A study conducted by the National Institute of Virology (NIV) in Pune has claimed that the antibody level of the double dose of the Covid vaccine waned after six months with regard to the Omicron variant.
However, the heterologous vaccination regimen of administering the first dose of Covishield, followed by the second dose of Covaxin has given a neutralising response against Delta and other variants of Concern, Dr Pragya Yadav, a scientist at the NIV, said.
The study findings were published in the Journal of Travel Medicine recently. 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 the other two groups comprising 40 individuals each receiving two doses of homologous Covishield or Covaxin.
The study found that those who were inadvertently administered mixed doses of Covid vaccines showed a very good neutralising antibody response against Delta and other Variants of Concern.
However, with regard to the Omicron variant of coronavirus, there was a reduction seen in neutralizing antibody levels in all cohorts (Covishield + Covaxin; Covaxin +Covaxin and Covishield + Covishield).
“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 precaution 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 precaution dose of the Covid vaccines.