What is the efficacy of Covishield (Oxford-AstraZeneca vaccine) and Covaxin (Bharat Biotech vaccine) in preventing COVID-19?

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Last updated: January 27, 2026 • View editorial policy

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Efficacy of Covishield and Covaxin Against COVID-19

Both Covishield and Covaxin demonstrate substantial efficacy against COVID-19, with Covishield showing approximately 85% effectiveness and Covaxin showing 71% effectiveness against severe disease during the Delta variant wave, based on the highest quality real-world evidence from India. 1

Covishield (Oxford-AstraZeneca) Efficacy

Covishield demonstrates robust protection against COVID-19 with particularly high effectiveness against severe disease requiring hospitalization. 1

Overall Effectiveness

  • Complete vaccination (2 doses ≥14 days apart) provides 85% effectiveness (95% CI: 79-89%) against severe COVID-19 1
  • Single dose effectiveness is 49% (95% CI: 17-68%) 2
  • Two-dose effectiveness against any COVID-19 infection is 54% (95% CI: 27-71%) 2
  • Real-world vaccine effectiveness in healthcare workers showed 70% (95% CI: 61-77%) protection against breakthrough infections 3

Protection Against Severe Disease

  • 95% effectiveness (95% CI: 44-100%) against moderately severe disease requiring oxygen therapy 2
  • Hospitalization rates among fully vaccinated healthcare workers were extremely low (0.0016/100 person-days) with zero deaths reported 3

Optimal Dosing Interval

  • Highest effectiveness of 94% (95% CI: 86-97%) achieved when the interval between two doses is 6-8 weeks 1
  • This extended interval significantly improves immunogenicity compared to shorter intervals 1

Mechanism and Variant Coverage

  • Utilizes a recombinant, replication-deficient chimpanzee adenovirus vector (ChAdOx1) encoding the SARS-CoV-2 spike glycoprotein 4
  • Maintains similar effectiveness against the Delta variant and its sub-lineages 1
  • The adenovirus vector delivers DNA (not mRNA) for spike protein production without causing infection 4

Covaxin (BBV152) Efficacy

Covaxin, an inactivated whole-virion vaccine, provides strong protection against severe COVID-19 with potential advantages against future variants. 1, 5

Overall Effectiveness

  • Complete vaccination provides 71% effectiveness (95% CI: 57-81%) against severe COVID-19 1
  • Phase 3 trials demonstrated approximately 80% overall efficacy 5

Optimal Dosing Interval

  • Highest effectiveness of 93% (95% CI: 34-99%) when doses are administered 6-8 weeks apart 1
  • This extended interval maximizes immune response 1

Variant Coverage and Theoretical Advantages

  • Maintains effectiveness against Delta variant comparable to Covishield 1
  • Potential advantage for future variants: As an inactivated whole-virus vaccine, Covaxin generates antibodies against multiple viral epitopes, not just the spike protein 5
  • If spike protein mutations significantly alter Covishield's target, Covaxin may retain broader protective capacity 5

Enhanced Protection with Prior Infection

Individuals with previous COVID-19 infection who receive complete vaccination achieve superior protection. 3

  • Combined natural immunity plus full vaccination provides 88% effectiveness (95% CI: 80-93%) 3
  • This hybrid immunity offers the highest level of protection documented in real-world studies 3

Safety Profile

Both vaccines demonstrate excellent safety profiles with no severe adverse events reported in large healthcare worker cohorts. 3

  • No severe adverse events documented among 2,762 healthcare workers over 9 months of observation 3
  • Minor reactogenicity is expected but does not contraindicate vaccination 3

Critical Implementation Points

Vaccination Priority

  • Healthcare workers and high-risk populations should receive priority vaccination regardless of vaccine type 3, 1
  • Complete two-dose series is essential—partial vaccination provides substantially lower protection 2, 1

Timing Considerations

  • Allow 6-8 weeks between doses for optimal effectiveness with either vaccine 1
  • Full protection begins 14 days after the second dose 3, 1

Common Pitfall to Avoid

  • Do not delay the second dose beyond 8 weeks despite higher efficacy at 6-8 weeks, as prolonged intervals may leave individuals vulnerable during high transmission periods 1
  • Do not consider single-dose vaccination adequate—the difference between partial and complete vaccination is substantial (49% vs 85% for Covishield) 2, 1

References

1
Research

Effectiveness of BBV152/Covaxin and AZD1222/Covishield vaccines against severe COVID-19 and B.1.617.2/Delta variant in India, 2021: a multi-centric hospital-based case-control study.

International journal of infectious diseases : IJID : official publication of the International Society for Infectious Diseases, 2022

4
Guideline

Mechanism of Action and Efficacy of Covishield Vaccine

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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