"We have formed a high-level committee to investigate the matter, but initial probe showed that there was nothing wrong with the vaccines. It is possible that the children were suffering from other ailments," Health Secretary M Nagaraju told reporters here.
Three children have died and five others fell sick in different parts of West Tripura district during the past three days, according to official reports.
Media reports said the deaths took place after an immunisation drive against Japanese Encephalitis (JE) in the area.
He said the committee would submit its report within a week.
Health Minister Badal Chowdhury said the Union Health and Family Welfare Ministry had decided to launch a vaccination drive in 27 affected districts including West Tripura district in the country.
The vaccination drive for the children with 1 to 15 years as the main target group started in Tripura on May 23 last and over 2,10,000 were administered vaccines already.