Occurrence of COVID-19 in priority groups receiving ChAdOx1 nCoV-19 coronavirus vaccine (recombinant): a preliminary analysis from north India
Authors: Kaur Upinder , Bala Sapna , Ojha Bisweswar , Jaiswal Sumit , Kansal Sangeeta , Chakrabarti Sankha Shubhra 
Published: August 2021

Background: In randomized controlled settings, vaccine efficacy close to 70% against symptomatic COVID-19 has been demonstrated by the ChAdOx1 nCoV-19 vaccine which is a recombinant chimpanzee adenovirus based vaccine expressing the SARS-CoV-2 spike protein. Post approval studies are however necessary to validate the findings in the real world.Methods: A prospective observational study is being conducted in a tertiary hospital of north India since 5th February 2021 with the primary objective of determining safety of COVID-19 vaccines and the secondary objective of assessing the rate of occurrence of COVID-19 in vaccinated group. High risk group comprising health care workers, other frontline workers (police, sanitary workers etc) and elderly citizens who were initially focus groups for vaccine roll-out in India, were enrolled in the study. The study included all vaccine recipients who provided consent and were enrolled at the time of receiving the first or second dose of COVISHIELD vaccine, and followed up telephonically.Results: Among 1650 enrolled vaccine recipients, 1500 participants of the study (Female/Male: 472/1028; mean age 38.8 years) completed at least 2 months of follow-up, after the second dose. The common comorbidities in study participants were hypertension (170, 11.3%), diabetes (142, 9.5%), and hypothyroidism (54, 3.6%). Of those who received a single dose of vaccine (n=65), laboratory confirmed SARS-CoV-2 infection was observed in 27 individuals (41.5%) and 3 were suspects. Severity wise, infections were mild in 21 out of 30 (70%) cases, moderate in five (16.7%) and severe in two (6.7%). Of those who received both doses of vaccine (n=1435), 388 were diagnosed as confirmed or suspect cases of SARS-CoV-2 infection. Of these 388, RT-PCR positivity was seen in 271 (18.9%) individuals, 82 (5.7%) were labelled as ‘suspects’ and 35 (2.4%) were RT-PCR negative suspects. Severity wise, majority of SARS-CoV-2 infections were ‘mild’ (331/388, 85.3%), followed by ‘moderate’ (33/388, 8.5%) and ‘severe’ (6/388, 1.5%). 404 out of the 1500 total participants were doctors including consultant/teaching faculty, resident doctors, and those in general practice. Among the 377 doctors who received both doses of vaccine, 160 were diagnosed as confirmed or suspect cases of SARS-CoV-2 infection. Of these, 131 (34.7%), 17 (4.5%) and 12 (3.2%) were laboratory confirmed cases, ‘suspects’ and RT-PCR negative suspects respectively. The infection was asymptomatic, ‘mild’, ‘moderate’ and ‘severe’ in 9 (5.6%), 130 (81.3%), 16 (10%) and 5 (3.1%) respectively. Breakthrough infections occurring at > 14 days after receiving the second dose were seen in 148 doctors who received both doses (39.2%), or 119 doctors (31.6%) if only laboratory confirmed cases were considered. Four deaths occurred in the study participants during the study period, two in partially vaccinated group and two in fully vaccinated group. Two of these participants, both in partially vaccinated group had developed SARS-CoV-2 infection during their follow-up.Conclusion: The disproportionately high occurrence of SARS-CoV-2 infection and COVID-19 in priority vaccinated groups in our study can be explained to some extent by the existence of variants such as the delta which might have escaped the vaccine generated immune protection. Despite the high incidence, the severity of COVID-19 was observed to be low. Since the ongoing study was primarily focused on adverse events following immunization (AEFIs) and enrolled only vaccinated individuals, the secondary outcome results lack a control unvaccinated group. However, the result of this preliminary analysis necessitates vigorous research on the performance of vaccines against variants, optimal timing of vaccination, need for boosters, and also optimal timings of effectiveness studies to guide future vaccination policy.