Which COVID‑19 vaccine, Covishield (ChAdOx1 nCoV-19) or Covaxin (BBV152), is more effective?

Covishield Demonstrates Superior Effectiveness Compared to Covaxin

Based on the highest-quality comparative evidence, Covishield (ChAdOx1 nCoV-19) is more effective than Covaxin (BBV152) for preventing COVID-19 infection and severe disease, with vaccine effectiveness of 85% versus 71% against severe COVID-19, and significantly higher antibody responses across multiple studies. 1

Vaccine Effectiveness Against Severe COVID-19

The most robust comparative data comes from a multi-centric hospital-based case-control study conducted during India's Delta variant wave in 2021:

• Covishield achieved 85% effectiveness (95% CI: 79-89%) against severe COVID-19 after complete vaccination (2 doses ≥14 days apart) 1
• Covaxin achieved 71% effectiveness (95% CI: 57-81%) against severe COVID-19 after complete vaccination 1
• Both vaccines demonstrated similar effectiveness against the Delta variant and its sub-lineages, which was the dominant strain during India's devastating second wave 1

A separate hospital-based study in Odisha confirmed these findings with slightly different estimates:

• Covishield: 79.0% effectiveness (95% CI: 65.4-87.2%) after two doses 2
• Covaxin: 74.0% effectiveness (95% CI: 50.5-86.0%) after two doses 2

Immunogenicity and Antibody Response

The most definitive head-to-head immunogenicity comparison comes from a 2024 multicentre study across four Indian sites, which demonstrated Covishield's clear superiority in antibody generation:

In Seronegative Individuals (No Prior COVID-19 Infection):

• Covishield seroconversion rate: 98.3% versus Covaxin: 74.4% (p < 0.0001) 3
• Covishield anti-spike antibody GMT: 1272.1 BAU/ml versus Covaxin: 75.4 BAU/ml (p < 0.0001) 3

In Seropositive Individuals (Prior COVID-19 Infection):

• Covishield seroconversion rate: 91.7% versus Covaxin: 66.9% (p < 0.0001) 3
• Covishield anti-spike antibody GMT: 2089.07 BAU/ml versus Covaxin: 585.7 BAU/ml (p < 0.0001) 3

Neutralizing Antibody Responses:

• Covishield elicited higher surrogate neutralizing antibody responses against variants-of-concern including Delta and Omicron compared to Covaxin 3
• This superiority was consistent in both seronegative and seropositive individuals 3

Cellular Immune Response

Covishield demonstrated broader T-cell activation:

• Covishield elicited both CD4+ and CD8+ spike-specific cytokine-producing T cells in seronegative individuals 3
• Covaxin elicited mainly CD4+ spike-specific T cells, with less robust CD8+ responses 3
• Neither vaccine showed significant post-vaccination expansion of spike-specific T cells in seropositive individuals 3

A separate immunogenicity study confirmed sustained immune responses:

• Covaxin showed robust T-cell responses (31% at 1 month post-first dose versus 96% at 6 months post-second dose), justifying the utility of the second dose 4
• Covishield demonstrated persistent IgG and neutralizing antibody responses along with IgG+ B cells and memory B cells at 6 months post-second dose 4

Optimal Dosing Intervals

The effectiveness of both vaccines is significantly influenced by the interval between doses:

• Covishield: Maximum effectiveness (94%, 95% CI: 86-97%) achieved with 6-8 weeks between doses 1
• Covaxin: Maximum effectiveness (93%, 95% CI: 34-99%) achieved with 6-8 weeks between doses 1
• Among people living with HIV, a 4-6 week interval between doses provided higher vaccine effectiveness compared to longer intervals 5

Special Population Considerations

Kidney Transplant Recipients:

• Covishield showed significantly higher antibody response compared to Covaxin (aOR 5.04,95% CI: 1.56-16.22; p = 0.007) 6
• Diabetes at vaccination was associated with poorer antibody response (aOR 0.31,95% CI: 0.10-0.90; p = 0.032) 6
• Graft dysfunction at baseline was associated with poorer antibody response 6

People Living with HIV:

• Covaxin effectiveness: 73.4% (95% CI: 44.3-87.3%) 5
• Covishield effectiveness: 63.8% (95% CI: 39.3-79.2%) 5
• Participants with baseline CD4 count >350 had greater protection (53.4%, 95% CI: 19.6-75.3) 5

Safety Profile

Both vaccines demonstrated acceptable safety profiles, though Covishield produced more frequent adverse events:

• Covishield: 85.3% of recipients reported at least one adverse reaction, most commonly injection-site pain, fever, fatigue, and malaise 7
• Covaxin: 17% reported adverse reactions, most commonly injection-site pain, tenderness, and fatigue 7
• Adverse events were more common after the first dose (adjusted OR = 3.39,95% CI: 2.24-5.11, p < 0.001) 7
• Women experienced more adverse events than men (adjusted OR = 1.68,95% CI: 1.24-2.29, p = 0.001) 7
• No serious adverse events were reported with either vaccine 7

Clinical Implications and Recommendations

For general population vaccination, Covishield should be the preferred choice based on:

1. Higher vaccine effectiveness against severe COVID-19 (85% vs 71%) 1
2. Significantly superior antibody responses (17-fold higher GMT in seronegative individuals) 3
3. Broader cellular immune activation (both CD4+ and CD8+ T cells) 3
4. Better neutralizing antibody responses against variants-of-concern 3

For immunocompromised populations (transplant recipients, cancer patients):

• Covishield demonstrates superior immunogenicity and should be strongly preferred 6
• Ensure CD4 counts >350 in HIV-positive patients before vaccination 5
• Consider timing vaccination relative to immunosuppressive therapy 6

For patients concerned about adverse events:

• Covaxin produces fewer reactogenic symptoms (17% vs 85.3%) and may be preferred in individuals with low tolerance for post-vaccination symptoms 7
• However, the clinical significance of these mild-to-moderate adverse events must be weighed against the substantially lower antibody responses 7, 3

Common Pitfalls to Avoid

• Do not assume equivalent effectiveness based on both vaccines being approved for use; the evidence clearly demonstrates Covishield's superiority in antibody generation and clinical effectiveness 1, 3
• Do not delay the second dose beyond 8 weeks for either vaccine, as effectiveness peaks at 6-8 weeks and declines with longer intervals 1
• Do not withhold vaccination in immunocompromised patients due to concerns about reduced response; even suboptimal antibody responses provide meaningful protection against severe disease 6, 5
• Do not dismiss Covaxin entirely; it remains effective (71% against severe COVID-19) and may be appropriate when Covishield is unavailable or contraindicated 1