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Monday, September 12, 2011

Delay in diphtheria, pertussis, tetanus, vaccination is associated with a reduced risk of childhood asthma.

Asthma is the most common childhood disease in industrialized countries.  The increase in asthma has occurred along side improvements in hygienic standards and vaccinations.  Vaccines are important as they have prevented much illness and death.  However, researchers wonder if they play a role in the development of asthma.
Studies looking at an association between asthma and vaccinations show mixed results.  Some show that vaccines increase the risk, other show that vaccines decrease the risk and some show no association.  In other studies, researchers found that children have LESS of a risk of developing asthma if vaccines are given later.
Our research question: Does the timing of diphtheria, pertussis (whooping cough), and tetanus vaccinations (DPT) affect the development of asthma in childhood?
Research findings:
The SAGE study examined immunization and health care records of 14,000 children born in Manitoba in 1995 who still live in the   province. This study showed that children who had their first routine vaccination delayed by more than 2 months cut their risk of getting asthma in half.  Nearly 14% of children who received their first shot of diphtheria, pertussis, and tetanus vaccine at 2 months of age developed asthma, compared to 5.9% of children who were vaccinated later. The study also showed that more boys than girls developed asthma (3 boys to 2 girls) and children who developed asthma lived mostly in cities (70%). It is important to note that these children received a different type of DPT vaccine than what is used now. Children have been receiving a new version of the vaccine since late 1997.
What do these results mean?
This study tells us what is happening, but it does NOT tell us WHY it is happening. One of the main reasons children are immunized later than recommended is because the child has a fever or an infection at the time they should receive it. We know that fever or infection during the first year of life can help prevent the development of asthma. It may be that children are protected from asthma due to the fever or the infection and not because the vaccination was given later.
Delaying the first vaccine (DPT) by 2 months or more is associated with lower rates of asthma in childhood.  The exact cause of the decreased rate of asthma is not clear. It is important to note that children who participated in this study received a different type of DPT vaccine than what given today.  We don't know if the same results would be seen using today’s vaccine.
The results of this study should not be used to spur a change in the province’s vaccination schedule. More research needs to be done on the new vaccine to see if the results are the same. Further research is also needed to see if early life infections are the reason for delayed immunization and protection against the development of asthma. 
The co-author of this study, Dr. Allan Becker, says: “It is important to continue to have your children immunized on the current schedule. The benefits of childhood vaccination far outweigh the risks.  The safety and effectiveness of vaccines have been studied for years. You can not use this study to predict what would happen to today’s children getting immunizations because the vaccination used now is different. There are far fewer side effects now, and even in 1995 when there was a risk of high fever, that risk was far outweighed by the benefits. In countries where immunizations went down or were delayed, childhood illnesses went up. These are serious illnesses that cause major problems and some capable of causing death in children”.
Delay in diphtheria, pertussis, tetanus vaccination is associated with a reduced risk of childhood asthma. McDonald KL, Huq SI, Lix LM, Becker AB, Kozyrskyj AL., J Allergy Clin Immunol. 2008 Mar;121(3):626-31. Epub 2008 Jan 18.

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