Introduction. Human papillomavirus (HPV) vaccination can prevent thousands of cases of anogenital cancers annually, but coverage falls short of national goals. Other vaccines recommended for adolescents (tetanus, diphtheria, and pertussis (Tdap) booster and meningococcal vaccine) have much higher coverage. Administering HPV vaccine with other vaccines concomitantly (at the same healthcare visit) could improve HPV vaccine coverage. This dissertation examined factors likely to influence concomitant uptake: seasonal variation in vaccination, vaccination school entry requirements, and patient-provider communication style. Methods. Data came from 99,921 participants in the 2008 to 2012 versions of National Immunization Survey (NIS)-Teen. Each year, NIS-Teen gathers data on adolescents (ages 13-17) through telephone interviews with parents and written questionnaires mailed to healthcare providers. In the first study, I used the Edwards method to examine cycles in individual and concomitant vaccination. In the second study, I conducted longitudinal mediation analysis with bootstrapping to test the attenuating effects of these cycles on the relationship between school entry requirements and coverage. In the third study, I analyzed the interaction between school entry requirements and communication style in their relationship with vaccination. Results. Individual vaccination was 5-10 times as common, and concomitant vaccination was 3-6 times as common, at the peaks of annual cycles compared to their troughs (all p<.001). States with school entry requirements had more extreme cycles and higher coverage for vaccines targeted by the requirements (more than 20% higher) and other adolescent vaccines (6-18% higher) than other states (all p<.001). However, contrary to my hypothesis, cycles did not mediate the relationship between school entry requirements and coverage. Regardless of states' school entry requirements, individual vaccination was higher when parents reported that providers used collaborative communication (all p<.05), but concomitant vaccination did not vary by communication style. Conclusion. Concomitant vaccination is more common in summer months, especially in states with policies requiring students to receive adolescent vaccine(s). Patient-provider communication was less influential for concomitant vaccination than for individual vaccination. To increase HPV vaccination (individual or concomitant administration), quality improvement and health promotion activities should precede summer peaks and implementation of new school entry requirements.