Pivotal studies supporting the efficacy of rotavirus vaccines developed by Merck & Co and GlaxoSmithKline have been published in the January 4 issue of the New England Journal of Medicine.

A trial of Merck’s Rotateq candidate in 70,000 infants, called REST, found that the vaccine prevented 98% of severe cases of rotavirus gastroenteritis caused by serotypes targeted by the vaccine. The data has been reviewed by a US Food and Drug Administration (FDA) advisory committee which recommended approval of Rotateq at a meeting last month.

Meanwhile, the 63,000-infant trial of GSK’s Rotarix vaccine found that it prevented 85% to 100% of rotavirus cases, depending on the severity of the disease. Rotarix is already on the market in Mexico as GSK has focused on securing approval first in countries with the greatest need for vaccination.

One of the key considerations at the advisory panel meeting was the rate of a side effect called intussusception, a severe twisting of the bowel that led to the only previously approved rotavirus vaccine - Wyeth's RotaShield - being withdrawn from the market in 1999.

The published account of REST found no difference between Rotateq and placebo groups with regard to the rate of intussusception after a year’s follow-up. Similarly, GSK’s vaccine was not associated with any increased risk of the side effect.

Rotavirus is the most common cause of severe dehydrating gastroenteritis in infants and young children. Merck’s vaccine targets five strains of rotavirus - G1, G2, G3, G4 and P1 - responsible for more than 90% of rotavirus disease around the world. GSK says Rotarix tackles four strains, including the globally emerging G9P[8].

Worldwide, rotavirus causes more than two million hospitalisations and nearly 500,000 deaths each year.

Merck submitted a Biologics License Application in the USA for Rotateq in April 2005, while partner Sanofi Pasteur MSD filed the product in Europe in the same month. Merck says it is planning to conduct clinical studies this year to evaluate the use of Rotateq in the developing world.

GSK said that since the Mexican launch Rotarix has been licensed in 12 additional Latin American countries and its first markets in Asia – Philippines and Singapore. Approval in Europe is expected in February, although GSK has not yet filed Rotarix in the USA.