A life-threatening form of pneumonia that affects children is rising rapidly in Britain. Cases of the pneumonia, known as serotype 1, have risen tenfold in a decade.

This severe form of pneumonia infects the lining of the lungs called the pleura, making it hard to breathe. The cause of the increase is unknown, but experts fear a vaccine could be contributing.

A vaccine against pneumococcal disease called Prevenar, introduced in 2006, could be fuelling the rise. The vaccine is given at two, four and 13 months. There are more than 90 known strains of the bacterium that causes pneumonia, and when one is eliminated by the vaccine, it creates an opportunity for another to take its place. In the U.S., where Prevenar was introduced in 2000, researchers have reported an emergence of "sero-replacement" disease -- types of pneumonia not covered by the vaccine.