aged 14 (the hexavalent vaccine is given to infants and provides the first stage of protection against diphtheria, tetanus, and polio, as well as pertussis, Haemophilus influenzae type B and hepatitis B). Subsequent boosters are recommended for foreign travellers where more than 10 years has passed since their last booster. This is provided on the NHS free of charge due to the significant risk that an imported case of polio could pose to public health in Britain. United States The standard immunization regimen for children within the United States is five doses of DTaP between the ages of two months and fifteen years. To be considered fully vaccinated, the Center for Disease Control and Prevention (CDC) typically requires five doses of Tdap. The CDC recommends that children receive their first dose at two months, the second dose at four months, the third dose at six months, the fourth dose between 15 and 18 months, and the fifth dose between 4–6 years. If the fourth dose of the DTaP immunization regimen falls on or subsequent to the recipient's fourth birthday, the CDC states that only four doses are required to be fully vaccinated. In the instance that an individual under 18 has not received the DTaP vaccine, individuals should be vaccinated on the schedule in accordance with the vaccination "catch up schedule" provided by the CDC. Infants younger than 12 months of age, specifically less than three months of age, are at highest risk of acquiring pertussis. In U.S, there is no current tetanus-diphtheria-pertussis vaccination (whooping cough) recommended or licensed for new born infants. As a result, in their first few months of life, unprotected infants are at highest risk of life-threatening complications and infections from pertussis. Infants should not receive pertussis vaccination younger than six weeks of age. Ideally, Infants should receive DTaP (name of whooping cough vaccine for children from age 2 months through 6 years) at 2, 4, 6 months of age and they are not protected until the full series is completed. To protect infants younger than twelve months of age not vaccinated with Tdap against pertussis, ACIP also recommends adults (e.g., parents, siblings, grandparents, childcare providers, and healthcare personnel) and children to receive Tdap at least two weeks before being in contact with the infant. The CDC recommends that adults who have received their childhood DTP series receive a Td or Tdap booster every ten years.