Several studies have shown a connection between vaccinations and a higher risk of developing asthma, particularly vaccines administered in the first few months of life. In a study in Manitoba published in 2008, researchers found that children who delayed the DPT vaccine by 2 months developed asthma by age 7 at a rate of 6 per 100, versus 14 per 100 for children who vaccinated with DPT per the schedule DPT is the vaccine diphtheria-pertussis-tetanus (pertussis is also known as “whooping cough”). In other words, about 8 of every 100 children could have vaccine-induced asthma. See Earlier Vaccination Causes Asthma for a more detailed description. Applied to the USA, this indicates that the DTaP vaccine in the USA carries a greater than 1 in 13 risk of vaccine-induced asthma:
The CDC’s Asthma-Vaccine study found that the Hib and Hepatitis B vaccines (both given in the first 6 months of life) increase the risk of developing asthma by 18 and 20 percent respectively. See CDC Asthma-Vaccine Study. To apply the Manitoba study’s numbers to vaccine-induced asthma risk in the USA, some factors need to be considered. The Manitoba study addressed children born in 1995 who received the DPT vaccine, which has since been replaced by the DTaP (diphtheria-tetanus-acellular pertussis) vaccine because of the higher risk of brain encephalopathy from the DPT vaccine. Although the DTaP vaccine may be safer than the DPT vaccine regarding brain encephalopathy, the asthma rates in Canada and the USA have not materially changed since the transition from DPT to DTaP which indicates that the asthma risk is similar for both vaccines. The vaccine-induced asthma risk, when extrapolated to the USA, resulted in the same risk as in Canada since the USA asthma prevalence of 13.8% in 2009 matches the 13.8% Canadian asthma prevalence. Although not explicitly stated, the children in this study likely received the Hib vaccine at the same time as the DPT vaccine (the Hepatitis B vaccine was not and still is not on the Canadian schedule, but is on the USA schedule). Since the CDC study shows that Hepatitis B increases asthma risk by 20%, it is possible that the percentage of USA asthma cases that are vaccine-induced is higher than in Canada. But to be conservative, the % of vaccine-induced asthma cases is considered the same in this analysis.