Comparative Effectiveness of Coronavirus Disease 2019 (COVID-19) Vaccines Against the Delta Variant

Malcolm Risk, Chen Shen, Salim S. Hayek, Lynn Holevinski, Elena Schiopu, Gary Freed, Cem Akin, Lili Zhao

Research output: Contribution to journalArticlepeer-review


Background: There is a lack of data regarding how the Delta variant of coronavirus disease 2019 (COVID-19) has impacted the effectiveness of the BNT162b2 (Pfizer-BioNTech), mRNA-1273 (Moderna), and Ad26.COV2.S (Johnson & Johnson-Janssen) vaccines at preventing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and COVID-19 hospitalization. Methods: We compared the effectiveness of the three vaccines during the pre- and post-Delta variant period (before and after 1 July 2021) in a large cohort of vaccinated and unvaccinated patients in the Michigan Medicine healthcare system. We assessed vaccine effectiveness (VE) using 2 analyses: an inverse propensity weighted (IPW) Kaplan-Meier (KM) analysis based on time from vaccination, and a Cox model based on calendar time with vaccination as a time-varying covariate. Results: Compared to Ad26.COV2.S recipients, the risk of hospitalization for COVID-19 in the post-Delta variant period was lower for BNT162b2 recipients (hazard ratio [HR] = 0.37; 95% confidence interval [CI]: [.14-.98]; P = .05) and mRNA-1273 recipients (HR = 0.21; 95% CI: [.07-.64]; P = .006). Recipients of the mRNA-1273 vaccine had a lower risk of SARS-CoV-2 infection than Ad26.COV2.S recipients (HR = 0.6; 95% CI: [.43-.83]; P = .003) and BNT162b2 recipients (HR = 0.64; 95% CI: [.54-.76]; P < .001). After 1 July, efficacy against SARS-CoV-2 infection declined for Ad26.COV2.S recipients (VE = 76% before; VE = 49% after; P = .02), BNT162b2 recipients (VE = 87% before; VE = 52% after; P < .001), and mRNA-1273 recipients (VE = 92% before; VE = 70% after; P < .001). Waning immunity and the Delta variant contributed independently and significantly to this decline. Conclusions: Although there is a substantial decline in effectiveness, the approved COVID-19 vaccines remain effective against infection and hospitalization due to the Delta variant. The mRNA-based vaccines are more effective than the Ad26.COV2.S vaccine.

Original languageEnglish (US)
Pages (from-to)E623-E629
JournalClinical Infectious Diseases
Issue number1
StatePublished - Jul 1 2022
Externally publishedYes


  • comparative effectiveness
  • COVID-19
  • COVID-19 vaccines
  • Delta variant
  • waning immunity

ASJC Scopus subject areas

  • Microbiology (medical)
  • Infectious Diseases


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