Neutralising antibody levels waned after six months in those who were fully vaccinated against the coronavirus with Covishield, Covaxin and a mix of both — Covishield as the first dose and Covaxin as the second dose — in the context of the Omicron variant, a study done by the National Institute of Virology (NIV) in Pune has indicated.

The heterologous vaccination regimen of administering the first dose of Covishield, followed by the second dose of Covaxin had given a very good neutralising response against Delta and other Variants of Concern, Dr Pragya Yadav, a scientist at the NIV, said.

The study involved three cohorts — a heterologous group with 18 individuals who were inadvertently administered the first dose of Covishield and the second dose of Covaxin in Uttar Pradesh and two groups comprising 40 individuals each receiving two doses of homologous Covishield or Covaxin.

"All the three groups were closely monitored. When we analysed the cohorts in June last year, the heterologous vaccination regimen of administering the first dose of Covisheid, followed by the second dose of Covaxin showed a very good neutralising antibody response against Delta and other Variants of Concern, as compared to the two other cohorts," Yadav said.

The study findings have been published in the Journal of Travel Medicine.

‘Devising an innovative vaccination strategy’

"The gradual shift of VoCs from Delta to Delta-sub-lineage to Omicron, along with the observed waning of immunity post six months of vaccination, has prompted discourses around devising an innovative vaccination strategy. The present investigation findings contribute meaningfully to such discussions. Regardless of the findings of this study, longitudinal monitoring for breakthrough infections should remain a part of any surveillance system," the study stated.

India began administering the precautionary doses of the Covid-19 vaccines to the healthcare and frontline workers and those aged 60 years and above with comorbidities from January 10. The Union health ministry removed the comorbidity clause recently, making everyone aged above 60 years eligible for the precautionary dose of the Covid vaccines. The vaccination of children aged 12-14 years started from March 16.

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