Characterization of Heterogeneity in Childhood Immunization Coverage in Central Florida Using Immunization Registry Data
by Kimberly M. Thompson, Grace E. Logan, and the Research Team from Florida SHOTS™, Risk Analysis 2016; 36(7):1418-26 (published on-line June 2, 2015, doi: 10.1111/risa.12424)

Answers to frequently asked questions

What are the study’s main findings?
What are the study’s main recommendations?
What challenges arose in the analysis?

What are the study’s main findings?

• This first ever study to use state immunization information system data to characterize differences between immunization records for children by zip code and county demonstrates the important public health contribution of electronic systems that track immunization.
• Data from the Florida SHOTS™ immunization information system for records with a zip code in one of 6 Central Florida counties (Brevard, Lake, Orange, Oseola, Polk, and Seminole) at high risk for importation of vaccine-preventable diseases because of popular international family attractions in the area, suggest that most children born January 2003 - December 2014 benefit from protection from: diphtheria–pertussis–tetanus (DPT), inactivated poliovirus (IPV), measles–mumps–rubella (MMR), hepatitis B (HEPB), Haemophilus influenzae type b (HIB), pneumococcal conjugate (PNE), varicella (VAR), and meningococcal (MNG) vaccines.
• Analysis of the data by zip code show relatively low rates of religious exemptions (fewer than 3.5% of children in every zip code). Zip codes in Seminole County and in eastern Brevard County show the highest proportions of children with religious exemptions, with exemptions in the records of approximately 1.5% of children overall in Seminole County and in ≤ 0.8% of the records of children overall in each of the other five counties. The study provides county health departments and schools with maps that may prove helpful with respect to identifying zip codes at relatively higher risk.
• Some children with religious exemptions receive some immunizations, although the presence of an exemption in the record represents a clear risk factor for under-immunization, and any unvaccinated individuals remain at risk of infection throughout their lives.
• Some zip codes include more than 1000 children born January 2003 - December 2014 with no record of receiving one or more of the 8 vaccine series analyzed. This may suggest potential risk for transmission of some diseases, although the data remain limited due to incomplete records that do not include some immunizations received due to the gradual adoption of Florida SHOTS™ during the time period.
• Recent outbreaks of measles in and around Central Florida demonstrate the significant and real risk of importation, with unimmunized individuals becoming infected and spreading the virus. In 2012, an infected tourist from Brazil who visited a Central Florida theme park led to a limited outbreak of measles with 4 cases reported in early 2013 involving 4 unvaccinated siblings.  Small measles outbreaks in 2015 in Indian River County involving 3 unvaccinated family members (including one adult who became infected during international travel and subsequently infected household members) and in St. Lucie County involving 2 unvaccinated siblings provide evidence of continued importations. Both of these counties lie south of Brevard County (i.e., outside the 6 counties studied).
• The relatively limited outbreaks in Central Florida contrast with the larger measles outbreaks in Orange County, California in early 2014 and that began in December 2014 with 42 cases linked to exposure at Disney theme parks in Anaheim, CA and ended in mid-April 2015 with 131 cases reported in California residents and epidemiologically-linked cases reported from 6 other states, Mexico, and Canada. In contrast to Florida, California allows personal belief exemptions, which leads to higher overall exemptions in counties with theme parks near Orange County, California than in comparable counties in Orange County, Florida:

  California	Exempt	Florida	Exempt
  Los Angeles	1.6%	Brevard	0.8%
  Orange	2.7%	Orange	0.7%
  San Diego	3.2%	Polk	0.8%

  Note: Florida estimates from religious exemption data analyzed in this study. California estimates based on the average of annual kindergarten-reported personal belief exemptions for years 2007-8 through 2014-5, which approximately corresponds to children born 2003-2010 and may underestimate actual overall rates if exemptions in California increased for children born 2010-2014.
  Back to questions

• Ensure that you and your family receive all indicated immunizations on time and according to the vaccination schedule, and if necessary, get caught up on any missed immunizations - it's not too late to vaccinate. The catch-up immunization scheduler provides a tool to help identify missed childhood immunizations. Unimmunized and underimmunized individuals remain at risk of becoming infected at any point in their lives due to importations, which can occur anytime and anywhere unless and until global eradication (for those diseases that can be eradicated, including polio, measles, and rubella).
• If planning to travel internationally, make sure you receive necessary immunizations. Remarkably, despite a regional goal to eliminate measles and rubella transmission in Europe by 2015, many importations of measles into the US in recent years involved importations from Europe.
• Florida residents should ensure that records for their families in Florida SHOTS™ reflect updated, current, and complete information and/or schedule an appointment with a health care provider or the county department of health to review your immunization records.
• Florida health care providers should check immunization records in Florida SHOTS™ and ensure the records contain correct and complete information.
  Back to questions

• Immunization information systems like Florida SHOTS™ are relatively new, and their adoption by health care providers in different areas occurred gradually, which leads to some incomplete records, particularly for older children and highly mobile populations. This study analyzed the data cross-sectionally and included all records in the system for children born January 2003 - December 2014 with a zip code in one of the 130 zip codes identified for the 6 counties, which included some records with only one reported vaccine dose delivered. While we excluded records of children known to have moved out of the area or died, and we may have missed some children residing in the area but not accessing the health system, this analysis implicitly assumes that individuals that remained in the set of records analyzed with no reported doses for some vaccines did not receive those vaccines and that they still reside within the zip code. This cumulative analysis leads to characterizations that present more of a worst-case scenario for overall estimates of children on-track for specific vaccines and for estimates of numbers of children without any protection from specific vaccines, which led us to focus on the relative comparisons between zip codes and counties instead of on absolute numbers. Improved reporting will help to provide better quality data for future analyses.
• The methods in this study contrast with an important recent study of a cohort of children served by a large health maintenance organization in northern California that could ensure that it analyzed data only from the insured children it covered from birth to 36 months and for which it would have most likely been the sole immunization provider, which offers more of a best-case scenario approach. We cannot make direct comparisons between the results of our study with this study.
• The methods in this study also contrast with school level analyses that may include individuals concentrated within a zip code (i.e., narrower scale) and/or individuals who commute from multiple zip codes (i.e., broader scale). Schools and child care centers continue to represent the primary mixing locations for children to spread infectious diseases, but as recent experience shows, any crowded area that brings unimmunized individuals together can facilitate spread. Different types of analyses provide complementary information, but all of the studies suggest risks associated with under-vaccinated individuals.
• Efforts to link immunization information system data across states may help future studies address issues related to the inclusion of individuals who move between states and whose records in any one area provide incomplete data. In the absence of such a system and without a means to easily verify the current residence location of individuals with records in the system, the data remain limited.
  Back to questions