Vaccine Schedule Not Followed for One Third of Children in US

Just over one third of US children are not vaccinated according to the childhood immunization schedule recommended by the Centers for Disease Control and Prevention (CDC), according to a study published online today in Pediatrics.

Fewer than 6 in 10 children whose parents responded to the 2014 National Immunization Survey (NIS) had received all recommended vaccines by age 19 months to 35 months. The choice to delay receipt of one or more vaccines increased children's likelihood by fourfold of not being up to date with recommended vaccinations.

"The nonadherence of nearly 40% of the children in the 2014 NIS to the recommended schedule is consistent with several trends reported by American doctors in recent years, including parental requests to limit the number of vaccinations given at each visit, increased need for a strong and consistent physician recommendation for vaccination, and potentially wavering vaccine confidence," write Allison L. Hargreaves, MPH, from the California Department of Public Health, Office of AIDS, in Sacramento, and colleagues.

"The findings in this study reaffirm that deviations from the recommended immunization schedule, whether as the result of parents following an alternate schedule or other factors, result in many children remaining out-of-date for an extended period of time," write Hargreaves, who was previously of Emory University in Atlanta, Georgia, and colleagues.

More Vaccine Visits, Less Protection

Even among children vaccinated on a nonstandard schedule who were up to date by 35 months old, delaying some vaccines led to an average of three additional vaccination office visits — 10 instead of 7 — compared with the number of visits for children vaccinated according to the CDC-recommended schedule.

Those extra visits put additional burdens on families and on the healthcare system, senior author Robert A. Bednarczyk, PhD, told Medscape Medical News.

Most concerning, those delays leave children unprotected against vaccine-preventable diseases for longer than necessary, said Bednarczyk, who is an assistant professor of global health and epidemiology at Emory University.

"It's great that some of these children are getting caught up on all of their vaccines even after some initial delays," he continued. But "outbreaks can occur without a lot of warning, so you're still leaving children vulnerable to vaccine-preventable diseases when they're younger, when [infections] could potentially be more severe."

Three Main Vaccination Patterns

The researchers analyzed the complete data set from the 2014 NIS, which included de-identified vaccination records of 15,059 children in all 50 states and Washington, DC. The 2014 NIS was the most recent data set available at the study's initiation and included children's ages (in days) when they received each vaccine.

The authors identified three main vaccination patterns by examining which vaccines children received in each of five age ranges: birth (0-30 days), 2 months (38-92 days), 4 months (66-153 days), 6 months (94-214 days), and 12-19 months (361-580 days). The three patterns included following the recommended schedule, following an "alternate" schedule (delayed or selective), or being unclassifiable as recommended or alternate.

Children vaccinated on the recommended schedule received all age-appropriate recommended vaccines during at least four vaccination visits through 19 months old, with no more than six total vaccination visits.

Children vaccinated on a "restrictive" (delayed) alternate schedule had at least six vaccine visits during which they received no more than three vaccines per visit. Children on a "selective" alternate schedule did not receive a single dose of at least one vaccine type. Children who never received at least one vaccine and never received more than three vaccines per visit were classified as restrictive and selective.

Unclassifiable children did not follow a clearly discernible schedule.

The authors then compared the association between these patterns with being fully up to date with all recommended vaccines at 19-35 months old. The CDC's definition of being up-to-date currently excludes hepatitis A and rotavirus vaccines, the two most recent additions to the recommended schedule for infants, but the authors chose to include both to achieve a more comprehensive picture of adherence to the schedule.

Fewer Children Up-to-date

Overall, 58% of children were fully up-to-date with all vaccines recommended by the CDC's Advisory Committee on Immunization Practices by 19-35 months old. (This number is lower than the CDC's official up-to-date percentage of 71% for the 2014 NIS because the CDC excludes hepatitis A and rotavirus vaccines.)

The 23% of children who were vaccinated on an alternate schedule were over four times more likely not to be fully up-to-date on vaccinations (prevalence ratio [PR], 4.2), compared with the 63% who were vaccinated according to the schedule.

The 14% whose vaccination pattern was unknown or not classifiable were more than twice as likely not to be up-to-date (PR, 2.4).

None of the children vaccinated on a selective schedule were up to date as, by definition, they had never received at least one recommended vaccine.

"Children who moved across state lines, were not firstborn, lived in the Northeast (versus the South), and were non-Hispanic black or multirace below the poverty level (versus non-Hispanic white above poverty) were more likely to follow an alternate vaccination pattern compared with the recommended schedule," the authors report.

"Children who received WIC benefits, were living below poverty, moved across state lines since birth, and received vaccinations from public facilities only (versus private providers) were more likely to be in the unknown or unclassifiable schedule category, compared with the recommended schedule."

Being up-to-date overall was not associated with any sociodemographic characteristics, but the demographic associations with vaccination patterns remain worthy of deeper investigation, Bednarczyk told Medscape Medical News. The associations found with the unclassifiable category in particular suggest that parents may intend to follow the recommended schedule but encounter logistical barriers or other circumstances that interfere, he said.

"One of the biggest limitations of this study is that we don't have a sense of why individuals were vaccinated on the patterns that they were vaccinated," Bednarczyk said. "We don't know if it was due specifically to hesitance or to logistics or some other consideration." Additional research that can begin to unpack the associations identified in this study can help in determining the different strategies needed to improve vaccine coverage, he added.

In the meantime, Bednarczyk suggested that doctors and nurses may be able to alleviate the concerns of some parents who want to delay or skip some vaccines by explaining the rigorous process by which the CDC-recommended schedule is developed. The CDC's Advisory Committee on Immunization Practices reviews the childhood immunization schedule every year and tweaks it as needed based on the most recent data.

Understanding that process and level of review, physicians and nurses can "use those facts in their conversations with parents to let them know this is a schedule that's designed to provide the greatest level of protection at the earliest possible ages," Bednarczyk said.

No current data are able to quantitatively estimate the level of increased risk of vaccine-preventable illnesses among children who follow a delayed vaccination schedule but ultimately get caught up. But the delays do leave those children susceptible to diseases for a longer period of time, Bednarczyk said. Most of the children who contracted measles or pertussis in recent US outbreaks were unvaccinated or only partially vaccinated relative to how many vaccines they should have had, he said. And data have shown that early delays in vaccination and vaccine refusal are having essentially the same effect.

The research was funded by the National Vaccine Program Office and senior author's National Institutes of Health grant. The authors had no disclosures.

Pediatrics. 2020;145:e20190783. Abstract

Tara Haelle is an independent health and science journalist and book author. She specializes in reporting on vaccines, pediatrics, women's health, mental health, and medical research. Follow her on Twitter: @tarahaelle.

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