Hepatitis A (HA) affects health of infants and adolescents in underdeveloped and developing countries and affects the health of adults in more economically developed countries. It is a highly contagious disease transmitted through water or food contaminated by the stools of carriers [1,2]. HA rarely has complications, never becomes chronic, and its prognosis is relatively good. However, recently, some atypical clinical aspects have emerged, such as persistent hepatitis and recurrent hepatitis, and in some severe cases, death has occurred due to fulminating liver failure [3].

The HA antibody prevalence rate varies according to the economic level and hygiene of a particular country. In the United States, the HA seroprevalence rate was 31.3% overall, 9.4% for ages 6~11, and 74.6% over the age of 70 [4]. Similarly, the HA seroprevalence rate in Korea is low among children and young adults, but high among adults over 40 [5]. In South Korea in the 1980s, more than 90% of adults were immune to HA through natural infection [6]. However, the most recently reported seropositivity rate among people between 15 and 29 was between 11.7% and 13.0%[7]. In Korea, with improvements in economic prosperity and hygiene, fewer people have acquired natural immunity [8]. Cases of HA contracted overseas have also increased, as overseas travel to HA-endemic areas has become more common [8]. Accordingly, the risk of acute HA has become higher in children and young adults. Since 2008, the number of HA cases has increased rapidly, earning it the designation of a notifiable disease in 2011 [1].

Vaccination and practicing enhanced hygiene are steps recommended to prevent HA [1]. However, HA vaccination was not included in the mandatory vaccination list in Korea as of 2015, making vaccination against HA a personal choice. Oh and Park [9], in their study of university students, reported that age was a factor that influenced HA vaccination. Choi et al. [10] reported that decisions to vaccinate were made by parents, particularly by mothers, and Bardenheier et al. [11] reported that insufficient parental awareness of HA vaccination affected the vaccination rate.

Ajzen [12], who examined the factors that decisively influence human behaviors, considered "intention for behavior" to be an important variable in predicting behaviors. The theory of planned behavior (TPB) consists of 4 key concepts: attitude toward the behavior, subjective norm, perceived behavioral control, and intention. TPB has been used in the fields of sociopsychology [13,14] and healthcare to identify predictors and influencing factors [15,16]. Through a meta-analysis, Armitage and Conner [17] suggested that TPB is effective in predicting intention and behaviors. Researchers can also use TPB to explain vaccination intentions. TPB has been mainly applied to studies explaining and predicting cervical-cancer prevention behaviors related to the human papilloma virus vaccine [18-20]. Because the incidence of HA in Korea is relatively high among members of younger generations, active efforts are needed to improve the vaccination rate. Therefore, understanding the attitude toward the behavior, subjective norm, and perceived behavioral control as factors that influence mothers' intention to have their children receive HA vaccination may contribute to an increase in vaccination rates. In Korea, several studies [21,22] were conducted on factors related to HA vaccination in university students. A study on knowledge and health beliefs regarding HA vaccination [23] was conducted among parents. However, few studies have directly described the application of TPB for HA vaccination. Accordingly, this study aimed to contribute to the development of efficient nursing interventions designed to increase the HA vaccination rate and to prevent infection by using TPB to analyze factors influencing the HA vaccination intention of mothers with children under 19.

When a large population is vulnerable to HA infection, as in Korea, a sudden epidemic can be caused by something as simple as contaminated food. The most cost-effective strategy for reducing HA infection in a short time is to increase herd immunity through vaccination [24]. In Korea, HA vaccination started in 1997, and complimentary vaccination has been provided to children under 12 years of age since May 2015 [21,25]. However, those over 12 years old pay approximately 160,000 won (approximately US$140) for the 2-step vaccination process in Korea [26]. Therefore, youths between 13 and 19 who depend on their parents financially cannot make their own choices about HA vaccination. Because young people's attitude toward vaccination are influenced by their mothers' attitude [24], it is meaningful that this study investigated mothers' attitudes and health beliefs regarding vaccination.

In the present study, mothers' attitudes toward HA vaccination were relatively positive. Participants also reported relatively high scores for perceived behavioral control, subjective norm, and vaccination intention. In other words, Korean mothers' attitudes toward HA vaccination were relatively positive. In addition, they felt that vaccination was straightforward to accomplish, and the social pressure for HA vaccination was relatively high. Yoon et al. [24] reported that the HA vaccination rate for parents was 2.5%, and that for their youth was 0.6%. However, in the present study, the HA vaccination rate for mothers was 35%, and their children's rate was 59%. These results show that parents who were vaccinated against HA had a more positive attitude and higher HA vaccination-intention scores. The HA vaccination rate for children in the present study was similar to the result reported in the study conducted by Yoon et al. [8] of participants under the age of 10 living in central Korea, but it was higher than the rate of 42.2% of kindergarten children in the United States reported by Bardenheier et al. [11]. Although studies have shown that low socioeconomic status was related to a low vaccination rate, Bardenheier et al. [11] reported that mothers who had 12 or fewer years of education and had an annual income under US$50,000 demonstrated a higher likelihood of having received an HA vaccination. However, no significant difference emerged according to income in the present study. In addition, no difference in attitude toward HA vaccination, perceived behavioral control, subjective norm, and vaccination intention emerged between mothers who had graduated from high school and those with university degrees.

In the present study, many participants planned to vaccinate their children against HA. However, the actual HA vaccination rate was 59%, which is somewhat lower than the rate for intention. Yoon et al. [24] found that the main reason participants reported not receiving vaccination against HA was that they were unaware of the need for HA vaccination or its vaccination schedule. Bardenheier et al. [11] reported that influencing factors against HA vaccination included the lack of a doctor's or health department's recommendation and the lack of parental awareness. Therefore, this suggests that vaccination education, including the vaccination schedule, is essential for increasing HA vaccination rates.

In the study of Bardenheier et al. [11], a significant difference in attitude towards HA vaccination depending on awareness of HA was found, but no significant difference emerged in the present study. In Korea, vaccination against HA was not mandatory until April 2015. Vaccination of children under 19 was therefore performed when parents chose that option. Thus, parents' perceptions and attitudes had an effect on children's vaccination [24]. In the present study, participants had a relatively high education level, so they seemed to be aware of the necessity of HA vaccination.

In the present study, the strongest influencing factor of intention to give children the HA vaccination was mothers' attitude toward HA vaccination, followed by subjective norm. The study results suggest that higher vaccination intention is present when mothers have a positive attitude toward HA vaccination and when they experience increased pressure to vaccinate from others. Kim and Choi [27], who conducted research on mothers' intention of HPV vaccination based on the TPB, also showed a similar result to that of the current study: mothers' attitude and subjective norms were significant predictors for intention of HPV vaccination. Park [28] reported that the more positive attitude on preventive health behavior of hepatitis, the higher the compliance with preventive behaviors. This result is similar to the results of the present study. In addition, Park [28] stated that it is likely for Koreans to be infected by HA over time, because Korean culture includes passing glasses around or sharing food in a bowl, providing many opportunities for infection in group situations such as military service and overseas travel, which increases every year. The Korea Centers for Disease Control and Prevention [1] stated that prevention is most crucial for HA, suggesting vaccination, hand washing, boiling water, eating cooked food, and hygienic cooking as prevention methods. Therefore, it is necessary to promote the effectiveness and benefits of HA vaccination, to provide free infant immunization, to promote personal hygiene.

This study was limited in that it only included participants from Seoul and Gyeonggi Province in Korea. Therefore, it would be difficult to generalize the study results to all mothers with children and adolescents. Follow-up studies on HA vaccination knowledge, intention, and health beliefs of mothers from various backgrounds are therefore proposed.

This study showed that the attitude of mothers with children under 19 toward HA vaccination was very positive, and their scores for perceived behavioral control, subjective norm, and vaccination intention were relatively high. Attitude toward HA vaccination was the strongest influencing factor, followed by subjective norm. Therefore, providing information on the importance of HA vaccination and the vaccination schedule would help develop positive attitude toward vaccination. In addition, efforts to enhance the subjective norm of HA vaccination are also needed to improve perceptions of the importance of HA vaccination. These efforts should include public service announcements and educational programs offered at the institutional (schools and medical establishments) and governmental levels.