Low Coverage of Influenza Vaccination among Chinese Children Aged 12-23 Months: Prevalence and Associated Factors

The very few studies of annual influenza vaccination (IV) conducted among children under 2 years old have found that health care workers' recommendation, parental concerns about side effects, and parental positive attitudes toward IV are significant factors in the decision. In light of the knowledge gap about factors of IV for children under 2, this study investigated prevalence and associated factors of IV among children aged 12-23 months in Hong Kong. Besides socio-demographics, potential factors that were studied include: 1) family members' IV status, 2) parental perceptions of the Health Belief Model (HBM) and subjective norm of the Theory of Planned Behaviors (TPB), 3) parental fear experienced during the H1N1 pandemic (H1N1 has become a major source of seasonal influenza), and 4) exposure to related mass media messages.

As the researchers explain, behavioural health theories are commonly used to understand factors of IV. The HBM examines parental perceived susceptibility to and perceived severity of influenza, perceived IV benefit, perceived IV barriers, cues to action, and self-efficacy related to IV as determinants of young children's IV. Given its wide applicability, the present study used it as the theoretical framework. In addition, subjective norm, defined as perceived support from significant others for performing a health-related behaviour, a construct of the TPB, was relevant, as family members and friends influence parental decision on children's IV. A local (Hong Kong) study found that factors of IV for 24- to 59-month-old children included family members' IV experience, subjective norms and those related to the HBM, family members' IV experience, and exposure to influenza-related media messages. Fear experienced during the H1N1 pandemic was also potentially important, as fear induced from SARS/H1N1 was associated with intention to take up IV. Thus, the present study considered such factors.

The cross-sectional survey interviewed 489 parents of children aged 12-23 months anonymously at 12 maternal and child health centres in Hong Kong. Results showed that only 11.5% of the children had ever received IV (64.3% being subsidised). Of the participants, 7.5% and 45.2% perceived high susceptibility for their child to contract H1N1 and seasonal influenza, respectively, and 28.4% and 19.1% perceived high severity of H1N1 and seasonal influenza, respectively. Over half (57.1% to 68.1%) perceived some benefits of IV; 43.1% believed that the currently available influenza vaccines were more effective than the previously available ones. Concerning perceived barriers, prevalence of items reflecting safety concerns ranged from 35.0% ("This vaccine is not safer than the previous one") to 58.5% ("My child is too young to take up IV"); concern for barriers of cost and inconvenience was less common (23.7% and 16.4%). Regarding cues to action, only 12.9%-19.2% had received advice concerning the child's IV from healthcare providers, peers/other parents, and relatives/friends; 17.2% believed that it was common for children of similar age to take up IV; and 48.3% believed in the governmental recommendation on IV for young children. Perceived self-efficacy was very high (90.6% and 92.8%). Regarding subjective norms, less than half found that their spouse (42.9%) and other family members (40.7%) were supportive of the child's IV. About half (47.9%) had experienced moderate to severe levels of fear during the H1N1 pandemic. In the last 3 months, 27.4% had often/frequently been exposed to media messages depicting severe complications and/or deaths caused by influenza among children; 54.8% had often/frequently been exposed to media messages promoting IV.

Adjusted for the child's age, significant factors of the children's IV included parental knowledge about governmental policy/recommendation (adjusted odds ratio (AOR) = 2.64, 95% confidence interval (CI) = 1.09, 6.40), knowledge about annual IV requirement (AOR = 2.30, 95% CI = 1.21, 4.38), perceived safety-related barriers (AOR =0.14, 95% CI = 0.06,0.33), cue to action (AOR = 7.79, 95% CI = 3.45, 17.58), and subjective norm (AOR = 4.59, 95% CI = 2.34,9.00). IV prevalence of children aged 12-23 months remained low despite a subsidisation scheme. However, an important insight comes from the very strong positive association between the child's age and IV uptake observed in this study. It seems that many parents did not object to IV for their children, but instead, postponed their action, as 58.9% of the children aged 24-59 months had taken up IV in 2011 (during approximately the same study period as this one) versus 11.5% of the 12- to 23-month-old children involved in this study. Also, 58.5% of the parents perceived that their children were too young to take up IV. According to the researchers, young children's parents need to know that side-effect of IV among young children is not age dependent and that children aged 12-23 months need as much protection as older children, and as early as possible.

This study and other studies consistently found strong associations between health care workers' advice and the child's IV status. The adjusted analysis of both this and the independent concurrently conducted survey in a 24- to 59-month-old group found very strong associations between cue to action (including that given by health professionals) and IV status. About 20% of the participants had been advised about their children's IV, which was almost doubled when compared to the data (10.6%) obtained from a comparable survey conducted in 2006. The prevalence of this study was still low, despite improvement. Thus, the researchers assert, health care workers need to play a stronger role in information dissemination and promotion of IV for children under 2 years old. The government should also promote the knowledge that IV is required annually for young children, which was another significant factor of IV in this study.

In this study, about 40% of the indexed children had been infected by influenza, but the experience was not associated with IV status. This implies that prior experience of influenza cannot motivate parents to vaccinate their children. On the other hand, both family members' IV experience and supportive subjective norms (of spouse and family members) were significant in both the adjusted and stepwise analyses. Although IV among young children is a family matter, only half of the spouse and family members were supportive of the child's IV both in this and the 24- to 59-month-old group studies. According to researchers, as a new approach, counseling is needed to harmonise divergent opinions about children's IV and to enhance communication skills among parents. "We should hence engage parents' social networks, possibly through social media or other means."

Only 2 HBM constructs (perceived barriers and cue to action) were found to be significant factors. Making IV more convenient and less costly might not be effective in promoting IV, as perceived efficacy and cost as perceived barriers were not significant factors in this study's age group. Related media exposure was non-significant, suggesting that general media campaigns are not promising. Fear experienced during the H1N1 pandemic was not a significant factor for this study's age group. The observation that most of the local health promotion campaigns for IV among young children have been engaging some of the aforementioned non-significant components might partially explain the low IV prevalence in this age group.

To conclude, prevalence of IV among 12- to 23-month-old Chinese children in Hong Kong was low and showed little improvement as compared to 2006. The researchers suggest that the government revamp related health promotion strategies and treat the young age group (12-23 months) as a distinct segment. They indicate that promotion campaigns should shift emphases from cost reduction and mass media approaches to dissemination of knowledge about IV policy and safety, enhancement of health professionals' advice, and creation of supportive subjective norms.