History
Polysaccharide vaccine
The first Hib vaccine licensed was a pure polysaccharide vaccine, first marketed in the United States in 1985. Similar to other polysaccharide vaccines, immune response to the vaccine was highly age-dependent. Children under 18 months of age did not produce a positive response for this vaccine. As a result, the age group with the highest incidence of Hib disease was unprotected, limiting the usefulness of the vaccine. The vaccine was withdrawn from the market in 1988. Conjugate vaccine
The shortcomings of the polysaccharide vaccine led to the production of the Hib polysaccharide-protein conjugate vaccine. The first such vaccine available in the United States was based on work done by American scientists John Robbins and Rachel Schneerson and was available in 1987. Attaching Hib polysaccharide to a protein carrier greatly increased the ability of the immune system of young children to recognize the polysaccharide and develop immunity. There are currently three types of conjugate vaccine, utilizing different carrier proteins for the conjugation process: inactivated tetanospasmin (also called tetanus toxoid); mutant diphtheria protein; and meningococcal group B outer membrane protein. Combination vaccines
Multiple combinations of Hib and other vaccines have been licensed in the United States, reducing the number of injections necessary to vaccinate a child. Hib vaccine combined with diphtheria-tetanus-pertussis–polio vaccines and hepatitis B vaccines are available in the United States. The World Health Organization (WHO) has certified several Hib vaccine combinations, including a pentavalent diphtheria-pertussis-tetanus-hepatitis B-Hib, for use in developing countries.
Psychological impact
ED often has an impact on the emotional well-being of both men and their partners. Many men do not seek treatment due to feelings of embarrassment. About 75% of diagnosed cases of ED go untreated. Causes
Causes of or contributors to ED include the following:

Diets high in saturated fat are linked to heart diseases, and men with heart diseases are more likely to experience ED. By contrast, plant-based diets show a lower risk for ED. Prescription drugs (e.g., SSRIs, beta blockers, antihistamines, alpha-2 adrenergic receptor agonists, thiazides, hormone modulators, and 5α-reductase inhibitors)
Neurogenic disorders (e.g., diabetic neuropathy, temporal lobe epilepsy, multiple sclerosis, Parkinsons disease, multiple system atrophy)
Cavernosal disorders (e.g., Peyronies disease)
Hyperprolactinemia (e.g., due to a prolactinoma)
Psychological causes: performance anxiety, stress, and mental disorders
Surgery (e.g., radical prostatectomy)
Ageing: after age 40 years, ageing itself is a risk factor for ED, although numerous other pathologies that may occur  with ageing, such as testosterone deficiency, cardiovascular diseases, or diabetes, among others, appear to have interacting effects
Kidney disease: ED and chronic kidney disease have pathological mechanisms in common, including vascular and hormonal dysfunction, and may share other comorbidities, such as hypertension and diabetes mellitus that can contribute to ED
Lifestyle habits, particularly smoking, which is a key risk factor for ED as it promotes arterial narrowing. Due to its propensity for causing detumescence and erectile dysfunction, some studies have described tobacco as an anaphrodisiacal substance.