Postexposure antibiotics should also be given to the following high-risk people within 21 days of exposure, whether they have been vaccinated or not: Infants < 12 months Women in the 3rd trimester of pregnancy All people with health conditions potentially exacerbated by pertussis infection (eg, immunodeficiency, moderate to severe asthma, chronic lung disease) People who have close contact with infants < 12 months, pregnant women, or patients with conditions that may result in severe illness or complications All people in high-risk settings that include infants < 12 months or women in the 3rd trimester of pregnancy (eg, child care centers, maternity wards, neonatal intensive care units) These people should be given a 7 - to 14-day course of oral erythromycin 500 mg 4 times a day or 10 to 12.5 mg / kg 4 times a day.