Vaccine uptake in Canadian adults: Results from the 2014 adult National Immunization Coverage Survey (aNICS)

Key Findings

  • National immunization coverage targets for adulthood vaccines were not met among the general Canadian population, those at high risk for severe complications associated with vaccine-preventable diseases and healthcare personnel.
  • While most individuals believed that they received all vaccines required for someone their age, less than 10% were up-to-date on their adult immunizations.
  • More effort is required to increase adult immunization coverage in Canada, especially among high risk groups.

Introduction

Immunization is a major accomplishment for public health, effectively preventing infectious disease and improving the health of Canadians. While most routine immunizations are provided during childhood, vaccinations are recommended in adulthood as well. Immunizations are important for adults for the following reasons:

  • immunity against certain vaccine-preventable diseases wanes over time and requires boosting (e.g. tetanus)
  • certain vaccine-preventable infections are more virulent in adults and can cause serious disability and death (e.g. varicella)
  • adult immunization helps establish immunity against certain diseases that are more common in adulthood (e.g. herpes zoster, also known as shingles)
  • adult immunization helps prevent infection and therefore protect vulnerable people who cannot be immunized, are not yet fully immunized or are unable to build strong immunity to vaccines. This includes young infants, vulnerable patients in hospitals or institutions, and those with immune-compromising conditions such as cancer or human immunodeficiency virus (HIV).

Since 1991, the Public Health Agency of Canada has been monitoring national immunization coverage for select adult vaccinations Footnote 1. Beginning in 2001, the adult National Immunization Coverage Survey (aNICS) has been conducted approximately every two years. Results from aNICS are used to monitor national coverage levels for the vaccines recommended by the National Advisory Committee on Immunization (NACI) Footnote 2, to report immunization coverage estimates to international organizations and to develop appropriately targeted public education strategies. Immunization coverage for seasonal influenza, pneumococcal, hepatitis B, tetanus, and acellular pertussis vaccines is measured in the general, non-institutionalized adult population (18 years of age and older). Coverage is also reported for specific target groups recommended by NACI, which includes seniors aged 65 years and older, adults aged 18 to 64 years with chronic medical conditions, and healthcare professionals. Furthermore, varicella immunization coverage is measured in adults under 65 years of age who reported not having had varicella infection (chickenpox) as a child, and human papillomavirus (HPV) immunization coverage is measured in adults aged 45 years and under. The aNICS is also used to assess adults' knowledge and attitudes regarding vaccines and identify needs for additional information relating to adult immunization.

The aNICS was conducted in 2001, 2006, 2008, 2010, 2012 and 2014. This report details the survey results from the 2014 cycle.

Methodology

Questionnaire

The questionnaire was developed in consultation with immunization experts across Canada. NACI-recommended target groups were identified including: individuals aged 65 years and older, adults aged 18 to 64 years with chronic medical conditions, and healthcare personnel (defined as individuals working or volunteering in a healthcare setting). Respondents were surveyed on the acceptability of immunization and on whether they have enough information about the benefits of immunization. The survey also included demographic questions on age, gender, education, employment status, household income, and country of birth.

All respondents were asked if they had received the seasonal influenza vaccine in the past year; ever vaccinated against hepatitis B; ever received a dose of pertussis-containing vaccine in adulthood; and if they had received a tetanus vaccine in the last 10 years. In addition to the above items, individuals under 65 years of age were also asked if they had ever been vaccinated against varicella, and those 45 years-old and younger were asked about immunization against HPV. Pneumococcal vaccine uptake was asked in respondents 65 years of age or older and adults with chronic medical conditions.

Sampling

Respondents from every province and territory were selected using random digit dialing (RDD) which included land lines and known cellphone-only household numbers. Sampling was stratified by province/territory and community size. The sample was then weighted to be nationally representative using data from the 2011 Canadian Census Footnote 3.

In addition to RDD, individuals working in a healthcare setting were identified from the MD Select (published by Scott's Info Medical) for physicians and Dun & Bradstreet Canada national database for other healthcare occupations. Relevant healthcare organizations were selected from the Dun & Bradstreet database, and then contacted to identify eligible respondents.

Data Collection

The 2014 aNICS was conducted by telephone between September and October 2014 by the Environics Research Group. Those who agreed to participate in the survey were asked about their previous immunizations based on memory recall. Respondents were screened during the telephone interview and categorized within the target groups: adults 65 years of age and older,  Canadians 18 to 64 years-old with chronic medical conditions, and healthcare personnel. Chronic medical conditions were defined as those at increased risk for severe complications from influenza and/or pneumococcal infection as determined by NACI Footnote 4.  This includes heart conditions, asthma, other chronic lung condition, cancer, diabetes, liver cirrhosis, chronic kidney disease, immune disorder/suppression, asplenic/problem with the spleen, or hemoglobin problem.

Statistical Analysis

National coverage estimates for each recommended adult vaccine were calculated as the number of positive responses (i.e. having received the vaccine) expressed as a percentage of the sum of positive and negative responses (excluding those who did not know or declined to respond). Estimates were weighted to represent the Canadian population in terms of age, gender and region size, using information from the 2011 Census Footnote 3. National data for healthcare professionals were weighted by age and region. Coverage estimates were stratified by target groups for certain vaccines.

Results

The response rate for adults in the general population (i.e. recruited through RDD) was 11%, and 13% among the list-based sample for healthcare personnel. Overall, 3,290 adult respondents completed the interview by telephone, with 3,040 participants recruited through RDD and an additional 250 healthcare personnel from targeted databases. In total, 565 healthcare personnel participated in the survey (315 through RDD and 250 from list-based sampling).

In the general adult sample (n=3040), 52% were female and 19% were born outside Canada. The median age was 48 years (range 18 - 97 years) with 17% being 65 years of age and older. There were 715 Canadians aged 18 to 64 years of age with a chronic medical condition (31%). Most participants had some postsecondary education (34%) or had completed university (38%), and a quarter of the sample had an annual household income greater than $100,000 before taxes.

Among the sample of healthcare personnel (n=565), the median age was 46 years (range 19 - 94 years) and most were female (77%). The most common occupations included nurses (31%), physicians (12%), nursing assistants (10%) and administrators (10%). The majority of healthcare personnel (70%) reported having close contact (within one meter) with patients or residents.

The estimated immunization coverage for influenza, tetanus, pertussis and pneumococcal vaccines among adults and healthcare personnel are summarized in Table 1.

Table 1. Coverage for influenza, tetanus, pertussis and pneumococcal vaccines among adults and healthcare personnel, Canada, 2014
Participants n Vaccine coverage (%) for at least one dose (95% confidence interval)
InfluenzaTable 1 - Footnote TetanusTable 1 - Footnote PertussisTable 1 - Footnote § PneumococcalTable 1 - Footnote ǁ
Adults (≥ 18 years) 3040 40.3 (38.3, 42.3) 49.5 (47.4, 51.7) 9.3 (8.1, 10.5) -
18-64 years of age with a chronic medical conditionTable 1 - Footnote *
715 43.8 (39.6, 48.1) 51.4 (47.1, 55.8) 8.4 (6.0, 10.8) 17.3 (13.7, 20.8)
≥ 65 years of age
831 67.1 (63.4, 70.7) 38.0 (34.1, 41.9) 8.9 (6.5, 11.2) 36.5 (32.7, 40.3)
Healthcare personnelTable 1 - Footnote 565 69.2 (64.6, 73.9) 68.3 (63.7, 72.8) 23.0 (18.7, 27.2) -
Close contact with patient or resident (within one meter)
394 75.6 (70.8, 80.4) 70.1 (65.0, 75.2) 23.7 (18.6, 28.7) -

i) Seasonal influenza immunization

NACI recommends that all healthy adults receive the seasonal influenza vaccine. In particular, the vaccine is recommended for adults at high-risk for influenza-related complications, those capable of transmitting influenza to high-risk individuals, and those who provide essential community services Footnote 6. All provinces and territories offer publicly-funded seasonal influenza immunization programs to these high-risk groups.

Less than half of the adults (40%) received a dose of the influenza vaccine for the 2013-2014 season. Coverage was the highest among healthcare personnel having close contact with patients or residents (Table 1). As compared with other NACI-recommended target groups, adults with a chronic medical condition had the lowest coverage.

ii) Pertussis and tetanus immunizations

One dose of a pertussis-containing vaccine is recommended by NACI for all adults (18 years of age and older) if not previously immunized during adulthood Footnote 7. For adults, pertussis is given in combination with tetanus and diphtheria as a trivalent vaccine (Tdap) in Canada. This trivalent vaccine has been recommended for adults by NACI since 2003. At the time when the survey was administered, all provinces and territories had implemented a publicly-funded Tdap vaccine program for adults Footnote 8. Less than 10% of the general adult sample reported receiving a vaccine against pertussis in adulthood (Table 1).

For tetanus, NACI recommends that all adults receive a booster dose of tetanus toxoid-containing vaccine every 10 years Footnote 2. Approximately 50% of Canadian adults reported receiving a vaccine against tetanus in the past 10 years (Table 1). Among individuals who have been treated for a wound in the last decade (n=899), 80% (95% confidence intervals [CI] 76.9, 83.1) had a tetanus toxoid-containing vaccine.

iii) Pneumococcal polysaccharide immunization (Pneu-P-23)

NACI recommends one dose of pneumococcal polysaccharide (Pneu-P-23) vaccine for all older adults (65 years of age and older) and adults with chronic conditions that are known to increase risk for invasive pneumococcal disease Footnote 4. The Pneu-P-23 vaccine is publicly-funded for both of these target groups Footnote 8. A greater proportion of older adults (37%) reported having received at least one dose of the pneumococcal vaccine in their lifetime as compared to younger adults (18 - 64 years of age) with chronic medical conditions (17%).

iv) Hepatitis B immunization

The hepatitis B vaccine is recommended by NACI for high-risk groups including healthcare personnel, those who could potentially be in contact with blood or blood products and bodily fluids that may contain the virus, and individuals with certain chronic medical conditions (e.g. chronic liver disease, hemophilia) Footnote 2. While routine hepatitis B immunization programs have been implemented since the mid-1980s, either as infant or school-based programs Footnote 9, not all jurisdictions fund or recommend the vaccine for healthcare personnel.

Estimates on coverage for hepatitis B vaccine among high-risk groups are presented in Table 2.  Healthcare personnel at risk for occupational exposure most frequently reported having received a hepatitis B vaccine as compared to the other target groups (Table 2).

Table 2. Coverage for hepatitis B vaccine among high-risk groups, Canada, 2014
Participants n Coverage (%) for at least one dose of hepatitis B vaccine (95% confidence interval)Table 2 - Footnote *
Adults with chronic liver/kidney disease or a blood disorder 135 45.5 (35.4, 55.7)
Healthcare personnelTable 2 - Footnote ^ 565 72.2 (67.9, 76.5)
Personnel with occupational exposure to blood/bodily fluids, or at risk for needle-stick/surgical blade injury or human bite
407 84.3 (80.3, 88.1)

v) Varicella immunization

NACI recommends that adults under 50 years of age and serologically determined to be susceptible to varicella receive two doses of univalent varicella vaccine Footnote 10. Among individuals under 50 years of age without a self-reported history of varicella (n=118), 35.1% (95%CI 25.2, 44.9) received at least one dose of the varicella vaccine.

vi) Human papillomavirus immunization

The HPV vaccine is recommended for females between 9 and 26 years of age. Since 2010, all provinces and territories have implemented publicly funded HPV immunization programs for pre-adolescent/adolescent girls Footnote 11. The HPV vaccine may also be administered to females between 27 and 45 years of age. As of 2012, males between 9 and 26 years of age are also recommended to receive the vaccine. 

Among females (n=86) and males (n=84) 18 to 26 years of age, 44.7% (95%CI 33.1, 56.3) and 7.6% (95%CI 1.3, 13.9) reported receiving at least one dose of the HPV vaccine, respectively.  Females 27 to 45 years of age (n=436), 8.3% (95%CI 5.3, 11.3) were vaccinated with at least one dose of the HPV vaccine.

vii) Knowledge, attitudes, and beliefs towards immunization

Most adults (88%; 95%CI 86.7, 89.4) and healthcare personnel (92%, 95%CI 89.4, 95.0) believed that immunization is a recognized healthcare practice in their family. Additionally, 77% (95%CI 75.8, 79.4) of adults and 91% (95%CI 88.3, 93.5) of healthcare personnel reported that they knew enough about the benefits of immunization. While 80% (95%CI 78.5, 81.9) of individuals believed that they received all of the vaccines required for someone their age, only 6% (95%CI 5.3, 7.4) had the recommended number of pertussis and tetanus vaccine doses in adulthood.

Discussion

In 2014, immunization coverage among Canadian adults was low in comparison to the national targets, none of which were met Footnote 12. Seasonal influenza vaccine coverage for older adults, persons with chronic medical conditions, and healthcare workers were similar to results reported in the United States Footnote 13 but estimates were below the 80% national target Footnote 12. Pneumococcal vaccine coverage among older adults was also well below the 80% goal Footnote 12.

More effort is required to increase vaccine uptake among Canadian adults, particularly among the recommended target groups. For uptake to increase, we need to improve our understanding of the factors affecting vaccination, to evaluate and identify effective strategies that drive uptake as well as to improve our methods to estimate immunization coverage.  Multiple factors have been identified that contribute to non-immunization including vaccine accessibility, knowledge and awareness, and recommendation from healthcare provider Footnote 14

In the general adult population, immunization coverage against pertussis was the lowest among all vaccines with publicly-funded programs. As identified by another study, there is low awareness of the Tdap vaccine among Canadian adults Footnote 15. Vaccination against pertussis may be underestimated by individuals who are unaware that the antigen is given as part of a combination vaccine. 

Immunization coverage for target groups at high-risk for severe complications were also suboptimal. Adults aged 65 years and older reported higher coverage for the seasonal influenza and pneumococcal vaccines as compared to individuals with chronic medical conditions, but estimates remain below the national targets. Individuals unaware that they are considered as a high-risk group may contribute to non-vaccination Footnote 16

While immunization coverage was higher among healthcare personnel as compared to the general adult population, many remained unvaccinated for publicly-funded vaccines such as influenza, pertussis and tetanus. In this target group, vaccination against hepatitis B was reported most frequently.

There are limitations to the 2014 aNICS study. The low response rate increases the risk of non-response bias (i.e. vaccine uptake may be different in those who did not participate) and limits the representativeness of the sample. Additionally, results are based solely on self-reported immunization history. The ability of the participant to recall specific vaccinations is influenced by their existing knowledge of vaccines and their understanding of the risks associated with the vaccine preventable-diseases. The self-reported results are likely to impact the accuracy and reliability of the estimates, resulting in under- or over-estimation of immunization coverage. As well, self-reported chronic medical conditions were not validated with medical records, which may have resulted in misclassification of individuals in high-risk groups. The aNICS results may not be directly comparable to coverage data reported by other countries because of differences in definitions of high-risk groups and measurement of vaccination coverage.

Conclusion

Immunization coverage estimates varied across target groups. There is room for improvement, as many Canadians are not up-to-date in their immunizations according to NACI-recommended schedules.

Promotion of and education about immunization to the general adult population requires greater effort to encourage uptake, particularly in individuals who are at higher risk of complications. Previously identified as a determinant of vaccine uptake, healthcare providers may play a strong role in raising awareness of vaccines given in adulthood to their patients. As well, it is important for healthcare personnel to be vaccinated because they are at risk of exposure to diseases from their patients and, for transmitting the disease to co-workers or other patients Footnote 17.

The aNICS constitutes an ongoing approach to measuring adult immunization coverage in Canada and monitoring progress towards national targets. The next aNICS cycle will take place in 2016. The Public Health Agency of Canada will continue to work to collaborate with provinces, territories and other stakeholders to improve immunization coverage assessment methodology. Public and professional education and outreach campaigns will also continue to promote the benefits and safety of immunization in Canada.

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