Vaccine Not Always Enough to Prevent Pneumococcal Disease

Invasive pneumococcal disease in children not always covered by current vaccine

(RxWiki News) Vaccines can be used to protect against both viruses and bacteria. But bacteria have a secret weapon that makes them harder to fight.

Bacteria can have different strains, or "serotypes," that can make humans sick. This trick means that vaccines usually have to be designed to address as many of the different serotypes for bacterial illnesses as possible.

With invasive pneumococcal disease, the current vaccine in the US protects against 13 serotypes, but children are still getting sick from the other strains, a recent study found.

"Discuss the CDC recommended immunization schedule with your child's pediatrician."

This study, led by Pui-Ying Iroh Tam, MD, of  the University of Minnesota Children’s Hospital in Minneapolis, looked at the different serotypes of invasive pneumococcal disease in children before and after the current vaccine.

"Serotypes" are different strains of bacteria. The current vaccine, PCF13, protects against 13 strains, but there are others that cause pneumococcal disease.

The researchers collected information from Massachusetts state public health records on children 5 years old and younger who suffered from invasive pneumococcal disease from 2007 to 2012.

During 2007 to 2009, before the PCV13 vaccine had been introduced, there were 168 cases of pneumococcal disease.

There were then 85 cases from 2010 to 2012, the time period when the PCV13 vaccine was available.

Illnesses caused by the bacterial strains covered by the disease dropped by 18 percent in the first two years after the vaccine became available.

However, slightly more children were hospitalized for pneumococcal disease during the latter two years.

While 51 percent of children with the disease were hospitalized before the vaccine became available, 58 percent of the children who got sick were hospitalized in the two years after the vaccine was out.

It's not clear that this was an increase, however, since the small numbers of children involved meant the higher hospitalization rate could be due to chance.

However, the overall number of children hospitalized was still lower after the vaccine was out since there were fewer sick children.

Approximately 86 children were hospitalized before the vaccine was released, and 49 children were hospitalized after the vaccine was out.

Among the children hospitalized, 24 percent of those after the vaccine's introduction had underlying conditions, compared to 20 percent before the vaccine.

It seemed the serotypes not protected by the vaccine were also the ones disproportionately affecting children with underlying conditions.

While 28 percent of children with underlying conditions became sick with a bacterial strain not covered by the vaccine, only 17 percent of children without underlying condition got sick from a strain not covered by the vaccine.

Unsurprisingly, children with underlying conditions were also more likely to be hospitalized.

Half of children without underlying conditions were hospitalized, compared to 80 percent, or four of every five children with underlying conditions, who were hospitalized.

Children with underlying conditions were also more likely to spend more time in the hospital than children without secondary infections or conditions.

"Initial data suggest that non-vaccine serotypes are more common in children with underlying conditions, who have greater morbidity from disease," the authors concluded.

However, there were no differences in the rates of deaths among children before and after the vaccine's introduction.

"Routine vaccination with PCV13 may not be enough to reduce the risk in patients with comorbidity," the authors wrote.

The study was published July 7 in the journal Pediatrics. The research was funded by Pfizer, Inc. and the National Institutes of Health.

In addition to the Pfizer grant for this study, one author has served on advisory boards regarding the pneumococcal vaccine for GSK Biologicals and Pfizer and has received other research grants from Pfizer and Merck. No other potential conflicts of interest were reported.

Review Date: 
July 6, 2014