Passage: The Haemophilus influenzae type B vaccine, often called Hib vaccine, is a vaccine used to prevent Haemophilus influenzae type b (Hib) infection. In countries that include it as a routine vaccine, rates of severe Hib infections have decreased more than 90%. It has therefore resulted in a decrease in the rate of meningitis, pneumonia, and epiglottitis.It is recommended by both the World Health Organization and Centers for Disease Control and Prevention. Two or three doses should be given before six months of age. In the United States a fourth dose is recommended between 12 and 15 months of age. The first dose is recommended around six weeks of age with at least four weeks between doses. If only two doses are used, another dose later in life is recommended. It is given by injection into a muscle.Severe side effects are uncommon. About 20 to 25% of people develop pain at the site of injection while about 2% develop a fever. There is no clear association with severe allergic reactions. The Hib vaccine is available by itself, in combination with the diphtheria/tetanus/pertussis vaccine, and in combination with the hepatitis B vaccine, among others. All Hib vaccines that are currently used are conjugate vaccine.An initial Hib vaccine was developed in 1977 which was replaced by a more effective formulation in the 1990s. As of 2013, 184 countries include it in their routine vaccinations. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. The wholesale cost of a pentavalent vaccine which includes Hib in the developing world was US$15.40 per dose as of 2014. In the United States it costs about $25–50 per dose.

Question: When should the first dose be given?
six weeks of age