Early childhood immunizations have been viewed as promoters of asthma by:
- stimulating a TH2-type immune response
- decreasing "microbial pressure," thus shifting the balance between TH1 and TH2 immunity
Th1 and Th2 subsets (mind map).
Canadian researchers found that among 11, 531 children who received at least 4 doses of diphtheria, pertussis, tetanus (DPT), the risk of asthma was reduced to ½ in children whose first dose of DPT was delayed by more than 2 months.
Mayo Clinic on Apr 8, 2011: Whooping cough. It's a bacterial infection that's risen to epidemic levels in some parts of the U.S. In adults, the symptoms can be mild, but if the infection is spread to a baby who hasn't yet received a full course of vaccinations, whooping cough can be very serious.
Delay in diphtheria, pertussis, tetanus vaccination is associated with a reduced risk of childhood asthma. JACI, Volume 121, Issue 3, Pages 626-631 (March 2008).