Up to a tenth of parents of infants in Portland, Ore., consistently strayed from recommended vaccination schedules, and health providers accommodated them, according to findings of a cohort study.
The children of consistently shot-limiting parents were less likely to be caught up at either 9 or 19 months, the study also found.
Steve G. Robison, epidemiologist for the Oregon Health Authority’s immunization program, and his colleagues, conducted a retrospective analysis of immunization records for 97,711 children born between 2003 and 2009, published online June 18 in Pediatrics (2012;130:32-38 [doi:10.1542/peds.2011-3154]).
"Many parents have heard a lot of opinions about immunizing young children. We looked to see if parents were actually following alternative immunization schedules," Mr. Robison said in an interview.
In the cohort, 4.6% of children had received no more than two vaccine injections in a single immunization visit from birth to 9 months, a practice promoted by at least two physician authors of books aimed at parents. Episodic limiters, by contrast, were defined as having at least one visit in which the number of shots was limited, and only one or two visits with three or more injections, by 9 months.
The proportion of consistent shot limiters in the cohort increased from 2.4% to 9.5% between 2006 and 2009, the study found. Episodic limiters increased from 19.5% to 30.1% in the same period.
The study showed that the consistent shot limiters had fewer shots on average by 9 months than did those consistently adhering to or episodically limiting adherence to recommended schedules (6.4 vs. 10.4), but more provider visits (4.2 vs. 3.2). This likely means that physicians have been accommodating parents’ desires to vaccinate differently, and ultimately less, than is recommended by the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices.
At 9 months, the consistent shot limiters were significantly less likely to be caught up for any immunization series than nonlimiters or episodic limiters, with an average relative risk (RR) of 0.55. By 19 months, the risk was attenuated for vaccinations due by 9 months (average RR, 0.72). However, the gap was again seen for vaccination due by 19 months (average RR, 0.54). For varicella, hepatitis A, or MMR in particular, consistent limiters were less likely on average to have received these at 19 months (average RR, 0.48) than episodic or nonlimiters.
"Kids with limited shots also had more visits to doctors for shots," Mr. Robison said. "This is what some alternative immunization schedules tell parents to do – to take their babies in almost every month for a shot in their first year of life. But these kids got fewer shots."
Recent national studies have shown trends toward increasing parental adoption of alternative vaccination schedules, with reports of between 13% and 21.8% of parents intentionally following alternative schedules that delay or limit vaccination (Pediatrics 2011;128:848-56 and Public Health Rep. 2010;125:534-41). Mr. Robison and his colleagues found that between 2004 and 2009, episodic and consistent limiters constituted between 24.9% and 39.6% of the Portland cohort.
Although the Portland study showed a higher proportion of limiters than did earlier studies, "we do not know if it can be generalized beyond the Portland area and certainly hope not," Mr. Robison said in an interview. The study population, he pointed out, has high vaccine exemption rates for school entry and may not be representative on a national scale.
Mr. Robison’s study also found that although two physicians have published immunization schedules deviating from ACIP recommendations, the consistent shot-limiting parents were not adhering closely to those alternative schedules. However, their tendency to have avoided certain types of shots by 19 months – particularly varicella, hepatitis A, or MMR – seemed to be consistent with the ideas promulgated by these authors.
"Dr. Stephanie Cave’s 2007 schedule specifies a total of five visits at 4, 5, 6, 7, and 8 months, and Dr. Robert Sears’s ‘Alternative Vaccine Schedule’ suggests a total of six visits at 2, 3, 4, 5, 6, and 7 months. Both Dr. Cave and Dr. Sears specify avoidance of HepB vaccines in the first 2 years of life, unless the birth mother is HepB surface antigen positive. Other specifics of Dr. Cave’s schedule, reissued in 2007, include entirely avoiding the rotavirus vaccine and delaying the pneumococcal vaccine until the second year of life. According to Dr. Sears’s schedule, infants would receive all recommended vaccines by 9 months of age except for the HepB and the polio vaccine," Mr. Robison and his colleagues related.
"There are no known benefits to delaying or spacing out shots this way," Mr. Robison said. "On the other hand, there are extra costs and time for a parent to take their kid in to the doctor. It’s also easy for a baby on an alternative schedule to fall behind and not catch-up."