The likelihood of developing allergies is inherited and related to an irregularity in the immune system, but the specific allergen is not.The risk of allergic sensitization and the development of allergies varies with age, with young children most at risk. Several studies have shown that IgE levels are highest in childhood and fall rapidly between the ages of 10 and 30 years. The peak prevalence of hay fever is highest in children and young adults and the incidence of asthma is highest in children under 10.Ethnicity may play a role in some allergies; however, racial factors have been difficult to separate from environmental influences and changes due to migration. It has been suggested that different genetic loci are responsible for asthma, to be specific, in people of European, Hispanic, Asian, and African origins. Hygiene hypothesis
Allergic diseases are caused by inappropriate immunological responses to harmless antigens driven by a TH2-mediated immune response. Many bacteria and viruses elicit a TH1-mediated immune response, which down-regulates TH2 responses. The first proposed mechanism of action of the hygiene hypothesis was that insufficient stimulation of the TH1 arm of the immune system leads to an overactive TH2 arm, which in turn leads to allergic disease. In other words, individuals living in too sterile an environment are not exposed to enough pathogens to keep the immune system busy.
Schedule of vaccination
As with all immunizations, whether it is available or required, and under what circumstances, varies according to the decisions made by local public health agencies. Children under the age of two years fail to mount an adequate response to the 23-valent adult vaccine, and so a pneumococcal conjugate vaccine is used. While this covers only seven strains out of more than ninety strains, these seven strains cause 80% to 90% of cases of severe pneumococcal disease, and it is considered to be nearly 100% effective against these strains. United Kingdom
The UK childhood vaccination schedule for infants born after 31 December 2019, consists of a primary course of one dose at twelve weeks of age with a second dose at one year of age. For infants born before 1 January 2020 and those in Scotland, the childhood vaccination schedule consists of a primary course of two doses at eight and sixteen weeks of age with a final third dose at one year of age.Children at special risk (e.g., sickle cell disease and asplenia) require as full protection as can be achieved using the conjugated vaccine, with the more extensive polysaccharide vaccine given after the second year of life:

United States
In 2001, the Centers for Disease Control and Prevention (CDC), upon advice from its Advisory Committee on Immunization Practices (ACIP), recommended the vaccine be administered to every infant and young child in the United States. The resulting demand outstripped production, creating shortages not resolved until 2004.