A rare strain of meningitis has claimed the lives of four Britons and struck 20 others after they visited the holy Muslim cities of Mecca and Medina.

The unprecedented spate of fatalities among British pilgrims travelling to the Hajj in Saudi Arabia has led to calls for the Department of Health to review its advice on vaccination.

The victims have all been hit by the uncommon W135 variant of meningococcal meningitis, which accounts for about 2 per cent of the 2,500 cases of the disease each year. Another two British pilgrims were struck by a different strain.

About 20,000 Britons attend the annual gathering in Mecca but it is the first time such large numbers have been hit by the bug. There have also been 14 confirmed cases including four deaths in France - 11 caused by the W135 strain - and two non-fatal cases in the Netherlands.

Saudi Arabia requires pilgrims travelling from Britain to be vaccinated against the A and C strains of meningitis, but these do not provide protection against W135. There is a vaccine against the W135 strain but the Department of Health does not make it routinely available because of the rarity of the strain in Britain.

A spokeswoman for the department said: "Because it is very scarce in this country we don't keep great amounts of the vaccine. But after any outbreak like this the department does look at the processes in place to see how it can be prevented."

She advised pilgrims who developed flu-like symptoms, such as fever, headache, stiff neck and a rash that does not fade under pressure - a sign of septicaemia - to consult their GP immediately. Antibiotics have been offered to relatives and close friends of those affected.

The family of one of the victims is considering legal action against King George's Hospital in Goodmayes, Essex, whom they accuse of being negligent in failing to diagnose the symptoms.

Rashida Bunglawala, from Ilford, who was 56, died on 4 April three hours after being discharged from the hospital still complaining of a severe headache and pain. She had been in the country two days since returning from Saudi Arabia.

Her son, Inayat, one of six children, said: "Doctors should warn all pilgrims intending to travel to take out a vaccination against this strain W135 which is very virulent and very lethal."

The final casualty count may be much higher. Although the Hajj finished more than four weeks ago, many Britons have delayed their return to stay on continue their religious observances.

The W135 strain of meningitis is common in sub-Saharan Africa and it is likely that the infected Britons contracted it from fellow pilgrims in the crowded and confined spaces of Mecca and Medina.

The UK Public Laboratory Health Service said the close proximity of hundreds of thousands of people from all over the world in often unhygienic surroundings provided fertile conditions for the disease to spread. "If strains of bacteria are circulating in the same place then that gives the organism potential to transmit more widely," a spokesman said.

Dr Mohammed Shafi, a microbiologist at Central Middlesex Hospital, said the Government should consider improving the availability of the vaccine for W135.

The Saudi Arabian embassy declined to comment.