Study registration: *
Publication Singh C, Epidemiol Infect, 2021
Dates: 2021-04-01 to 2021-06-30
Funding: No specific funding (This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.)
Conflict of interest: no COI (Conflict of interest: None.)

Methods

Study design:Case-control
Description of participants: Adults aged 45 and up in a single centre in India
Inclusion criteria:
  • ≥45 years
  • a valid report (rapid antigen (Ag) or reverse transcriptase polymerase chain reaction (RT-PCR) for SARS-CoV-2
  • attending COVID dedicated flu clinic during the study period (cases) or tested negative in the previous 3 days (controls)
  • assessed from April to June 2021
  • at All India Institute of Medical Sciences (AIIMS), Patna, Bihar, India
  • only one participant from a family having multiple eligible participants (index-one) was considered.

Exclusion criteria:
  • Re-infected patients
  • family members of patients already included in the study
  • SARS CoV-2-negative controls with a history of COVID-19 or influenza-like illness (ILI) in the preceding 3 months from the day of data collection

Follow-up duration (months): 3.00
Vaccines:
  • 1 or 2 dose BBV152
  • 1 or 2 doses of ChAdOx or BBV152
  • 1 or 2 doses of ChAdOx
Variant description :
Variant name: Delta
Evidence: Indirect evidence (prevalence of variant in the population: 30 to 99%)
Documents
available

Protocol

NR

Statistical plan

No

Data-sharing stated: Unclear
Data accessibility: Author for correspondence: Bijit Biswas, E-mail: drbijitbiswas@gmail.com

General comment In addition to the published report, the supplementary material were used in data extraction and risk of bias assessment. Follow-up time was estimated using the date of start of vaccination for the elderly and individuals aged above 45 years with comorbidities (March 1, 2021); however, for healthcare workers (6% of the study sample) and front-line workers it was earlier (January 16, 2021).

The main concerns were uncontrolled confounding, adjustment for a variable potentially on the causal pathway, selection bias and potential differential misclassification of vaccination status.