Parental Country of Birth and Childhood Vaccination Uptake in Washington State

Discussion

We found that children of Somali-born parents were less likely to be vaccinated with measles-containing vaccines compared with children of US-born parents. Children of Somali-born parents did not show decreases relative to children of US-born parents in the other vaccines. The decreased measles vaccination coverage of children with Somali-born parents that we observed is consistent with the findings of the aforementioned Minnesota study.⁴ It is also consistent with MMR vaccine hesitancy identified by qualitative research in the Seattle Somali community.¹³ Qualitative research in both Washington State and Minnesota has revealed that MMR vaccine hesitancy among Somalis is primarily linked to the belief that MMR causes autism.^5,13 The fact that refusal of measles-containing vaccines by Somali parents in our study was specific and did not extend to the other included vaccines lends further credence to this explanation.

Similar to the Minnesota study, the decrease in measles vaccination coverage among Somali children became more pronounced over time. It should be noted, however, that the decline in the Minnesota study began in 2008, whereas the decline in our study began in 2011 (corresponding to the 2010 birth year). The Minnesota Somali community receives frequent visits by Dr Wakefield,^6,25,26 the author of the retracted article that first purported an erroneous link between MMR and autism.²⁷ Somali families in Washington are in frequent contact with friends and family in Minnesota (F. Mohamed, personal communication, 2015). It is possible that the trend we observed represents the adoption of Minnesota-based vaccine hesitant beliefs.

In contrast to the specific effect on measles vaccination seen in children of Somali-born parents, children of Ukrainian and Russian-born parents had lower vaccination coverage with all included vaccines. One explanation is that vaccine refusal among these immigrant communities is associated with a more general fear of vaccines. Focus groups set up by the Washington State Department of Health involving Russian-speaking immigrants (including Ukrainians) revealed that the beliefs underlying their vaccine hesitancy were multifactorial and included fear of adverse events following immunization, fear of multiple vaccines given simultaneously, suspicion of corrupt medical authorities in their home countries as well as in the United States, and dissatisfaction with their doctor–patient relationship stemming from language and cultural barriers.²² Given the widespread effect on all of the vaccines, the hesitancy among Ukrainian and Russian immigrants does not seem to be solely rooted in the MMR autism controversy.

Vaccine refusal by Ukrainian and Russian-born parents in the United States may also be linked to vaccine refusal in their home countries. In 2009, the Ukrainian media reported an erroneous link between the death of a 17-year-old boy and the measles-containing vaccine.²⁸ The cause of his death was subsequently found to be septic shock, unrelated to the vaccine, but misleading media reports fueled widespread vaccine refusal. Several million doses of vaccines subsequently went unused and had to be incinerated. It is unclear why coverage with the hepatitis A vaccine was so low among the Ukrainian and Russian groups in our study. The hepatitis A vaccine is 1 of the newest vaccines introduced in the toddler age group and may therefore be subject to greater suspicion. In addition, it is the only vaccine in this study that is not included in state child care and school entry requirements. Another explanation may be that these families perceived the risk associated with hepatitis A disease to be low. More research needs to be done to understand why there may be particular refusal of this vaccine among Ukrainian and Russian immigrants.

We found that children of parents born in Mexico or India were more likely to be immunized with each of the included vaccines compared with children of US-born parents. The latest National Immunization Survey revealed that there were no differences in vaccination coverage between Hispanic Americans and white non-Hispanic Americans with almost all childhood vaccines.²⁹ That survey includes all those who identify as Hispanic, not just children of Mexican-born parents. One explanation for the findings in our study may be the lack of acculturation among first-generation immigrant parents. A study in California revealed that childhood vaccination coverage was lower in more acculturated Latino families compared with less acculturated Latino families.³⁰ Relatedly, another study revealed that Hispanic girls living in predominantly Hispanic neighborhoods were more likely to be vaccinated against human papillomavirus compared with Hispanic girls living in predominantly white neighborhoods.³¹ It is unclear why acculturation seems to heighten vaccine refusal. As English fluency increases, families may be more exposed to antivaccine rhetoric through English-speaking media. It is also conceivable that the longer Mexican-American families live in the United States, the more likely they are to come into contact with vaccine-refusing parents.

One might hypothesize that parents from Mexico and India are more likely to vaccinate their children against VPDs compared with US-born parents because they have more direct experience with VPDs compared with native US-born parents. Although this may indeed be true, the same cannot be said for parents from Somalia, Ukraine, or Russia where outbreaks of VPDs, including measles, also regularly occur.^32–34

One potential limitation in our study is the lack of completeness of the WAIIS. However, the WAIIS is populated by Washington State birth certificates and is considered to be almost complete by most measures. In 2011, there were 102.5% active cases in WAIIS compared with live births in Washington State (J. Warren, personal communication, 2013).³⁵ Only 2% of providers statewide do not participate in WAIIS.³⁶ One study revealed that only 1.0% of vaccinations recorded in a large local integrated health care organization could not be found in the WAIIS database.²¹ Another limitation is the possibility of secondary migration (movement from state to state after arrival in the United States). Within WAIIS it is impossible to distinguish between an undervaccinated child and 1 who has moved out of state. Secondary migration is known to occur among certain refugee and nonrefugee immigrant groups.³⁷ However, secondary migration is unlikely to explain the phenomenon of lower measles vaccination coverage in the Somali group, because we found no decrease in other vaccinations during the same study period. Secondary migration may have played a role in the Ukrainian and Russian groups, although Washington State tends to be the recipient of secondary migration by Russian-speaking refugees.³⁷

There is also the question about whether our findings signify vaccine refusal or some other phenomenon such as poor health care access or decreased health care utilization. Washington State is a “universal purchase state” meaning that the state buys childhood vaccines in bulk and supplies them to providers at no cost.³⁸ Nevertheless, it is possible that children from certain immigrant groups are less likely to attend well child-care visits for other reasons. Differences in health care access and utilization are unlikely to explain the findings in the Somalia group because nonmeasles-containing vaccines were unaffected. It could explain the findings in the Ukraine and Russia groups, although when we adjusted for number of prenatal visits (as an albeit imperfect marker of access and health care utilization) there was no major change in our findings. Indeed, among various immigrant groups, Russian immigrants have been shown to have some of the highest proportions of health insurance.³⁹ The qualitative research of local Russian-speaking groups referenced above suggests that the decreased vaccination we observed is indeed driven by vaccine hesitancy and refusal.²²