Study Shows Immunization-Medicaid Correlation

New Mexico has the highest proportion of children in the nation enrolled in Medicaid. An article published in the Public Library of Science journal PLoS One highlights research showing that childhood immunization rates in the state suffered when barriers increased to children’s receiving Medicaid coverage.

Researchers at the University of Toronto, University of New Mexico, and New Mexico Department of Health conducted the study. Dr. Michael Schillaci from the Department of Social Sciences at the University of Toronto, Scarborough, and his colleagues analyzed immunication and Medicaid enrollment statistics for New Mexico between 1996 and 2006.

The article’s authors argue that ensuring childhood access to Medicaid enrollment actually is more important for immunizing New Mexico’s children than are the benefits provided by programs that focus narrowly on improving immunization practices.

Their study revealed a strong correlation between immunization rates and Medicaid enrollment among those receiving financial support through the Temporary Assistance for Needy Families (TANF) program. When Medicaid enrollment increased, so did childhood immunization rates (see figure).

In 2004, the state government decided to require recertification for Medicaid every six months and to close automatically Medicaid cases that did not complete the eligibility certification process. These policy changes led to lower Medicaid enrollment levels. Overall Medicaid enrollment in New Mexico decreased by approximately 4.7%, by far the largest drop during that time period in the nation.

The 2004 reduction in TANF Medicaid enrollments was associated with a similar reduction in immunization rates.

One of the authors of the study, Dr. Howard Waitzkin from the University of New Mexico, explained: “The results of the study show that state-level changes in Medicaid policy can have unanticipated consequences on the delivery of preventive care. Barriers to public insurance coverage under Medicaid overshadowed New Mexico’s laudable campaign to improve immunizations.”

Because childhood immunizations are tied to well-child visits, a change in immunization rates may indicate a change in the level of early childhood preventive care.

Due to New Mexico’s high proportion of children enrolled in Medicaid, policy changes that reduce Medicaid enrollment also reduce the likelihood that primary care practitioners will provide adequate preventive care, including immunizations.

For more information or contact with the authors, please call Howard Waitzkin at 505-277-0860, or Michael Schillaci at 416-287-7328, or send an email message to or

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