Pneumococcal Vaccine Works on Virulent Strains

Laird Harrison

October 11, 2013

SAN FRANCISCO — The introduction of a vaccine targeting some of the most virulent pneumococcal serotypes has reduced the proportion of children infected with invasive pneumococcal disease caused by those serotypes, according to a new study.

"This is very good news," said study coauthor Tina Tan, MD, professor of pediatrics and infectious diseases at Northwestern University in Chicago.

Lead author John McLaughlin, PhD, an epidemiologist at Pfizer, the manufacturer of the pneumococcal conjugate vaccine known as PCV13, presented the results here at IDWeek 2013.

The US Centers for Disease Control and Prevention recommends PCV13 for all children younger than 5 years of age and for adults with certain risk factors.

After the introduction of a 7-valent pneumococcal conjugate vaccine (PCV7) in the United States in early 2000, the rate of invasive pneumococcal disease in young children dropped about 70%.

But serotypes not targeted in that vaccine caused more infections than they had in the past. There was an increase in infections caused by serotype 19A, which is linked to a large proportion of antibiotic-resistant infections.

The US Food and Drug Administration has already approved the 13-valent PCV13, which targets the 7 serotypes in PCV7 plus serotypes 1, 3, 5, 6A, 7F, and 19A.

To assess the effectiveness of PCV13, Dr. McLaughlin's team collected data from at 8 geographically dispersed children's hospitals that make up the US Pediatric Multicenter Pneumococcal Surveillance Group.

The researchers used positive cultures from a normally sterile site — such as blood or cerebrospinal, pleural, synovial, or peritoneal fluid — to document infections.

Table. Invasive Pneumococcal Disease Caused by PCV13-Targeted Serotypes

Year 19A Serotype, % Other PCV13 Serotypes, %
2008/2009 37 66
2010 37 62
2011 28 48

 

The reductions played out differently, depending on the age of the children.

For babies younger than 2 years, the proportion of invasive disease caused by PCV13 serotypes dropped 44% from 2008/2009 to 2011 (P < .01).

In children 2 to 17 years of age, the decrease in the proportion of invasive disease caused by these serotypes was only 17%, and was not statistically significant (P = .12).

The difference in the 2 age groups was largely attributed to serotype 19A, which caused a smaller proportion of disease in babies after the vaccine's introduction, but a steady proportion in older children, the researchers report.

They speculate that the vaccine was less effective in older children because fewer older children were vaccinated. Although older children might have benefited indirectly from the vaccination of younger children against other serotypes, serotype 19A is particularly virulent, they point out.

The solution might be more vaccination of older children, said Dr. Tan. "Clinicians need to be aware of this so that infants and children get all the recommended doses," she added.

Creating new vaccines targeting pneumococcal bacteria is a "cat and mouse game" because the bacteria continue to evolve, said Nicholas Gross, MD, from Loyola University Chicago in Maywood, Illinois.

These data "do not suggest that there is any particular breakthrough," he noted.

In addition, there are limitations when comparing outbreaks from one year to the next because other factors, such as the weather and poverty rates, can affect the patterns of infection, Dr. Gross pointed out.

This study was funded by Pfizer. Dr. McLaughlin is an employee and shareholder of Pfizer. Dr. Tan and Dr. Gross have disclosed no relevant financial relationships.

IDWeek 2013: Abstract 443. Presented October 3, 2013.

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