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Vaccine reduced bacterial illnesses in children who have sickle cell disease
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Rates of invasive pneumococcal disease in children aged younger than 5 years with sickle cell disease decreased 93.4% after the pneumococcal conjugate vaccine was introduced in 2000, according to a new study published in Clinical Infectious Diseases.
Invasive pneumococcal disease is the leading cause of mortality among children with sickle cell disease. Compared with the general population, patients with sickle cell disease are between 30 and 600 times more likely to develop pneumococcal meningitis, bloodstream infection or other serious infections.
The researchers were not surprised by the decrease in invasive pneumococcal disease among vaccinated children with sickle cell disease, but were surprised by the magnitude of the reduction.
“That number says that the vaccine is doing well in a high risk population and is efficacious in preventing serotypes that are contained within the vaccine,” Natasha Halasa, MD, MPH, assistant professor of pediatric disease at Vanderbilt University School of Medicine and one of the study’s researchers, told Infectious Diseases in Children. “I was surprised that it was over 90% effective because there are other serotypes out there that are not covered by the seven-valent vaccine.”
PCV7 vaccine
The pneumococcal conjugate vaccine (PCV7, Prevnar, Wyeth) is recommended for all children aged younger than 2 years and for selected children aged 2 to 4 years with high risk conditions, including sickle cell disease.
Prior to the pneumococcal conjugate vaccine, children with sickle cell disease were given penicillin prophylaxis to thwart infections, which showed an 84% decrease of invasive pneumococcal disease, according to the findings of a prior study.
This vaccine is administered at routine checkup ages.
“Since all kids are supposed to get this vaccine at 2 months, 4 months, 6 months of age and then again at 12 months, children with sickle cell are now receiving this benefit at such an early age when the rates of pneumococcal disease are so high. They used to have to wait until 2 years of age for the other pneumococcal vaccine. Therefore, in the first two years of life, you had to rely on parents giving their children daily penicillin prophylaxis,” Halasa said. “And even when parents were compliant, there was a worry that the bacteria may be resistant to penicillin.”
The researchers are cautious, however, because of concern about new pneumococcal serotypes that are not covered in the vaccine emerging and causing disease.
Infection rates tracked
Rates were analyzed for all children with sickle cell disease in Tennessee’s Medicaid program before and after the introduction of the vaccine. The study population (n=2,026) included individuals with sickle cell disease who were enrolled in Tennessee Medicaid from January 1995 to December 2004. This population represented 13,687 person-years of follow-up. The researchers used person-years to compare cohorts for the pre- and post-vaccine periods.
Population-based surveillance data used to identify individuals with invasive pneumococcal disease were linked to patients with sickle cell in the state Medicaid database to determine incidence rates.
Disease rates drop
Of 2,026 people with sickle cell disease, 37 developed invasive pneumococcal disease. Twenty-one were in children aged younger than 5 years. Comparing the years before the vaccine, 1995 to 1999, with data from years after the vaccine was available, 2001 to 2004, invasive pneumococcal disease rates decreased 90.8% in children younger than 2 years. Cases dropped from 3,630 to 335 cases per 100,000 person years (P<.001).
In children aged younger than 5 years, rates decreased 93.4%, from 2,044 to 134 cases per 100,000 person-years (P<.001). Among children with sickle cell aged 5 years or older, invasive pneumococcal disease rates decreased from 161 cases per 100,000 person-years before the vaccine to 99 cases per 100,000 person-years after the vaccine was available. – by Kirsten H. Ellis
For more information:
- Halasa NB, Shankar SM, Talbot TR, et al. Incidence of invasive pneumococcal disease among individuals with sickle cell disease before and after the introduction of the pneumococcal conjugate vaccine. Clin Infect Dis. 2007;44:1428-1433.