Universal immunization of infants has been an important tool in controlling infectious diseases in the past century. Timeliness of immunization is important in achieving a protective effect at the individual and population levels.1–3 Timely vaccinations provide protection to children as early as possible and prevent disease outbreaks. In addition, delay in receiving vaccinations has been shown to have negative implications for the receipt of other preventive healthcare services.4
The factors affecting timely initiation and completion of infant immunization remain unclear, despite several studies on the subject worldwide.5–8 Moreover, there are limited studies assessing the impact of a maternal intervention on the timeliness of infant immunization. One prospective randomized cohort study to assess the effectiveness of an educational intervention with pregnant Latinas failed to show significant impact; another randomized controlled trial showed a significant improvement in infant immunization completion rates after an educational intervention for mothers in Pakistan.9,10 Our study is the first study looking at the impact of both maternal immunization and vaccine education in the immediate postpartum period on the timeliness of infant immunization.
In 2006, Advisory Committee on Immunization Practices recommended routine administration of tetanus toxoid, reduced diptheria toxoid and acellular pertussis (Tdap) for postpartum women who were not vaccinated previously with Tdap as part of a cocooning strategy to provide personal protection to the mother and reduce the risk of her transmitting pertussis to her infant.11 In response to 2 infant deaths from pertussis in Philadelphia in 2007, the Philadelphia Department of Public Health started a Tdap vaccine initiative at 3 hospitals in the Philadelphia area to immunize postpartum mothers before hospital discharge. The intervention provided an opportunity to examine whether maternal immunization had an effect on timeliness of infant immunization in addition to its protective effect on the newborn.
MATERIALS AND METHODS
Study Design and Study Population
We performed a retrospective cohort study assessing the timeliness of immunization in infants born to mothers who had received postpartum Tdap vaccine after the introduction of routine maternal Tdap vaccine in May 2008 as compared with a historical cohort of infants born before the initiative. The Tdap vaccine intervention group consisted of all mothers discharged from the postpartum unit in July 2008 and their infants (n = 250). The pre-Tdap control group was comprised of all mother–infant dyads discharged from the same unit in July 2007 (n = 238). This study was carried out at Einstein Medical Center Philadelphia (EMCP), an academic hospital serving a minority, low income, urban community. The study was approved by the EMCP Institutional Review Board and the City of Philadelphia Department of Public Health Institutional Review Board.
The postpartum Tdap intervention was started in May 2008 and consisted of standing Tdap vaccine orders for all women in the immediate postpartum period. Immunization was provided in an opt out manner where women had to sign a refusal form if they did not want to receive the vaccine. Immunization administration was accompanied by education about pertussis and Tdap vaccine.
Maternal data were collected from the EMCP postpartum unit. The data for mothers in the intervention group were obtained from the Tdap vaccine initiative log for July 2008. This log contained names and medical record numbers and the acceptance or refusal of Tdap vaccine for all mothers discharged from the postpartum unit during July 2008. A similar discharge list (minus the Tdap vaccine receipt status) was used to obtain maternal data from July 2007. Further information about maternal age, ethnicity and insurance status was obtained from the electronic medical record at EMCP.
Infant immunization data were collected from the Philadelphia Department of Public Health citywide immunization registry called Kids Immunization Database System (KIDS) registry. All providers in the city of Philadelphia are required by law to report all immunizations given to children between ages 0–18 years to the KIDS registry.
Outcome measures were completeness of the first set of vaccinations by 3 months, and completion of the primary series by 8 months and by 9 months of age. Infants’ immunizations were tracked to the age of 9 months through the KIDS Registry.
Completion of the first set of immunizations was defined as receipt of the second dose of Hepatitis B and the first dose each of diphtheria and tetanus toxoids and acellular pertussis vaccine, Haemophilus influenzae type b conjugate vaccine, pneumococcal vaccine and inactivated poliovirus vaccine. Completion of the primary series of immunization was defined as receipt of 3 doses each of Hepatitis B, diphtheria and tetanus toxoids and acellular pertussis vaccine, Haemophilus influenzae type b conjugate vaccine, pneumococcal vaccine and inactivated poliovirus vaccine.
The difference between timeliness of immunizations was considered statistically significant if the P value was less than 0.05. Statistical analyses were performed using the Fisher’s exact probability test for categorical data and χ2 analysis for independent data.
The 2 groups were similar in ethnicity, percent Medicaid, mean maternal age and percent teenage mothers. The majority of patients were African-American with Medicaid insurance. The mean age for mothers was 26 years in the Tdap group and 25 years in the control group, with less than 20% teenage mothers in each group. Twelve of the 250 mothers discharged in the month of July 2008 refused the Tdap vaccine. Because this was a retrospective study, the reasons for refusal of vaccine were not available to the investigators. However, these mother–infant pairs were excluded from the study. Furthermore, 29 infants from the Tdap group and 35 from the control group were excluded because of absent or incomplete immunization records in KIDS Registry. These records were defined as incomplete if there was only documentation of the first Hepatitis B vaccine administered at birth. Hence, we were able to assess the timeliness of immunizations for 209 infants in the Tdap group and 203 in the control group.
The infants whose mothers received Tdap in the postpartum period were more likely to receive their first set of immunizations by 3 months of age (88% vs. 82%, P = 0.03) when compared with the control group. Infants in the Tdap group were also more likely to be up-to-date with the primary series by 8 months of age (67% vs. 57%, P = 0.008) and by 9 months (75% vs. 65%, P = 0.007) (Table 1).
Our data suggest that postpartum maternal Tdap vaccine intervention in our institution may have had a positive impact on timeliness infant immunization. The primary intent of this intervention was to cocoon unimmunized newborns by protecting the mother from getting pertussis. The improvement in the timeliness of infant immunization was a secondary benefit that might not have been anticipated.
Why did we find more timely immunization of infants whose mothers received the postpartum Tdap compared with those whose mothers did not? The Health Belief Model, first described in the 1950s, remains a helpful conceptual framework for understanding preventative health behaviors. According to this model, the likelihood of action is determined by perceptions of susceptibility, benefits minus barriers and self-efficacy.12,13
The process of consenting to postpartum Tdap vaccination and receiving education about the vaccine may have increased the mothers’ perceptions of the susceptibility of their infants to pertussis and the benefits of immunization. Several studies have shown that lack of information about vaccines is associated with suboptimal compliance to immunizations.14–16 Also, the mothers’ experience of getting the immunization may have removed some barriers to immunizing their infants by making them less fearful of vaccines. Concerns about vaccination safety have been shown to be associated with lower childhood immunization rates.17,18 Additionally, the postpartum Tdap vaccine intervention itself may have improved mothers’ perceptions of self-efficacy by making them feel empowered to do something to protect their child. Vaccination rates have been shown to be lower in cultures with insufficient empowerment of women.17 These speculations need further investigation.
It is strength of the study that it showed a statistically significant impact of a postpartum maternal Tdap intervention on timeliness of infant immunization in a low income minority population. However, it is unclear if this difference is clinically significant or generalizable to a different population. Additionally, although we compared maternal age, ethnicity and insurance status, other confounding factors such as maternal parity and social structure were not collected.
The design of the study may represent a limitation as historical controls were used. Although no major changes in the demographics of the patient population served between 2007 and 2008 was noted, public health efforts to increase awareness of the importance vaccination to prevent pertussis may have impacted the results of our study. Another possible limitation is our data source for immunization records. Infants who received their immunizations outside Philadelphia County were unable to be counted and could have swayed the data in either direction.
With the encouraging results seen in our study, a large prospective multicenter or geographic sampling study is indicated to further evaluate the impact of postpartum maternal vaccination efforts on childhood immunization. Moreover, the reasons for maternal refusal of postpartum Tdap vaccine were not available in the records reviewed and thus were not assessed in this study. This should prompt future investigators to include such information in the study design in order to enhance educational efforts directed at improving vaccination rates both nationally and globally. Achieving more complete primary series coverage continues to be necessary as documented by the increasingly large number of pertussis outbreaks19,20 and the persistence of other vaccine preventable diseases.
We thank Matilde Irigoyen, MD, and Allan M. Arbeter, MD, for helpful editorial comments.
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