Genomic analysis of Varicella zoster virus strains during an outbreak with atypical clinical presentations in Biswanath district of Assam, India.

Chickenpox, caused by the Varicella Zoster Virus (VZV), presents as varicella (chickenpox) during primary infection and as herpes zoster (shingles) upon reactivation. With a high infectivity rate and transmission through airborne droplets and contact, VZV poses a significant public health challenge. While the disease is self-limiting, complications such as encephalitis and pneumonia can occur, particularly in unimmunized individuals and those with weakened immune systems. The introduction of varicella vaccination has significantly reduced incidence and complications in countries with universal vaccination programs, but India is yet to incorporate this vaccine into its national immunization schedule. In June 2023, an outbreak of varicella was reported in Biswanath district, Assam, affecting 18 individuals. The outbreak highlighted the impact of factors such as overcrowding, poor ventilation, and inadequate medical intervention. Clinical symptoms included fever, vesicular rash, and severe abdominal pain, with three fatalities linked to severe complications. Molecular and serological investigations confirmed VZV infection in the cases, and whole genome sequencing (WGS) identified the strain as belonging to Clade 5. Phylogenetic analysis revealed the strain's similarity to other Indian VZV sequences, aligning with the established VZV clade nomenclature. The outbreak investigation underscored the importance of timely medical intervention and effective vaccination strategies. Enhanced surveillance, community awareness, and a coordinated response involving various health stakeholders are crucial for managing varicella outbreaks and improving vaccination coverage. This study represents the first comprehensive genomic analysis of VZV from Northeast India, providing valuable insights into the strain circulation and reinforcing the need for vaccination and preventive measures.