Measles eradication thought to be a feasible target

Press, 9 June 1982, Page 13

Measles eradication thought to be a feasible target

From the "Economist." London American medical experts, at the International Measles Symposium held in Washington D.C. in March, triumphantly declared that they were well on their way to eradicating measles by this (October, a target originallyset in 1978.

Only 3000 cases of measles were reported in the United States in 1981. as against 424.000 in 1961. The key to the American success has been the drive to immunise all children when they first enter school: 96 per cent have now been vaccinated. Also, the measles vaccine itself has improved. It is now highly effective (up to 95 per cent) and requires onlyone injection — no boosters.

This success story has raised hopes that measles could be eradicated worldwide — as smallpox has been. The World Health Organisation agrees this is a feasible target.

W.H.O. also wants to see the immunisation of all children against five other diseases — including whooping 'cough and poliomyelitis — while recognising that their total eradication is not yet possible. Unfortunately, even with measles, there are enormous problems.

i One is a lack of commitj ment — even in some deyeli oped countries. Britain and France, for example, simply

do not consider measles a serious disease, vaccination levels of pre-school children are only 20-50 per cent. This is arguably silly: 8 per cent of measles cases develop complications such as ear infections; 1 per cent develop pneumonia; 0.1 per cent devastating brain infections;. and 0.01 per cent die.

In Britain last year, nearly 53.000 cases of measles were reported. In developing countries. measles still kills over a million children. There are also technical problems. Measles (and also oral polio) vaccines must be kept refrigerated to remain active. This is difficult to ensure in developing countries.

One of the reasons behind the success in obliterating smallpox was that the vaccine was freeze-dried and did not lose its efficacv in heat.

The efficacy of the measles vaccine is optimum when given to infants aged 13-15 months. In younger children, antibodies tsp measles passed on by their mothers can interfere with immunisation. But children in developing countries are susceptible to measles very early on — at the age of six months.

Vaccines against the other diseases on W.H.O.'s target list are not so convenient or effective as the measles vaccine.

The whooping cough vac-

cine. using whole bacteria called Bordetella pertussis, has efficacy rates of 70 per cent to 90 per cent (and requires four doses).

Dr Paul Fine and Dr Jacqueline' Clarkson of the London School of Hygiene and Tropical Medicine have recently pointed out that the present' whooping cough vaccine- may not even protect against infection — but just prevent the infection from developing into a fully fledged disease. If correct, that does not bode well for any eventual eradication campaign. A search has been on for the last eight years to find a better vaccine. An alternative to using whole bacteria has now been found by scientists from Britain's Centre for Applied Microbiology and Research at Porton Down. They have isolated two components on the surface of the offending bug that could be used to protect against whooping cough. The vaccine should be on the market by 1987. Japan reportedly already has a similar product in clinical trial.

The battle against polio in developed countries improved with the introduction of the oral Sabin vaccine, in the earlv 19695.

But it is thought that viruses found in the gut of inhabitants of developing countries may hinder the

activity of the oral vaccine. These countries might have to return to the older Salk vaccine, which is expensive.

Again, new research maycome to the rescue. Institut Merieux of France has developed a method of producing the Salk vaccine more cheaply by growing the host cells needed for it on small beads. The new Salk is now being tested in trials in the Netherlands and the United States.

Unfortunately, even if the new Salk passes its trials with flying colours, a hitch will remain. The oral Sabin vaccine is based on live polio viruses which can spread from the recently immunised to others who come in contact with them.

But Salk is based on dead viruses. So higher immunisation rates would be needed with Salk.

These are just some of the .problems faced by immunisation campaigns against measles, whooping cough and polio. Critics of immunisation schemes are quick to point out another — expense. Dr Ralph Henderson of W.H.O. reckons this is a “non-issue": it would cost the developing countries (not including China) only $3OO million a year to immunise 100 million children against all three diseases plus diphtheria. tetanus and tuberculosis.