Breakthrough infection with SARS-CoV-2 delta variant in old-age homes in a Southern District of Kerala, India

Abstract

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.