New Delhi, Apr 24: The health ministry has begun a probe into the deaths of four children who had received a measles vaccine in Thiruvallur district of Tamil Nadu.

The children died yesterday after receiving the vaccine manufactured by the Hyderabad-based Indian Immunologicals, a subsidiary of the National Dairy Development Board.

Health ministry sources said samples of the vaccine had been sent to the Central Drugs Laboratory at Kasauli, and all states asked to stop using the vaccine until the probe was complete.

The investigation team, asked by the ministry to visit the site today, will assess the quality of the vaccine and find out if it was kept at the requisite low temperature and handled appropriately before being administered to children.

A senior Indian Immunologicals official said the company had supplied several thousand vials from the same batch of the vaccine to health centres across the state. Each vial contained five doses of the vaccine.

Each batch of the vaccine is made up of about 50,000 vials, the official said. Sources said the government had earlier ordered several million units of the vaccine.