MHLU - Health Status Resource

Immunization Coverage

Immunization Coverage

Key Findings: 

Ontario public health units have a mandate to “reduce or eliminate the burden of vaccine preventable diseases through immunization”.1 One way that public health units address this mandate is by assessing immunization coverage rates among students, which is legislatively supported through the Immunization of School Pupils Act (ISPA). Another way is by monitoring seasonal influenza immunization coverage among staff at long-term care homes (LTCH) and hospitals.

Across the range of vaccine preventable diseases and from students to care-providers, immunization is well established within Middlesex-London. However, there are still improvements to be made in immunization coverage that will advance coverage goals and provide population-level protection from vaccine preventable diseases.

Childhood immunization coverage School-based immunization coverage
Adolescent immunization coverage Long-term care home and hospital staff influenza immunization coverage

Childhood immunization coverage

Immunization coverage among 7-year old students enrolled in Middlesex-London schools increased between the 2013/14 and 2016/17 school years for diphtheria, meningococcal C, pertussis (whooping cough), polio, tetanus, and varicella (chickenpox). The most marked increase over the four-year period was for varicella coverage, from 24.6% to 61.0%. During the same time period, immunization coverage decreased for measles, mumps and rubella (Figure 10.1.1).

In the 2016/17 school year, immunization coverage among 7-year old students in Middlesex-London schools was higher than in Ontario for diphtheria, pertussis, polio, tetanus, and varicella. Immunization coverage was lower among students in Middlesex-London schools than in the province as a whole for measles, meningococcal C, mumps, and rubella. However, local coverage for all diseases was lower than the national target of 95% coverage (Figure 10.1.2).

Interpretation:

While immunization coverage for diphtheria, meningococcal C, pertussis, polio, tetanus, and varicella all increased between the 2013/14 and 2016/17 school years among 7-year olds students in Middlesex-London, coverage in the most recent school year was lower than the national target of 95% for all diseases. This means that immunization coverage among 7-year old students was less than optimal to provide population-level protection should any of these diseases be introduced into the Middlesex-London region.

Among 7-year old students, the decrease in immunization coverage for measles, mumps and rubella between the 2013/14 and 2016/17 school years may be partially due to a change in the Publicly Funded Immunization Schedules for Ontario. Immunization against these three diseases is usually given in one vaccine (MMR). Previously, a routine second dose of MMR vaccine was administered at 18 months of age as part of the infant immunization series. Since August 2011, the routine second dose of MMR-containing vaccine was shifted to be given at 4- to 6-years of age, and therefore may have been more easily overlooked by parents or health care providers until immunization record screening by Ontario public health units.

Although immunization against measles, mumps, and rubella is usually given in the same vaccine, coverage for rubella among 7-year old students was higher than for measles and mumps. This is because only one dose is necessary to be considered up-to-date for rubella, whereas two doses are required for measles and mumps.

The increase in varicella immunization coverage among 7-year old students may also be associated with changes to the Publicly Funded Immunization Schedules for Ontario. Since August 2011, two doses of varicella-containing vaccine are publicly funded, rather than only one dose. The increase in immunization coverage may correspond to increased awareness among parents and health care providers of the updated requirement for two doses of varicella-containing vaccine. Coverage is expected to further increase as of the 2017/18 school year, since the ISPA requires all students born in 2010 (the birth cohort who will be 7 years old in that school year) or later to be up-to-date for two doses of varicella-containing vaccine.

Adolescent immunization coverage

Immunization coverage among 17-year old students enrolled in Middlesex-London schools remained relatively stable or decreased between the 2013/14 and 2016/17 school years for all diseases except pertussis, which fluctuated between 66.8% and 75.0% across the four-year time span (Figure 10.1.3).

In general, immunization coverage for measles, mumps, polio and rubella among 17-year old students was 94.0% or higher regardless of the year. However, coverage for diphtheria, pertussis, and tetanus was much lower, ranging from approximately 67.0% to 80.0% (Figure 10.1.3).

In the 2016/17 school year, immunization coverage among 17-year olds in Middlesex-London schools was higher than Ontario coverage for diphtheria, measles, mumps, pertussis, polio, rubella, and tetanus. Further, local immunization coverage met the national target of 95% for measles, mumps and rubella. Coverage for diphtheria, pertussis, polio, and tetanus was lower than the national targets (Figure 10.1.4).

Interpretation:

Among 17-year old students, local immunization coverage against measles, mumps, and rubella met the national target of 95% in all years between the 2013/14 and 2016/17 school years, suggesting that immunization coverage among this group of students was sufficient to provide population-level protection.

Coverage for diphtheria, pertussis, and tetanus among 17-year old students in Middlesex-London schools was relatively low across the four-year time period, ranging from 67.0% to 80.0%. Immunization against these three diseases is typically administered in one vaccine, with a dose due to be given between 14- and 16-years of age, according to the Publicly Funded Immunization Schedules for Ontario. However, this dose may be overlooked until immunization record screening of high school students by Ontario public health units.

Although adolescent immunization against diphtheria, pertussis, and tetanus is typically administered in one vaccine, there is an alternative product providing protection against only diphtheria and tetanus that is offered to adults approximately every ten years. This may account for pertussis immunization coverage among 17-year old students being lower than diphtheria and tetanus, as some health care providers may administer the diphtheria- and tetanus-containing vaccine to adolescents, rather than the vaccine that also protects against pertussis.

School-based immunization coverage

Ontario public health units offer vaccines through school-based clinics that protect against hepatitis B, human papilloma virus (HPV), and four strains of meningococcal disease (ACYW-135). Between the 2013/14 and 2016/17 school years, immunization coverage for the school-based meningococcal vaccine increased from 70.6% to 76.5% among 12-year olds in Middlesex-London schools. However, local up-to-date immunization coverage for both hepatitis B and HPV decreased over the same time period, from 64.2% to 59.9% for hepatitis B, and from 52.6% to 50.7% for HPV. (Figure 10.1.5).

In the 2016/17 school year, immunization coverage among students in Middlesex-London schools was lower than coverage across the province as a whole for hepatitis B, HPV, and meningococcal ACYW-135. Local coverage for these diseases was also lower than the national target of 90% (Figure 10.1.6).

Interpretation:

In general, immunization coverage for hepatitis B, HPV, and meningococcal ACYW-135 was lower among Middlesex-London students than coverage across the province as a whole, as well as the national target of 90%. The low uptake of these vaccines may be partially due to student or parent hesitation about receiving these vaccines. This reinforces the need for ongoing education about and promotion of these important immunizations.

Long-term care home and hospital staff influenza immunization coverage

Ontario public health units support long-term care homes (LTCH) and hospitals to promote seasonal influenza immunization uptake among staff, and to monitor coverage each season, as one measure to decrease the risk of influenza transmission among LTCH residents and hospital patients. With the exception of the 2017/18 season, the influenza immunization coverage estimate was higher among LTCH staff than those in hospitals, in both Middlesex-London and Ontario (Figure 10.1.7).

Between the 2003/04 and 2017/18 influenza surveillance seasons, seasonal influenza immunization coverage estimates for Middlesex-London LTCH and hospital staff fluctuated depending on the season. The influenza immunization coverage estimate among LTCH staff in Middlesex-London facilities decreased from 88.6% in 2003/04 to 55.2% in 2017/18. Since the 2014/15 season, coverage among LTCH staff has consistently decreased and has been lower than the provincial estimate since the 2016/17 season (Figure 10.1.7).

Overall, the influenza immunization coverage estimate among staff in Middlesex-London hospitals increased between the 2003/04 and 2017/18 seasons, from 48.0% to 57.3%, and has exceeded the Ontario estimate since the 2012/13 season. However, coverage among Middlesex-London hospital staff has consistently decreased since the 2013/14 season (Figure 10.1.7).

Interpretation:

A marked decline in seasonal influenza immunization coverage among LTCH and hospital staff was observed in the 2009/10 influenza surveillance season across the province and in Middlesex-London facilities. The 2009/10 season was anomalous in that pandemic influenza A(H1N1) began spreading worldwide in the spring of 2009, and was widely circulating in the Middlesex-London region by fall 2009. Although a seasonal influenza vaccine was available in October 2009, staff at LTCH and hospitals may have elected to not receive seasonal influenza vaccine because it did not offer protection against the pandemic influenza A(H1N1) strain that was known to be circulating in the region.

Although influenza immunization among staff at LTCH and hospitals in the Middlesex-London region is an important means to help prevent influenza transmission in these facilities, staff coverage estimates in both settings have declined in recent seasons. This suggests that new approaches to promoting influenza vaccine uptake among LTCH and hospital staff may need to be explored, and other strategies to prevent the transmission of influenza in these facilities may need to be enhanced.
Interpretive Notes

For childhood and adolescent immunizations, the number of vaccine doses required to be up-to-date varies depending on the disease and the age of the child. These differences may result in varying up-to-date immunization coverage for diseases where a single vaccine provides protection against more than one disease. For example, immunization against measles, mumps, and rubella is usually given in one vaccine. Two doses are required to be up-to-date for measles and mumps, whereas only one dose is required for rubella. As a result, immunization coverage for rubella is typically higher than for measles and mumps, even though protection against all three diseases is provided in one vaccine.

The publicly funded eligibility criteria to receive human papilloma virus (HPV) vaccine has changed over time. Prior to the 2016/17 school year, only 13-year old females were eligible to receive publicly funded HPV vaccine. In the 2016/17 school year, the program was changed such that 12-year old students, both females and males, were eligible, as well as 13-year old females. Figures showing up-to-date coverage for HPV reflect all who were eligible in the specified school year.

Ontario Public Health Standard: 

Ontario Public Health Standards: Requirements for Programs, Services, and Accountability – Immunization (pages 39-40)

Population Health Assessment and Surveillance Protocol, 2018

References:

1. Ontario Ministry of Health and Long-Term Care. Protecting and Promoting the Health of Ontarians - Ontario Public Health Standards: Requirements for Programs, Services, and Accountability [Internet]. Toronto, ON: Queen’s Printer for Ontario; 2018 [cited 2019 Feb 12] 75p. Available from: http://www.health.gov.on.ca/en/pro/programs/publichealth/oph_standards/d...

2. Agency for Health Protection and Promotion (Public Health Ontario). Immunization coverage report for school pupils in Ontario: 2016-17 school year [Internet]. Toronto, ON: Queens’s Printer for Ontario; 2018 [cited 2019 Feb 12] 65p. Available from: https://www.publichealthontario.ca/-/media/documents/immunization-covera...

Last modified on: May 6, 2019

Jargon Explained

Immunization coverage:
“Immunization coverage refers to the proportion of a defined population that is appropriately immunized against a specific vaccine-preventable disease (VPD) at a point in time”.2

Student immunization coverage is usually expressed as a percent, and can be calculated for a variety of populations of interest: within a particular grade in a school, for an entire school, or across an entire region. As immunization coverage values increase, the greater the proportion of people in the population of interest who are appropriately immunized, and therefore considered to have protection from the vaccine-preventable disease of interest.

Assessment of whether or not students are appropriately immunized is based on whether they have received the immunizations indicated in the Publicly Funded Immunization Schedules for Ontario at the appropriate age and time intervals.

Immunization of School Pupils Act:
The Immunization of School Pupils Act (ISPA) is the Ontario legislation that outlines the responsibilities of Ontario public health units to maintain immunization records for students attending schools in their jurisdictions, and to assess those records to ensure that students are appropriately immunized against designated vaccine-preventable diseases of public health significance. Under the ISPA, students whose immunization records are not up-to-date for designated diseases may be suspended from school. Those who have had the disease of interest or who have medical reasons for being unimmunized against ISPA-designated diseases can submit a Statement of Medical Exemption. Those who have philosophical or religious reasons for being unimmunized can submit a Statement of Conscience or Religious Belief.

Median
The median is a measure of central tendency used to describe data. The median of a set of values is calculated by first ordering the values from smallest to largest; the median is the middle number of the ordered values. One-half of the values in the set are above the median, and one-half of the values are below the median.

Publicly Funded Immunization Schedules for Ontario
The Publicly Funded Immunization Schedules for Ontario is maintained by the Ontario Ministry of Health and Long-Term Care. It outlines a variety of vaccines that are to be offered to all eligible Ontarians at no charge, and articulates the appropriate age and time intervals at which to receive each vaccine. The Publicly Funded Immunization Schedules for Ontario is used to assess whether a student is appropriately immunized for the purposes of the ISPA.