Chloroquine might diminish the immune response to CVD 103-HgR. The vaccine manufacturer, Emergent BioSolutions, recommends that CVD 103-HgR be administered 10 days or more before starting chloroquine. Doxycycline, a tetracycline antibiotic, is often used for malaria prophylaxis. The manufacturer does not recommend administration of the vaccine with oral antibiotics and does not recommend administering CVD 103-HgR to a person within 14 days prior to vaccination. The optimal duration between completion of CVD 103-HgR and then starting doxycycline is unknown.