As allergies have been increasing, so has immunization. The hypothesis is that certain vaccines may have increased the risk of allergic disease. There are two possible mechanisms of vaccines that may have influenced the development of allergic reason. The first one is that the vaccine could have a “direct impact on the immune system, for example there is evidence that pertussis vaccine enhances humans’ response to histamine and leads to raised immunoglobulin E levels”. The second is “the mechanism in vaccines reduces the burden of childhood illness” (McKeever, Lewis, Smith, and Hubbard). Children who have older siblings are less likely to be have allergies in the future. This is due to exposure to infections during childhood, which reduces
