February 1996
SAN FRANCISCO—The new generation of pneumococcal vaccines may serve double duty: while protecting infants against disease, they may also reduce nasopharyngeal carriage of antibiotic-resistant pneumococci.
Whereas polysaccharide pneumococcal vaccines are not immunogenic in children younger than 2 years, the vaccines in development are conjugated to protein carriers and are expected to be effective in infants.
Research, however, is suggesting that the conjugated pneumococcal vaccines will also effectively reduce nasopharyngeal carriage of pneumococci and the spread of antibiotic-resistant bacteria.
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A study by researchers from Ben-Gurion University, Beer-Sheva, Israel, compared the effects of one and two doses of a heptavalent conjugated vaccine (containing serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F) with a single dose of polysaccharide vaccine.
The study population included 263 healthy children between 12 and 18 months of age divided into three groups: 97 children received one dose of the conjugated vaccine; 68 children received a single dose of polysaccharide vaccine; and 98 children received two doses of conjugated vaccine 3 months apart. All doses were given over a 5-month period to avoid seasonal variations.
Nasopharyngeal cultures were taken before immunization and 1 month, 3 months, and 1 year after immunization.
Prior to immunization, nasopharyngeal carriage of pneumococci—both antibiotic resistant and susceptible strains—was prevalent. More than half (57%) of the isolates were of types contained in the heptavalent vaccine. The vaccine serotypes most commonly found were, in decreasing order, 23F, 6B, 19F, 14, 18C, and 4.
A significantly greater percentage of the vaccine serotypes were resistant to antibiotics compared with serotypes not included in the vaccine, especially when resistance to two or more antibiotics was considered. Therefore, the researchers hypothesized that if the heptavalent conjugated pneumococcal vaccine effectively reduces nasopharyngeal carriage of all vaccine serotypes, it will also reduce carriage of a significant proportion of antibiotic-resistant serotypes.
As expected, nasopharyngeal carriage of nonvaccine serotypes was unaffected, and no difference was found in the carriage rates of vaccine serotypes among the three study groups 1 month after immunization. This finding was consistent with the Haemophilus influenzae type b conjugate vaccine experience.
A reduction in nasopharyngeal carriage was seen, however, 3 months after immunization among the groups that had received one or two doses of conjugated pneumococcal vaccine. The reduction persisted 1 year after immunization. When evaluated separately, antibiotic-resistant vaccine serotypes followed a similar pattern.
For more information, see:
- Dagan R, Muallem R, Yagupsky P. Reduction of nasopharyngeal carriage of penicillin-resistant pneumococci by pneumococcal-OMPC conjugate vaccine during second year of life. Abstract #G2, presented at the 35th Interscience Conference on Antimicrobial Agents and Chemotherapy, San Francisco, Calif., Sept. 17-20, 1995.
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