Breakthrough Infection with SARS-CoV-2 Delta Variant in Old-Age Homes in a Southern District of Kerala, India

Background: The incidence of breakthrough infection with the emergence of new variants of concern of SARS?CoV?2 is posing a threat, and it is pertinent to understand the role of vaccines in protecting the elderly and people with comorbidities. Objective: The present study was undertaken to understand the natural history of SARS?CoV?2 infection in a closed cohort of the elderly population in an old?age home who have received two doses of COVID?19 vaccination. The study has also undertaken genomic sequencing to identify SARS?CoV?2 variants of concern from an academic perspective. Materials and Methods: A prospective observational study was conducted from March to August 2021 among residents of 11 old?age homes in Kerala who were vaccinated with 2 doses of the COVID?19 vaccine, from 2 weeks following vaccination. Samples with a threshold cycle value of <25 were subjected to targeted sequencing of the spike protein receptor?binding domain coding region. Results: Among the 479 vaccinated individuals, 86 (17.95%) turned positive during the follow?up period. The mean duration of symptoms was 3–5 days, and no hospitalization was required. A phylogenetic analysis of the nucleotide sequences from the samples indicated B.1.617.2 lineage representing the Delta strain. Conclusion: The evidence supports maximizing the vaccine coverage among vulnerable groups to prevent hospitalization and death rate on the verge of the emergence of new variants of SARS?CoV?2.