A Self-Reported Survey-Based Evaluation of the Real-World Effectiveness of Non-mRNA COVID-19 Vaccines During the Second Pandemic Wave in India.

Introduction Breakthrough infections (BIs), defined as SARS-CoV-2 infections occurring in fully vaccinated individuals, provide crucial insights into vaccine effectiveness. Data on BIs after non-mRNA vaccines remains limited. Aim This study aimed to evaluate the incidence, characteristics, and risk factors associated with COVID-19 BIs in individuals vaccinated with Covishield (Serum Institute of India Pvt. Ltd.) and Covaxin (Bharat Biotech) in India. Methods A survey was conducted from June 1 to September 15, 2021, via Google Forms, disseminated through social media and email. After excluding duplicates and incomplete responses, 5248 were analyzed. Statistical analyses, including chi-squared tests and logistic regression, assessed the risk factors for BIs and their severity. Results Among 5248 respondents, 405 (12.9%) reported BIs. Age >60 years was associated with a higher BI rate (p<0.00001), greater severity (p<0.0001), and higher mortality (p<0.0001). Mortality was higher in men (5.67%) than in women (1.37%; p=0.005). BI rates were similar between Covishield (12.7%) and Covaxin (13.9%) recipients (p=0.4). Longer interdose intervals (5-12 weeks) were associated with lower BI rates (p=0.005). Healthcare workers had higher BI rates (p<0.008) but lower severity (p=0.009) and mortality (0.64% vs. 6.76%; p<0.001). Severe BIs were more common in individuals with comorbidities (p<0.0002). Mortality rate was significantly lower in fully vaccinated individuals (2.29%) compared to incompletely vaccinated individuals (6.22%; p=0.016). Conclusions Full vaccination reduced severe disease and mortality. Older age, comorbidities, and occupational exposure were key risk factors. Despite higher exposure, healthcare workers had lower infection severity and mortality. These findings highlight the importance of optimized vaccine dosing, booster doses for high-risk groups, and continued public health measures.