Discussion

In the USA, HPV vaccination rates remain much lower than recommended by public health officials, leading to thousands of preventable instances of cervical cancer each year [Reference Lin8, Reference Walker9]. Disparities in the incidence of cervical cancer between Blacks, Hispanics and Whites living in the USA are thoroughly discussed in the literature. In contrast – likely in part due to the ‘model minority’ stereotype – relatively few studies have explored HPV vaccine uptake and cervical cancer diagnosis among Asian Americans, with even fewer studying people of south-Asian decent (i.e. POIA) [Reference Ghosh10–Reference Yi12]. Through our analysis of NHIS data, we found that POIA between the ages of 18 and 64 exhibit significantly lower HPV vaccine initiation rates than members of other racial groups living in the USA. This discovery aligns with other findings regarding HPV vaccination among Asian Americans in general. For instance, one study examined the 2013–2016 National Health and Nutrition Examination Surveys (NHANES) and found that Asians between the ages of 9 and 26 have the lowest HPV vaccination rate of all racial/ethnic groups in the USA [Reference Patel13] 39.6% vs. 48.4%, 49.2%, 42.4% and 42.6% for White, Black, Mexican American and ‘Other Hispanic’ Americans, respectively [Reference Patel13]. Commonly reported barriers to HPV vaccination among Asian Americans include: lack of provider recommendation [Reference Dela Cruz14–Reference Lee16], belief that only promiscuous women are at risk of HPV infection and cervical cancer [Reference Lee and Lee17], lack of HPV vaccine education by healthcare providers [Reference Khan18] and cultural factors causing sexual health stigma and hesitancy towards utilising women's health services [Reference Lee and Lee17].

While the NHIS did not specifically field questions as to why POIA had a lower vaccination rate than others in the US population, our analysis evaluating differences between those who got an HPV vaccine vs. those who did not shed some light on factors that predict vaccine uptake in this population. For example, we found that POIA who were born in the USA had a significantly higher rate of initiating HPV vaccination than those who immigrated. This seemed to be independent of English language proficiency or level of education and speaks potentially to the effect of acculturation and/or access on vaccine uptake. Other studies have similarly found that individuals born in the USA initiated the HPV vaccine series at twice the rate of those born outside the USA [Reference Adjei Boakye19]. Indeed, some have suggested that POIA born in the USA may have greater access to HPV education and vaccination than those born outside the USA and may face less stigma in discussing or seeking treatment for sexual health-related matters [Reference Khan18, Reference Ismail20]. While it would have been nice to look at age of immigration (and whether this was before or after the recommended age for the HPV vaccine), the NHIS is limited in that it does not contain this information. This, however, would be interesting to evaluate in further studies.

In our analysis, all patients who obtained an HPV vaccine stated they spoke English very well. This correlation of HPV vaccination with high levels of English proficiency is consistent with other studies which have found that Asian Americans commonly cite language barriers as a reason underlying their lack of HPV vaccination [Reference Lee and Lee17], and those with higher English fluency are more receptive to receiving HPV vaccination for themselves and their families [Reference Nguyen, Chen and Chan21, Reference Yi22]. Again, age at immigration may be correlated with English language proficiency. Unfortunately, the NHIS does not provide data on age at immigration or duration of residence. This would be interesting to evaluate in further studies.

In addition, while one may have anticipated a correlation between HPV vaccine uptake and educational status, we did not find this. Taylor et al. similarly found no correlation between educational status and HPV vaccination uptake in their study of Cambodian Americans [Reference Taylor15]. This may be related to the fact that there may be a decoupling of socio-cultural beliefs and academic education in terms of whether Asians, and particularly POIA, opt to take the HPV vaccine.

Also surprisingly, we found no relationship between family income relative to the federal poverty level and POIA HPV vaccine uptake; however, data regarding the relationship between socio-economic status and vaccine uptake in the USA have been mixed [Reference Larson23]. For instance, one study found low income to be a barrier to vaccination [Reference Wu24], while another study found high-income as a barrier to vaccination [Reference Wei25]. Thus it seems that perceived cost, rather than simply income level, is a key barrier to obtaining the HPV vaccine among Asian Americans [Reference Kim26–Reference Vu28].

Indeed we, like many studies evaluating a plethora of health maintenance and disease prevention strategies, found that insurance coverage to be a critical factor for uptake of HPV vaccine among POIA. Hopfer et al. in their narrative analysis, found restrictive insurance policies to be a significant barrier to HPV vaccine uptake among Asian Americans [Reference Hopfer29], such that some Asian Americans forgo receiving HPV vaccination due to uncertainty regarding whether their insurance policy covers the vaccine [Reference Dela Cruz14]. Our finding on the impact of insurance status on HPV vaccine uptake among POIA was independent of family income, education, place of birth or English proficiency, suggesting that provision of HPV vaccines as part of a federally provided mandate (regardless of insurance status) may improve vaccination rates.

Our finding that younger women were more likely to have received the HPV vaccine was not unexpected. Other studies have similarly found that younger Asian American individuals are more likely to initiate HPV vaccination [Reference Tung30]. When the HPV vaccine initially became available in the USA in 2006, it was initially recommended only for cervical cancer prevention, with girls between the ages of 9 and 26 being targeted for vaccination. More recently in 2019, guidance has expanded to include a strategy of ‘shared decision making’ for HPV vaccination for all adults (regardless of gender) through age 45. This, however, occurred after the 2018 NHIS survey, upon which the current study is based. Interestingly, some studies found that parental belief that their children were too young to obtain HPV vaccination decreased uptake in Asian American children [Reference Dela Cruz14]. Given that, as of 2018, HPV vaccination was received in a doctor's office setting by 79.2% of recipients aged 13–17 in the USA, parental beliefs could strongly influence HPV vaccine uptake among POIA youth [Reference Lu7].

While we, like others, found that single individuals are more likely to obtain HPV vaccination than married people [Reference Thompson31, Reference Hollins32], this may be related to the fact that single people are more likely to be younger, and therefore this variable may be collinear with age. Indeed, on our multivariable analysis, neither age nor marital status were independent predictors of HPV vaccination. Some, however, have argued that married individuals perceive their risk of HPV infection as low due to having a single sexual partner, whereas those who are single may perceive themselves as being at higher risk of HPV infection due to having multiple sexual partners [Reference Thompson33].

Regarding HPV vaccine series completion rates, we found that POIA between the ages of 18 and 64 who initiate HPV vaccination are equally likely to complete the three-dose series compared to other major racial groups in the USA. These data echo findings from the 2018 National Immunization Teen Survey. This work found that Asian American teenagers (aged 13–17) completed the HPV vaccine series at roughly the same rate as White, Black and Hispanic teenagers (53.1% vs. 47.8%, 53.3% and 56.3%, respectively) [Reference Hirth34]. Interestingly, Agénor et al., evaluating data from the 2015 NHIS, found that Asian women had significantly lower odds of completing the HPV vaccination series when compared to White women [Reference Agénor35]. While they did not subclassify Asian women as we did, the 2018 NHIS data do not seem to suggest a significant difference in HPV completion rates among women who initiated HPV vaccination by the racial group (P = 0.7658), although a difference is seen in initiation rates (P = 0.0091), echoing our findings among POIA. These data suggest that racial disparities in HPV vaccination rates that may have existed in the past may have dissipated in recent years.

Our data should be viewed in light of its inherent limitations. As a survey study, it is limited by the questions fielded and is subject to recall bias. Furthermore, we recognise that in 2016, guidelines changed to allow for two doses of HPV instead of three, and our study defined completion of the series using the older definition which would have applied to the majority of people in our cohort. We recognise, however, there was some variability in the guidelines and there was no way for our study to control for this.

Despite these limitations, our study has a number of strengths. Given the design of the NHIS which is representative of the entire US population, this dataset gives us key insights into factors affecting HPV vaccination rates among POIA. Importantly, while our data demonstrate that POIA are less likely to receive an HPV vaccine than other racial groups, they are just as likely to complete their vaccination schedule once started. As such, targeted public health measures increasing awareness and acceptance of HPV vaccination among POIA may be particularly effective in increasing immunity to HPV among this community. Furthermore, our finding that those born in the USA were more likely to get vaccinated provides hope that, with acculturation and growing acceptance of the vaccine among those born here, HPV vaccination will be higher among POIA in the USA than it is in their ancestral homeland. Among those POIA who continue to migrate to the USA, recognition of disparities in HPV vaccine uptake by clinicians is crucial to increasing HPV vaccination rates within this population. Given recent policy changes allowing for HPV vaccine administration in both men and women up to 45 years old, clinicians should enquire about and discuss HPV vaccination with their migrant POIA patients to promote shared decision making and increased HPV vaccine uptake in this population. Finally, our data highlight insurance as being a key factor that can enhance HPV vaccination rates, suggesting that making HPV vaccines available regardless of insurance status may be a key public health measure to improve vaccination rates and ultimately reduce preventable malignancies associated with HPV – not just for POIA, but for the population as a whole.