Merck and Sanofi Pasteur are ending their partnership, begun in 1994, to market the drugmakers' vaccines in Europe.
The joint venture currently sells 25 vaccines in 19 European countries, including Merck & Co.'s shingles vaccine Zostavax and Sanofi Pasteur's influenza vaccine Intanza.
In a joint statement, they said the 50/50 joint venture has had commercial and public health success, but that it's "in our best interests to manage our vaccine product portfolios independently."
Merck, of Kenilworth, New Jersey, and Sanofi Pasteur, part of France's Sanofi SA, are among the world's top vaccine makers. They compete on many vaccines, including ones for most pediatric illnesses, pneumonia and related bacterial infections, and cancer-causing human papilloma virus.
The companies expect to complete the separation by year's end and are working out terms.