A recent case report suggests that the meningitis bacteria can change serotypes, mutating, for example, from type C to type B or vice versa.

This case report involved a 16 year old girl who died of fulminating type B meningitis. Unsure of how she may have contracted the disease, doctors examined all her close contacts. Her boyfriend was found to have meningitis C, and close examination of the two viruses isolated from both the girl and her boyfriend showed them to be genetically identical in every way except for one gene fragment.

Although the possibility of mutation has been noted in in vitro studies, this is one of the first actual live cases where the switch has been observed.

The authors suggest that the meningitis virus can switch subgroups extraordinarily rapidly, within a matter of days, and because of this, call into question the wisdom of mass immunisation against a single subgroup of the bacteria, as Britain is now doing against the C strain of the meningococcal bacteria. Wiping out one strain of bacteria might simply cause the others to flourish, they say.

At present, there is no vaccine against the B strain, which kills more people than the C strain (N Engl J Med, 2000; 342: 219-20).