Pertussis, caused by Bordetella pertussis, is an acute, highly infectious disease. Despite high vaccination rates among children, an increase in the incidence of pertussis has been reported in recent years in some countries [1-4]. Pertussis remains a serious potential health risk to infants. Most deaths occur in the first 6 months of life, in those too young to be vaccinated or those who did not a complete vaccination schedule [5]. Adolescents and adults who come in close contact with young infants are the primary source of infection to susceptible and unprotected infants [6]. The primary goal of Tdap vaccination is to protect infants from severe disease. Vaccination of pregnant women and those in close contact with infants is recommended to protect very young infants. The latest Advisory Committee on Immunization Practice (ACIP) recommendation is to administer the Tdap to all unvaccinated pregnant women and adolescents and adults who come in close contact with infants aged < 12 months [7]. In Korea, the Tdap vaccination is not currently recommended during pregnancy; persons aged 11-64 years and postpartum women who have frequent contact with infants aged < 1 year are the main target groups for Tdap vaccination [8]. The recent estimated vaccination coverage of DTaP in a timely manner (at least 4 times) among Korean children ranged between 65.7% and 94.0%, but there is no such concrete data on the Td or Tdap coverage for adults [9] as well as women of childbearing age. Therefore, we studied the Tdap coverage rate and factors influencing the personal decision to receive Tdap among women of childbearing age in Korea.

Of the women of childbearing age, those who had previously received Tdap accounted for only 0.08% (n = 4) of all responders in this study, in spite of the recent substantial rise in the cases of pertussis reported in Korea.

The majority of pertussis cases, hospitalizations, and deaths occur in infants aged ≤ 2 months of age, who are too young to be vaccinated [7]. In Korea, the most common age groups affected by pertussis during 2010-2011 were those aged < 3 months and ≥ 15 years; intrafamilial transmission was common among these groups [9]. Considering that infants aged < 3 months usually stay at home and have no interaction with others besides their immediate family members, conducting a sensitive and timely examination of the asymptomatic or atypical symptomatic family members should be a public health priority [14]. Pertussis vaccination is the most effective strategy to reduce morbidity and mortality due to pertussis [15]. Therefore, the cocooning strategy, which involves immunizing all household and key persons in close contact with the newborns, with the Tdap, is suggested [16]. Usually, mothers are the key persons in contact with newborns, and therefore, Tdap vaccination for all women of childbearing age is very important for reducing morbidity and mortality due to pertussis among infants aged < 3 months.

In infants, maternal vaccination can prevent infections acquired during delivery through the placenta, until immunity is induced by active immunization. The Tdap should be administered to all pregnant woman on the basis of an assessment of its benefits versus its risks [17-19]. Several studies on the direct protection of infants by neonatal monovalent acellular pertussis vaccination reported that the vaccination could significantly increase the level of immunoglobulin G (IgG) antibody against pertussis antigen, but it also could result in interference in the development of immunity against hepatitis B and Haemophilus influenza type B [20-22]. Therefore, the current ACIP recommendation is to administer the Tdap to unvaccinated pregnant women in the third or late second (after 20 weeks gestation) trimester [7]. In Korea, there isn't any pertussis outbreak in these days. It is recommended that previously unvaccinated women of childbearing age receive the Tdap before pregnancy and postpartum Tdap vaccination is recommended for previously unvaccinated pregnant women. In the case of a pertussis outbreak, it is recommended that unvaccinated pregnant women receive the Tdap. Additionally, Tdap vaccination is recommended for all adults who are in frequent contact with infants aged < 1 year and family members who have neonates [8].

Despite the very low Tdap vaccination rate (0.04%) among women of childbearing age, all women who had received the vaccine had been advised to receive it by their healthcare provider, and 2 women (50.0%) were advised by their obstetrician or gynecologist. A recommendation from the healthcare provider was the leading factor influencing women of childbearing age to receive the Tdap vaccination. However, only 20 of the 500 women of childbearing age who visited the Department of Obstetrics and Gynecology received a recommendation for Tdap vaccination from their obstetrician or gynecologist. Education and a recommendation from an obstetrician or gynecologist about Tdap vaccination for women of childbearing age are necessary before and after pregnancy. The most common and important reason for not receiving the Tdap was the lack of information about the Tdap. Thus, it is important for the obstetrician or gynecologist to provide information about the necessity of receiving a Tdap and to recommend it actively.

One hundred seventy-one (34.2%) women replied that they would receive the Tdap in the future. The perception on risk of pertussis infection (n = 75, 43.9%) and a recommendation from a healthcare provider (n = 64, 37.4%) were the most common factors for receipt of the Tdap. In contrast, 329 (65.8%) respondents answered that they did not plan to receive the vaccination in the future, because they were unaware of pertussis and the Tdap vaccination (n = 276; 55.8%). The majority of women did not know that pertussis was a vaccine-preventable disease, although they knew that it was an infectious disease. It is possible that women might not feel the need to be vaccinated because they do not recognize the risk of pertussis infection. In fact, in the multivariate analysis of factors associated with Tdap vaccination plans, the statistically significant factors were general reliance on knowledge about vaccine effectiveness (OR: 1.80, 95% CI: 1.20 to 2.72) and awareness of the necessity of Tdap adults (OR: 3.36, 95% CI: 1.94 to 5.08). Concern about the adverse reaction of the vaccine was not an important factor for the decision of receiving the Tdap. Therefore, as a factor affecting the decision to receive the Tdap, gaining knowledge about the Tdap was more significant than having very little knowledge about pertussis.

The results of this study suggest that the major obstacles to increase the rate of Tdap vaccination among women of childbearing age are both unawareness about pertussis and Tdap and the lack of recommendation from a healthcare provider. Of the 500 respondents, 171 (34.4%) women decided to receive the Tdap. A recent study conducted to assess the decision-making process of women who accepted or declined receiving postpartum pertussis vaccination revealed 53% acceptance of vaccination among Taiwanese women [23]. To improve the Tdap vaccination rate among women of childbearing age, it is important that healthcare providers, including obstetricians and gynecologists, thoroughly brief women of childbearing age about the disease burden of pertussis for infants and actively recommend the Tdap.

This study had several limitations. First, the participants did not represent the entire population of women of childbearing age, as only those who visited the university hospital were recruited. Second, vaccination histories could be inaccurate because they were based on self-reporting without any confirmation from medical records.

In conclusion, the rate of Tdap vaccination among women of childbearing age is very low in Korea. To improve this vaccination rate, a recommendation from a healthcare provider and education of pertussis and the Tdap are important.