Vaccines for malaria pose deadly threat

Robin McKie, science editor
Sunday December 30, 2001
The Observer

Vaccines against malaria could trigger a deadly biological 'arms race' 
between nature and mankind. New forms of the disease, even more deadly 
than present versions, would be released with devastating consequences.

The warning has been issued by Edinburgh University researchers who 
think the first vaccines against the world's deadliest infectious 
illness could rebound unexpectedly on humanity.

'We are certainly not saying malaria research should be halted but we do 
warn researchers that they should realise vaccines could have 
unexpected, and very worrying, medium-term side effects,' said Professor 
Andrew Read, of Edinburgh's Institute of Cell, Animal and Population 
Biology.

'Everything would look good at first, with infection rates dropping. 
Then, in a few decades, new hyper-pathogenic strains could hit 
unprotected populations.'

A vaccine against malaria is one of the holy grails of modern medicine. 
The disease claims more than a million lives a year, most of them 
children in the Third World.

The disease is caused by a parasite spread by mosquitoes, which infects 
and destroys red blood cells. Efforts to create effective vaccines 
against malaria have been bedevilled because the parasite is a far more 
complex entity than a bacterium or virus. It exists in many different 
strains, and is constantly evolving into new versions.

Nevertheless, researchers have begun to make progress, and last year 
clinical trials of several different vaccines were launched. 'Early 
results have been encouraging - but they also indicate a malaria vaccine 
is unlikely ever to provide total protection,' said Read. 'The parasite 
is too complex for that.

'For example, one vaccine that went through clinical trials was found to 
reduce malaria infections rates by a third in a group of volunteers, 
compared with a similar group that was given no vaccine.'

It is this type of imperfect protection that could lead to the creation 
of deadlier strains of malaria, say the Edinburgh scientists.

They point out that virulent strains of malaria parasite normally die 
off almost as soon as they are created - because they kill off their 
human hosts. But once individuals start getting protection from 
vaccines, these super-strains would start to flourish. Inoculated 
individuals would act as breeding centres for super- parasites; 
mosquitoes would pick them up and spread them to other people.

'That would be fine if everyone in the world was given the vaccine, but 
that is extremely unlikely to happen,' said Read. 'Inevitably, a great 
many people will remain unvaccinated to begin with and will then become 
infected with the new super- strains - with deadly consequences.

'In other words, we shall have two sets of people - the protected, and 
those made especially vulnerable and liable to succumb to malaria. One 
lot will benefit at the expense of others.'

A parallel of this scenario has unfolded in Britain - with chickens. 
Poultry often become infected with Marek's disease, which causes tumours 
and costs farmers billions of pounds a year worldwide.

Initially, the disease caused less than 30 per cent fatalities in 
infected batteries. Then, in the Sixties, a vaccine was launched. Since 
then the percentage killed by the Marek's virus has risen to 100 per 
cent. Unless broods are given vaccines they can be wiped out when an 
outbreak occurs.

'The vaccine was probably the cause of this situation,' said Read. 
'Unless we are careful, we may see a similar effect with malaria and 
human beings. We are in danger of creating populations that are 
protected at the expense of other populations.

'It is a very disturbing ethical issue, and we are going to have think 
very carefully how we deal with its consequences.'