Parents who may be concerned by a scare over the side effects of the whooping cough vaccine will be reassured by a new study involving thousands of children.
The Department of Health advice that babies should be vaccinated against whooping cough (pertussis) at the age of two, three and four months has been questioned by some scientists who have suggested a link with asthma and allergies.
But the latest research published in Bristol shows no association between the vaccine and asthma or allergy in later childhood. It is one of the most comprehensive surveys to be published on the subject.
The findings are based on data collected by the University of Bristol's Children of the 90s project, also known as the Avon Longitudinal Study of Parents and Children (ALSPAC).
In recent decades the prevalence of allergic diseases including hayfever, asthma and eczema has risen in the industrialised world - leading to speculation that vaccination in early childhood may be one cause.
The possible link between pertussis vaccine and asthma and atopy (allergies) was first suggested in 1994, and again three years later by a study of 1200 children in New Zealand.
The Bristol researchers went through the immunisation records of 13,811 children - of whom 94.9 (13,109) per cent had been fully immunised. 340 hadn't been immunised at all, while others had received some of the vaccinations.
By the age of 91 months, 20.1 per cent of the children had been diagnosed with asthma at some time by a doctor.
At the age of seven, 20.5 per cent showed an allergic reaction to a skin prick test.
In 9.8 per cent of cases, parents had reported periods of wheezing in their children, with whistling on the chest in the past year.
The researchers found whether or not the child has been fully immunised - there were no more cases of asthma, wheezing or allergic reaction.
The only significant difference was found in the children who had been partially immunised, who were more likely to have reported asthma. But after taking into account other factors - such as number of brothers and sisters, exposure to tobacco smoke, and overcrowding in the home - the difference was not statistically significant.
The report concludes: "Although a number of studies using different methods have reported associations, our study provides evidence that this association was not present in a large unselected population of children.
"These findings extend the observations of our own and others' previous studies. Taken together, these observations should provide further reassurance of the lack of a positive association between pertussis immunisation and later onset of allergic diseases in children.
"Previous anti-vaccine statements led to a reduction in pertussis immunisation uptake in the United Kingdom and a subsequent rise in reported cases during the early 1980s.
"Uptake has now recovered such that 93 per cent of infants were immunised by their second birthday in 2001/ 2002. It is important to maintain these levels to prevent the known complications of whooping cough in young children."
Maitra A, Sherriff A, Griffiths M, Henderson J, ALSPAC Study Team. Pertussis vaccination in infancy is not associated with asthma or allergy in later childhood - a birth cohort study. British Medical Journal
The Department of Health says that whooping cough is particularly dangerous for young children, especially babies under 1 year old. They are most at risk from complications and death. More than a thousand cases of the disease are reported each year in England and Wales. If immunisation rates fall, whooping cough epidemics can still occur in this country. In the epidemics of the late 1970s and early 1980s, following a scare about the safety of pertussis vaccine, at least 100 children died after catching whooping cough.
Although the total number of cases fell between 1995 and 1997, there was a significant increase in whooping cough in babies under six months of age who were too young to have been fully immunised. At least 18 children died.