial vaccination had much lower effectiveness levels.

Article Abstract

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.

Primary Funding Source: National Natural Science Foundation of China and Key-Area Research and Development Program of Guangdong Province.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8819853PMC
http://dx.doi.org/10.7326/M21-3509DOI Listing

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