The Hygiene Hypothesis -- Unrelated to Vaccination


My name is Paul Offit. I am talking to you today from the Vaccine Education Center here at the Children's Hospital of Philadelphia. In mid-December an interesting study was presented by researchers at the University of Leipzig in Germany, looking at the relationship between allergies—specifically eczema—and the receipt of vaccines. Did receiving vaccines increase the rate of eczema? They found that it didn't, and this isn't a surprising finding. In fact, it duplicates other findings for other allergy symptoms, such as asthma.

Where does this all come from? Why would someone even bother doing this study? The answer is the "hygiene hypothesis." There is this notion that children in the developing world are less likely to develop such allergies as eczema and asthma compared with children in the developed world. That is a fact. The thinking behind why this happens is that children in the developing world are more likely to be exposed to pathogens like parasites, pathogen-producing bacteria, and viruses early in life. This educates them away from the Th2 (allergic) bias they are born with, toward a Th1 cell (nonallergic) bias. By giving them vaccines early in life, the idea is that we reduce the number of challenges the child receives, so that we don't educate them away from that Th2 bias at birth and towards the Th1.

There are a lot of reasons why the hygiene hypothesis should have nothing to do with vaccination. The first reason is that the diseases that vaccines prevent occur independent of the level of hygiene in the home and the sanitation in the country. Varicella occurred in everybody independent of what country they lived in. The same thing was true of measles, mumps, rubella, etc.

The second is that it just doesn't make sense that you would significantly reduce the number of pathogens you are exposed to by vaccination, because we are still exposed to many pathogens. We are exposed to rhinoviruses, adenoviruses, parainfluenza viruses, caliciviruses, astroviruses, and Norwalk viruses. We still have plenty of chances to educate ourselves away from a Th2 bias. These findings, from the study that was performed at the University of Leipzig in Germany, were exactly what we would expect. We can be reassured that vaccines don't increase the risk for allergic disease.

Thank you for your attention.