I just found this on BabyCenter, an article exploring the possibility of a connection.
Then I found this article, discounting a connection between the pertussis vaccine and asthma. (Which also led me to this great resource.)
And then I found this article, which says a connection between childhood vaccines and atopic conditions (including asthma) is unlikely -- but doesn't discount it entirely.
Here's one from the Vaccine Education Center at Children's Hospital of Philadelphia. Guess what it says?
By far the most compelling one is here. You need a medical dictionary and possibly an interpreter to get through the whole thing, but here's the executive summary:
Background: A few previous studies have suggested that childhood vaccines, particularly whole cell pertussis vaccine, may increase the risk of asthma. We evaluated the suggested association between childhood vaccinations and risk of asthma.
Methods: Cohort study involving 167 240 children who were enrolled in 4
large health maintenance organizations during 1991 to 1997, with follow-up from
birth until at least 18 months to a maximum of 6 years of age. Vaccinations were
ascertained through computerized immunization tracking systems, and onset of
asthma was identified through computerized data on medical care encounters and
Results: In the study 18 407 children (11.0%) developed asthma, with a
median age at onset of 11 months. The relative risks (95% confidence intervals) of asthma were: 0.92 (0.83 to 1.02) for diphtheria, tetanus and whole cell pertussis vaccine; 1.09 (0.9 to 1.23) for oral polio vaccine; 0.97 (0.91 to 1.04) for measles, mumps and rubella (MMR) vaccine; 1.18 (1.02 to 1.36) for Haemophilus influenzae type b (Hib); and 1.20 (1.13 to 1.27) for hepatitis B vaccine. The Hib result was not consistent across health maintenance organizations. In a subanalysis restricted to children who had at least 2 medical care encounters during their first year, the relative risks decreased to 1.07 (0.71 to 1.60) for Hib and 1.09 (0.88 to 1.34) for hepatitis B vaccine.
Conclusion: There is no association between diphtheria, tetanus and whole cell pertussis vaccine, oral polio vaccine or measles, mumps and rubella vaccine and the risk of asthma. The weak associations for Hib and hepatitis B vaccines seem to be at least partially accounted for by health care utilization or information bias.