The Hidden Adherence Problem: HPV Vaccination Series Completion Is Not as Easy as 1, 2, 3

AUGUST 21, 2014
Newell E. McElwee, PharmD, MSPH, and Karen Woomer, MB

Pharmacists can help improve vaccination completion rates.

The recent discovery of 6 vials of smallpox in a government laboratory just outside Washington, DC,1 is a reminder of the public health impact that immunizations have had in the past century on reducing or eliminating serious infectious diseases. Smallpox was declared eradicated in 1980 and parents today no longer fear that their children will die from diphtheria or become disabled from polio.

Despite these successes, vaccination rates are still not optimal. Healthy People 2020 is a government program that establishes population health objectives every 10 years, including target vaccination rates.2 The Healthy People 2020 target for tetanus-diptheria-acellular pertussis, meningococcal conjugate, and human papillovirus (HPV) is 80%, and for varicella it is 90%. The baseline vaccination rates in 2008 were 46.7%, 43.9%, 16.6%, and 36.7%, respectively.

Vaccines that require more than 1 dose, that is, a series of repeat doses over time, are particularly challenging.2 We don’t have good evidence on whether patients who only complete a portion of the series are fully immunized, and we must therefore assume that partial series completion may not prevent the infectious disease that the vaccination targets. We will use HPV vaccination as an example to explore what factors are associated with vaccine uptake and series completion, what can be done to improve coverage rates, and what role the pharmacist can play.

Background on HPV

HPV infection is the most common sexually transmitted disease in the United States and occurs in approximately 50% of sexual active people at least once in their lifetime.3 The downstream consequences of these infections are serious. HPV types 16 and 18 cause approximately 70% of cervical cancer and the majority of other HPV-related cancers (vaginal, anal, and vulvar).4 HPV types 6 and 11 cause approximately 90% of genital warts.

Two HPV vaccines are approved for use in the United States; both are effective at preventing HPV types 16 and 18 and one is also effective at preventing types 6 and 11 (Cervarix [GSK], a bivalent vaccine and Gardasil [Merck], a quadrivalent vaccine). These vaccines are given as a series of 3 IM doses with the second dose given 1 or 2 months after the initial dose and the third dose given 6 months after the initial dose. They are generally well tolerated and close to 100% effective in preventing vaccine-type HPV infections in adolescents and young adults not previously exposed to HPV.

The potential public health impact of HPV vaccinations to significantly reduce the morbidity, mortality, and costs of HPV-related cancers is enormous. While HPV vaccination coverage in the United States has improved since the first vaccine was introduced in 2006, the number of eligible patients who complete the 3-dose vaccination series is low compared with HPV vaccination rates in other countries and to the coverage rates for other adolescent vaccines in the United States. The National Immunization Survey for Teens (NIS-Teen), conducted annually by the Centers for Disease Control and Prevention (CDC), showed in their 2013 survey that HPV vaccination series completion rates have continued to increase each year but the rates are still low.5 For example, in 2013, 57% of adolescent girls 13 to 17 years received the first dose of the vaccine, 48% received 2 doses, and only 38% completed the 3 dose series. The 2013 series completion rates for adolescent boys were even worse, with an overall series completion rate of 14%. The trajectory of these rates from 2006 to 2013 suggests that the Healthy People 2020 goal of an 80% completion rate will not be achieved unless the rate of series completion increases over the next 5 years.

Factors Associated With HPV Vaccine Uptake and Series Completion

A recent systematic review evaluating factors associated with uptake in teenage girls (9 to 18 years) identified 25 unique studies, most of them conducted in the United States (20/25 studies), and most with moderate or higher risk of bias after critical appraisal.6 Older age, history of other pediatric vaccinations, and previous health care utilization were consistently predictors of vaccine initiation and uptake. Ethnicity (Caucasian race) and having public or private health insurance were predictors of vaccine initiation and uptake in some studies, but showed no significant association in others. For series completion, ethnicity (Caucasian race) and having public or private insurance were consistent predictors of series completion.

In addition, the authors reported that uptake and series completion rates vary significantly across countries, with the United Kingdom and Portugal achieving 80% coverage rates where vaccines are free and delivered through school-based programs. This study excluded males and adult females over 17 years old. There are fewer studies addressing males and older females (18 to 26 years) and it’s not known to what extent studies of adolescent boys can be generalized to adolescent boys or adult females.

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