Eight children who received Merck & Co's RotaTeq vaccine developed a rare blood-vessel disorder that can lead to aneurysms and heart attacks, and the company is adding a warning to its label.

Merck is changing the label on its rotavirus vaccine RotaTeq after it noted five cases of Kawasaki disease in clinical trials and three reports of the illness since the vaccine was introduced in February 2006, the US Food and Drug Administration has announced. About 4,000 children in the USA, about 80% under age five, develop Kawasaki disease each year and the cause is unknown.

About six million doses of the vaccine had been administered in the USA and the agency pointed out that “there is not a known cause and effect relationship between receiving RotaTeq, or any other vaccine, and the occurrence of Kawasaki disease. The cases reported to date are not more frequent than what could be expected to occur by coincidence”. The FDA added that doctors and parents “should remain confident in using RotaTeq”.

RotaTeq is an oral vaccine used to prevent rotavirus, a common cause of severe diarrhoea and hospitalisation in infants. The virus is a major killer of children in developing countries, but deaths in the USA from the disease, for which RotaTeq is the only approved treatment, are rare.

Merck changed the label on RotaTeq in February to note that 28 cases of a potentially life-threatening twisting of the intestines (intussusception) in infants were reported during the product's first year on the market. At the time, the FDA noted that the data did not suggest a link between the vaccine and the condition.