Study Summary: Pneumococcal Vaccination Among Children With Sickle Cell Anemia, Sickle Cell Trait, and Normal Hemoglobin

Study Highlights

• Compared with children with normal hemoglobin, those with sickle cell anemia and sickle cell trait have a higher risk for invasive pneumococcal disease, which may lead to severe complications and death.
• Pneumococcal vaccination is an essential component of prevention of pneumococcal infections; however, rates of pneumococcal vaccination remain less than ideal, especially among those with low socioeconomic status.
• Emphasis should be given to strategies to increase pneumococcal vaccination coverage among children of low socioeconomic status with sickle cell anemia or sickle cell trait.

Background

Invasive pneumococcal disease (IPD) is a bacterial infection that causes substantial morbidity and mortality among children in the United States.¹ The Advisory Committee on Immunization Practices (ACIP) recommends that all children receive 4 doses of pneumococcal conjugate vaccine (PCV) at the ages of 2, 4, 6, and 12 to 15 months.¹ Although the rate of PCV vaccination coverage has risen to approximately 84% and the incidence of IPD in children younger than 5 years old has decreased, an estimated 3700 deaths from pneumococcal meningitis and bacteremia still occurred in 2013.¹ Vaccination coverage refers to the percentage of the population who received the pneumococcal vaccine.

Children with chronic conditions, including cancer, cardiovascular disease, organ transplantations, and asplenia, have a higher risk of IPD.¹ Asplenia is a common complication of sickle cell anemia (SCA), and the risk of IPD among children with SCA is more than 100 greater compared with children with normal hemoglobin. In addition to 4 doses of PCV, the ACIP and the National Heart, Lung, and Blood Institute (NHLBI) recommend that children with chronic diseases receive 2 doses of pneumococcal polysaccharide vaccine (PPSV) between the ages of 2 to 18 years.

Patients with sickle cell trait (SCT) are carriers (ie, they have 1 sickle cell gene and 1 normal gene) and are often asymptomatic. Although the risk of IPD among children with SCT is not as high compared with those with SCA, patients with SCT have a higher risk of IPD than children with normal hemoglobin. However, additional vaccination with PPSV is not recommended for patients with SCT. Through newborn screening (NBS), children with SCT may be identified at birth. As part of this study, investigators conducted an analysis of NBS records and immunization registry data to compare pneumococcal vaccination rates among children with SCA, SCT, and normal hemoglobin.¹

Study Design

This cohort study evaluated age-appropriate pneumococcal vaccination among children with SCA, SCT, and normal hemoglobin enrolled in Michigan Medicaid for at least 1 year.² Children with other forms of health insurance were excluded.¹ Eligible children with SCA and SCT were identified using statewide Michigan NBS records for all births from 1997 to 2014. A comparison group was generated by matching each child with SCA or SCT with 10 children with confirmed normal hemoglobin based on birth year, year(s) of enrollment in Michigan Medicaid, race, and residence; from this pool of 10 matched children, 4 comparison children were randomly selected for each child with SCA or SCT. Pneumococcal immunization status was determined based on data from the Michigan Care Improvement Registry.¹

The primary measure evaluated was age-appropriate pneumococcal vaccination per ACIP immunization guidelines.¹ Children were evaluated at the milestone ages of 3, 5, 7, and 16 months, allowing for a 1-month grace period after the ACIP recommended ages for dose administration. Children with SCA were also evaluated for compliance with the 2 doses of PPSV recommended by ACIP and NHLBI at the milestone ages of 5 and 10 years (plus 1 month for both milestones as a grace period).¹ Appropriateness was determined based upon whether the child received the recommended number of doses at each age milestone.¹

Results

From 1997 to 2014, a total of 592 children with SCA and 33,404 children with SCT were born in Michigan. This study included 355 children with SCA, 17,319 with SCT, and 70,757 with normal hemoglobin. The majority of the children in the study population were black (SCA = 77.8%, SCT = 81.3%, normal hemoglobin = 81.1%).¹

In general, the proportion of children with age-appropriate PCV vaccination coverage decreased with each successive age milestone, with a slight increase at the last milestone (16 months); rates were 69.4%, 49.5%, 34.8% and 38.3% at 3, 5, 7, and 16 months, respectively. PCV vaccination coverage was significantly greater in the SCA group at each milestone compared with both SCT and normal hemoglobin groups (P <.01 for all comparisons).¹ Children in the SCT group had a significantly higher rate of PCV vaccination coverage than the normal hemoglobin group at milestone ages 7 and 16 months (P values not reported); however, these differences were not clinically meaningful.¹

In the SCA group, rates of age-appropriate pneumococcal vaccination coverage (PCV and PPSV doses) at 5 and 10 years were 64.3% and 52.7%, respectively.¹

Discussion and Conclusion

Although the rate of age-appropriate pneumococcal vaccination coverage was higher in the SCA group (compared with the SCT and normal hemoglobin groups), the authors noted that there were opportunities for improvement in all groups. The rate of pneumococcal vaccination observed here was considerably lower than PCV completion rates of 66% to 84% reported by other researchers. Given the study population demographics, the lower rates of vaccination may be primarily attributable to racial disparities and lower socioeconomic status. The rate of vaccination seen here was reflective of a lower socioeconomic status as compared with the overall population of children in the United States.¹ On average, black children are less likely to receive the 4-dose PCV vaccination series compared with white children. Additionally, children with SCA tend to live in less affluent areas compared with children without SCA.

The authors recommend that programs to increase vaccination coverage in children with SCA or SCT and low socioeconomic status should be emphasized. Multicomponent interventions that include education are strongly recommended by the Task Force on Community Preventive Services and have been shown to increase vaccination rates in populations of lower socioeconomic status. With regard to children with SCA, strategies that utilize healthcare visits may be most effective, because children with SCA have at least 8 times as many healthcare encounters per year versus those without SCA.¹

Reference

1. Reeves SL, Jary HK, Gondhi JP, Kleyn M, Wagner AL, Dombkowski KJ. Pneumococcal vaccination coverage among children with sickle cell anemia, sickle cell trait, and normal hemoglobin. Pediatr Blood Cancer. 2018;65(10):e27282. doi: 10.1002/pbc.27282.