Among females 9–26 years of age with private insurance, we observed a decrease in the proportion of initiators who completed the quadrivalent HPV vaccine series between 2006 and 2009. Two other studies from state–level data had similar results. One of these previous studies found comparable proportions of completion among initiators, while the other also showed a declining trend in HPV vaccine completion between 2006 and 2008, similar to our observations.11, 12
Furthermore, our study found that women in the 9–12 and 13–18 year old age groups have the steepest declines in completion compared with the other two age groups. This is concerning because the average age of sexual debut in the US is 17.4 years and may be lower than 14 years in 5% of females.13
Thus, most women need to complete the series before age 18 to obtain maximum efficacy from the vaccine.
Although completion decreased over time, it is important to note that the proportion of females who received only one injection during the study period increased over the study interval. These trends may indicate that physicians are focusing more on initiating the vaccine series as time passes, but may not be following up with their patients for subsequent doses of the vaccine. It is also possible that adverse socioeconomic conditions discouraged patients from completion because the co-pay or deductible for the vaccination became burdensome for them as the recession progressed. To improve completion for the HPV vaccine series, doctors of all types should be encouraged to use various methods to remind parents and patients to return to the clinic to receive the remaining doses. Calling patients has been shown to be an effective method of reminding patients to return for immunizations of all types, although it was not found to be effective in one study of adolescents where there were problems with phone number discontinuity.14
Recently, texting has been shown to improve rates of return for a subsequent HPV vaccine dose.15
This may offer a less expensive alternative to phone calls to remind patients to return for vaccinations.
In this sample, there were differences in the odds of administering the first vaccine to completers by physician specialties. “Clinics, hospitals, and other facilities,” nurses, specialists, and family practitioners, were less likely to administer a first vaccination to completers than pediatricians. However, it was observed that obstetricians/gynecologists were more likely to administer the first dose of the vaccine to completers than pediatricians. Similar to the results in our study, vaccine initiators in North Carolina who received their injections from family providers or hospitals were less likely to complete than those who received them from pediatricians.12
This indicates that physicians who initiate the HPV vaccination, but may not be as familiar with the recommendations of the series or may not be the primary care provider of the patient, need to stress the importance of completing the series and follow up with their patients. This is particularly important in clinics, hospitals, and other facilities where patients may not seek continuous care. If the patient returns to these providers, the opportunity should be taken to administer remaining vaccinations, as it has been shown that when patients do return to the same clinic facilities, they often do not receive additional vaccinations, even if their visit coincides with the time the vaccinations are due.16
Providing the facilities with the means to flag the records of patients who have received the first vaccine may improve completion rates for patients who do return. The increasing use of electronic medical records may make it easier for facilities to do this.
This study also included data on those women greater than 26 years of age who received HPV vaccinations on an off-label basis. Older women who initiate this vaccine series may view themselves as having a higher risk for contracting HPV which may account for the demand we observed among this age group. Although the vaccine is currently not recommended for women over age 26, research indicates that it is safe and effective in the development of immunogenicity to HPV infections in women up to 45 years old.17
Future research should investigate the benefits of extending current vaccine recommendations to include older women so that physicians can adequately counsel those who express interest.
The insurance records we examined also indicated that some males initiated the HPV vaccine before it was licensed or recommended for use in this population. They were excluded from this study because the FDA did not license the quadrivalent vaccine for routine use in males until October of 2009. Its use in males was not recommended by the ACIP until October of 2011, at which time they changed their recommendations to include initial vaccinations for boys 11–12 years of age with catch-up vaccination for those 13–21 years old who had not already been vaccinated. They also stated that males as young as 9 years and up to 26 years of age could receive the vaccine. The males in this data base who received the vaccine must have been very motivated, considering the difficulties they likely would have encountered in finding a physician who would administer the vaccine outside of FDA licensure. Economic research has indicated that if an adequate proportion of women are not vaccinated, then vaccinating males is a cost-effective method of preventing genital warts and precancerous conditions related to HPV 6/11/16/18 among women.18, 19
The low prevalence of females who have initiated and completed the HPV vaccine series in the US20
thus far indicates that vaccination of males would not only decrease their risk of genital warts and several cancers, but also help reduce the burden of cervical cancer in the US.
This study was not able to capture enrollees who dropped out of the insurance plan they had when they received the first vaccine dose but completed the series later, which may have led to a loss of enrollees who completed the series of vaccinations. However, it is likely that the proportion that completed is higher among enrollees who were continuously enrolled in their insurance plan, as it indicates more stability in their financial situation. Thus, our results are likely conservative estimates of HPV vaccination completion among insured females. In addition, sociodemographic characteristics were not available, which may have introduced some bias into the study which cannot be addressed.
This study only assessed the proportion of females that completed the quadrivalent HPV vaccine, and did not assess the proportion that completed the bivalent HPV vaccine. However, the bivalent vaccine is not commonly used in the US, and there were very few cases that initiated or included a code for the bivalent HPV vaccine in the claims dataset. Therefore, it is unlikely that including these cases would have changed the analyses. Furthermore, completion was defined as three vaccinations in 365 days, which means that 286 subjects did receive at least 3 doses, but not in one year’s time. Although these patients may gain adequate immunity from three vaccinations outside of one year’s time, the format that was chosen for this study follows more closely the guidelines of the ACIP.
Among insured females in this study, younger females had a noted decrease in the odds of completing each year compared to older females. This decrease could reduce the effectiveness of the vaccine in preventing HPV that is associated with anogenital malignancies. However, more females received one vaccine indicating a shift in emphasis from completion to simple initiation among providers of insured females. Thus, it is important that all providers who initiate the HPV vaccine series make an effort to follow up and stress the importance of completing the vaccine series to their patients. Calling or texting patients or the patients’ parents may be important methods of increasing HPV vaccine series completion among this population.