Influenza vaccine uptake: Results from the 2015-16 National Influenza Immunization Coverage Survey in Canada

From Public Health Agency of Canada

This report summarizes the results of the 2015-16 National Influenza Immunization Coverage Survey. Between February and March 2016, information on uptake of the influenza vaccine, also known as the flu shot, was collected from 2000 adults through telephone interviews.

Key findings

• Canada’s national immunization coverage goal of 80% remains unmet among population groups considered at high risk for influenza-related complications including those with at least one chronic medical condition (CMC),  seniors aged 65 and over, and children aged six months to four years of age.
• Results of the survey indicate that influenza immunization coverage was moderately high at 65% in Canadian seniors aged 65 years and older.  However, immunization coverage was 37% in adults aged 18 – 64 years with at least one CMC and 31% in children aged six months to four years, which is low compared to the national goal of 80%.
• Doctor’s offices and pharmacies were the most commonly reported places for immunization among adults, with most getting their immunization at the beginning of the flu season in October and November 2015.
• Among adults aged 18 years and over, the most frequent reason cited for getting immunized against influenza was to avoid transmitting the disease to others (17%).

Introduction

Influenza (the flu) usually occurs in the northern hemisphere between November and April. In Canada, an average of 12,200 hospitalizations and 3,500 deaths related to the flu occur each year^{Footnote 1}. The risk of hospitalization is greatest in very young children and elderly persons.

The best way to prevent the flu is by getting an influenza vaccine, also known as a flu shot.  It is important to get a new flu vaccine every year for two reasons.  First, the effectiveness of the vaccine can wear off, it is therefore important to get immunized every year to stay protected.  Second, the type of flu virus in circulation usually changes from year to year and experts create a new vaccine based on the virus in circulation every flu season.

Provinces and Territories (PT) usually launch their influenza immunization programs in October, and the best time to get the influenza vaccine is between October and December, before the influenza begins spreading in the community. However, vaccination continues to be offered throughout the flu season, even in January or later, as long as influenza viruses are circulating.

The National Advisory Committee on Immunization (NACI) recommends that all individuals six months and older receive the annual seasonal influenza vaccine, especially for populations at high risk for influenza-related complications (e.g. those with chronic medical conditions, older adults, and children aged six months to 59 months) ^{Footnote 2}.

Based on the 2005 National Consensus Conference on Vaccine-Preventable Diseases in Canada, national immunization coverage goals for influenza are 80% for adults aged 65 and older and 80% for persons less than 65 years of age with high-risk conditions)^{Footnote 3}. Internationally, the World Health Organization (WHO) has set a coverage goal of 75% among elderly people^{Footnote 4}.

Measuring influenza immunization coverage every year is important to evaluate immunization programs, to identify sub-populations with low immunization coverage and to monitor progress towards Canada’s national immunization coverage goals. Collecting this information helps to inform influenza immunization program planning for subsequent seasons.

This report describes 2015/16 seasonal influenza immunization coverage for the general adult population, children and, specific target groups.

Survey methods

The 2015/16 National Influenza Immunization Coverage Survey was conducted between February and March 2016 by Léger. Respondents from every Province and Territory were selected using random digit dialing which included land lines and known cellphone-only household numbers. Sampling was stratified by Province and Territory. All estimates from the survey were weighted to represent the Canadian population based on age, gender and Province/Territory using data from the 2011 Canadian Census.

Data were collected using computer-assisted telephone interviewing. A total of 2000 adults were interviewed on questions regarding their influenza vaccine uptake for the 2015/16 season, reasons for receiving or declining the vaccine, and demographic information. Respondents who were parents of children living in the same household were asked additional questions on influenza vaccine uptake for their children.

Influenza immunization coverage was estimated 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). Simple weighted proportions were calculated for place, month of, and reason for immunization among immunized adults only.  For immunization coverage estimates in children, the analysis adjusted for the fact that children in the same household are more likely to have the same immunization status as each other.

Influenza vaccine coverage among adults

(Table 1) shows that, among Canadians aged 18 years and older (n=2000), 34% reported receiving the 2015/16 influenza vaccine. The immunization coverage was 65% in adults aged 65 years or older, and 37% in adults aged 18 to 64 years with a CMC; they were therefore below the national goal of 80% coverage set for these target groups (Table 1).

In the 2012/13 influenza season, based on a survey of 2008 Canadian adults, the coverage rate in adults aged 65 years or older was 62%.  In adults aged 18 to 64 years with a CMC, the coverage rate was 33% while in adults aged 18 to 64 years without a CMC the coverage rate was 19%.

When comparing results of the 2012/13 and the 2015/16 surveys, there appears to be an improvement in the uptake of the vaccine in adults aged 18 to 64 years without a CMC from 19% to 24%. However, the differences in coverage rates observed between the two surveys among seniors over the age of 65 and in adults with CMC are within the margin of error of the survey.

This means that we cannot conclude to an increase in influenza uptake among adults aged 65 years or older nor can we conclude to a decrease in coverage rate for adults aged 18 to 64 years with a CMC.

Similar results were seen in past years of the Canadian Community Health Survey (CCHS), where immunization coverage estimates were 63-64% among seniors aged 65 and over between 2009-2010 and 2013-2014 (calendar years). Overall influenza immunization coverage estimates among 12 years and older were 29%, 30% and 31% in 2009-2010, 2011-2012 and 2013-2014, respectively^{Footnote 5} .

Table 1. Influenza immunization coverage among adults by age group and medical conditions, National Influenza Immunization Coverage Survey, Canada, 2015 /16

Age Group (years)	n	Influenza Immunization Coverage (95% confidence interval)
All adults (≥ 18)	2000	34.3 (31.9, 36.7)
18 – 49	801	22.4 (19.0, 25.7)
50 – 64	647	37.9 (33.8, 42.0)
≥ 65	514	64.6 (60.2, 68.9)
18 – 64	1448	27.9 (22.2, 30.5)
18 – 64 with chronic medical conditionFootnote *	408	37.2 (31.9, 42.5)
18 – 64 without chronic medical condition	1028	24.4 (21.4, 27.4)
n = number of respondents (non-weighted) table note * 12 respondents had missing information or refused responses to chronic medical conditions. Chronic medical conditions associated with influenza-related complications as defined by NACI included: asthma, chronic lung disease, heart condition, cancer, diabetes or other metabolic diseases, chronic liver disease, chronic kidney disease, immune disorder/suppression, spleen problems/removal, anemia/thalassemia, morbid obesity, and conditions that compromise management of respiratory secretions. Return to table note * referrer

Coverage in Canadian seniors was similar to what was measured in the United States (US). However, for adults with CMC, coverage in Canada was lower. In the US, during the same influenza season (2015/16), those aged 65 years and older had immunization coverage of 63%, while those 18-64 years of age with a high-risk condition had immunization coverage of 46% ^{Footnote 6}.

Month and place of immunization among vaccinated adults

Among adults that received their 2015/16 seasonal influenza vaccine (n=774), 82% were immunized in October and November 2015 (Table 2).  This reflects the messaging and timing of PT immunization campaigns encouraging Canadians to get the influenza vaccine early during the influenza season before flu begins spreading in the community.

Doctor’s office and pharmacies were the most commonly reported places of immunization (Table 3). In 2015, nine out of 13 provinces and territories allowed pharmacists to administer influenza vaccines. In these jurisdictions, the uptake of the vaccine in the population increased when pharmacists were authorized to vaccinate^{Footnote 7}.

Table 2. Month of influenza immunization among immunized adults aged ≥ 18 years (n=774), National Influenza Immunization Coverage Survey, Canada, 2015/16

Monthtable 2 note *	Proportion Immunized in this Month (95% confidence interval)
October 2015	40.6 (36.6, 44.6)
November 2015	41.0 (37.1, 45.0)
December 2015	9.0 (6.6, 11.5)
January 2016	3.3 (1.5, 5.1)
February 2016	0.3 (0.0, 0.7)
note * 42 respondents did not know month of immunization Return to table note * referrer

Table 3. Place of immunization among immunized adults aged ≥ 18 years (n=774), National Influenza Immunization Coverage Survey, Canada, 2015/16

Place of immunization	Proportion Immunized by Location (95% confidence interval)
Doctor's office	33.1 (29.3, 36.9)
Pharmacy	29.6 (25.9, 33.4)
Temporary vaccine clinic	12.2 (9.4, 15.0)
Community health centre	8.0 (6.0, 10.0)
Workplace	7.7 (5.5, 10.0)
Hospital	6.2 (4.2, 8.2)
Other	2.8 (1.4, 4.2)
*4 respondents did not know place of immunization

Reasons for vaccination among adults

Among adults that received their 2015/16 seasonal influenza vaccine (n=774), 99% (n=769) of respondents provided at least one reason for being immunized.

Table 4 provides information on the reason given by respondents for getting the flu shot.  Avoiding the transmission of the disease to others was the most frequent reason given by adults aged 18 years and older (17%), as well as by adults 18-64 years without chronic medical conditions (26%). 

The most frequent reason for getting the flu shot among adults 18-64 with chronic medical conditions was to prevent infection (35%), whereas for adults aged 65 years or older, it was that they received the vaccine on a yearly basis (20%).

Table 4. Top three most frequent reasons for immunization among immunized adults aged ≥ 18 years, National Influenza Immunization Coverage Survey, Canada, 2015/16

	Reason:	%	(95% CI)
All adults (≥18) (n=769)	If not immunized, can transmit disease to others	17.1%	(13.7-20.5)
	To prevent infection/don't want to get sick	14.5%	(11.8-17.2)
	Receive vaccine yearly	11.4%	(9.0-13.7)
18-64 without CMC (n=269)	If not immunized, can transmit disease to others	26.3%	(20.2-32.5)
	Required by workplace	16.0%	(11.2-20.8)
	Recommended by health care professional	10.9%	(5.9-15.9)
18-64 with CMC (n=156)	To prevent infection/don't want to get sick	34.6%	(26.4-42.9)
	If not immunized, can transmit disease to others	16.4%	(8.6-24.2)
	Recommended by health care professional	10.0%	(5.2-14.8)
≥65 (n=330)	Receive immunization yearly	20.4%	(15.9-25.0)
	At risk because of age	16.2%	(12.0-20.4)
	To prevent infection/don't want to get sick	13.8%	(9.9-17.7)
Note: Respondents could provide more than one reason for immunization CMC – Chronic medical condition(s) CI – Confidence interval

NACI recommends that all children aged six months and older receive the seasonal influenza vaccine, especially those six months to 59 months of age, who are at higher risk for influenza-related complications^{Footnote 2}.  Children six months to less than nine years of age who are receiving the flu shot for the very first time require two doses of the influenza vaccine with a minimum interval of four weeks between doses^{Footnote 2}.

Among children living in the same household as the adult respondent (n=645), 22% received the 2015/16 seasonal influenza vaccine (Table 5).  Children six months to four years of age had the highest coverage as compared to children in older age groups.  Of the 26 children getting the flu vaccine for the first time and requiring two doses, 11 had received their two doses by the time of the interview.

Table 5.  Influenza immunization coverage among children (<18 years) by age group, National Influenza Immunization Coverage Survey, Canada, 2015/16

Age Group	n	Influenza Immunization Coverage (95% confidence interval)
All children (6 months – 17 years)	645	21.7 (16.7, 26.6)
6 – months – 4 years	160	30.9 (21.4, 40.4)
5 – 12 years	296	21.5 (14.5, 28.5)
13 – 17 years	189	16.1 (9.1, 23.0)
n = number of respondents (non-weighted)

Survey limitations

The survey had a low response rate of 20%, which 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.  Coverage estimates are based on self-reported immunization history and may result in under- or over-estimation of uptake.  Survey sampling was designed for estimating adult immunization coverage only, and, as such, results for children may not be nationally representative because sampling was designed to assess coverage in adults.

Conclusions

Despite the fact that the flu vaccine is the best protection against the flu, influenza immunization coverage rates in Canada for the 2015/16 flu season remain below national goals of 80% among population groups considered at high risk of complications from the flu.  Coverage also remains below the WHO goal of 75% among elderly people with a coverage rate of 65% among seniors aged 65 years and older.  Coverage was 37% among adults aged 18 to 64 years with a CMC, far below the national goal of 80%.

There has been no change of the vaccine uptake in these two high-risk populations compared to a similar survey conducted in the 2012/13 flu season. In contrast, coverage increased in adults aged 18 to 64 years without CMC.

References