Hong Kong Journal of Paediatrics [HK J Paediatr (New Series) 2001;6:131]

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HK J Paediatr (New Series)
Vol 6. No. 2, 2001

HK J Paediatr (New Series) 2001;6:131

Proceedings of The First Current Topic in Infectious Diseases

Overview of Conjugate Pneumococcal Vaccine: Serotype Coverage, Efficacy and Status of Usage in other Countries

Samson SY Wong

HK J Paediatr (new series) 2001;6:127-132

Proceedings of The First Current Topic in Infectious Diseases: Consensus Meeting on Conjugate Vaccines of the Center of Infection
Faculty of Medicine, The University of Hong Kong (Selected Abstracts)

Streptococcus pneumoniae remains a major cause of morbidity and mortality even in the developed countries. It is one of the commonest causes of community-acquired pneumonia, bacteraemia, meningitis, acute otitis media, sinusitis, and postsplenectomy sepsis.⁶ Currently available vaccines target the polysaccharide capsule, whose antiphagocytic property is a major virulence factor. Of the 90 described capsular types, the 23 commonest types are included in the polysaccharide vaccine, which provides coverage against 80% to 90% of bacteraemic isolates.^7,8 The polysaccharides, however, are poorly immunogenic in children less than two years of age that are most susceptible to invasive pneumococcal infections. Pneumococcal polysaccharides are therefore conjugated to proteins to improve their immunogenicity in young children and infants. A heptavalent conjugate pneumococcal vaccine was licensed in 2000 in the United States, which contains serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F. CRM₁₉₇, a non-toxic variant of diphtheria toxin, is used as the protein conjugate. These seven serotypes accounted for 86% of bacteraemia, 83% of meningitis, and 65% of acute otitis media in children less than six years of age in the United States. In a randomized, double-blinded clinical trial in which ~37,000 children were recruited, the heptavalent vaccine is ~100% effective in preventing invasive pneumococcal infections caused by vaccine serotypes and 89% against all serotypes. There is a 7.0%-22.8% reduction in the incidence of otitis media and a 5.3% reduction in antibiotic use in the vaccinees. The vaccine is presently licensed for use in infants older than six weeks and is given at two, four, six months, with a booster dose at 12-15 months. It is recommended for children less than 23 months old; for children aged 24-59 months, it should be considered for those who are predisposed to severe pneumococcal disease. A 40%-50% reduction in nasopharyngeal pneumococcal carriage of vaccine serotypes is found in field trials of a 9-valent conjugate vaccine.

Method and Process of Consensus Building

The consensus meeting on Consensus meeting on conjugate vaccines was held on February 17, 2001, as the first current topic in infectious diseases that was organized by the Centre of Infection, the University of Hong Kong. A panel of experts from the fields of Internal Medicine, Clinical Microbiology, Internal Medicine, Paediatrics and Public Health were provided with the latest scientific papers^1-8 and were invited to speak and discuss on various aspects concerning the topic.

After the formal presentation, panel discussion was held. All speakers, invited discussants from various aspects of the medical fields and audiences actively participated in the discussion with further elaboration on issues around S. pneumoniae and H. influenzae disease burden, antimicrobial resistance and conjugate vaccine.

Finally, conclusions were drawn on the basis of the current scientific information and views expressed by the panel and other participants. Drafts in progress and final copies of the manuscript were distributed to panel for comments before submission for publication.

Consensus Panel Members

Daniel CS Chiu, Pediatrician in private practice
Susan SS Chiu, Assistant Professor, Department of Paediatrics, The University of Hong Kong
CB Chow, Consultant, Department of Paediatrics, Princess Margaret Hospital
PL Ho, Associate Professor, Department of Microbiology, The University of Hong Kong
YL Lau, Chair Professor in Paediatrics, Department of Paediatrics, The University of Hong Kong
CW Leung, Consultant, Department of Paediatrics, Princess Margaret Hospital
Dominic NC Tsang, Consultant, Department of Clinical Pathology, Queen Elizabeth Hospital
Kenneth WT Tsang, Associate Professor, Department of Medicine, University of Hong Kong.
Thomas HF Tsang, Community Physician, Department of Health
Samson SY Wong, Assistant Professor, Department of Microbiology, University of Hong Kong.
YH Yang, Professor, Beijing Children's Hospital, Beijing
KY Yuen, Chair Professor in Infectious Diseases, Department of Microbiology, The University of Hong Kong

Consensus Statements

Disease burden of paediatric Haemophilus influenzae type b infections in Hong Kong

1. The incidence of Haemophilus influenzae type b (Hib) diseases in Hong Kong appears to be low. Multiple confounding factors, such as prior antibiotic usage, might be the causes for the apparent low recorded prevalence.

2. Further study to collect epidemiological data in Hong Kong would be difficult due to the following factors:

a) Some children might have been given Hib vaccination on an individual basis.

b) There are quite a number of patients taking antibiotics prior to collection of specimens for cultures and the recovery rate of any microorganisms in these situations is relatively low.

3. Gaps in existing data should be addressed in future studies using new research methodology, such as the WHO rapid assessment tool.

Use of conjugate Haemophilus influenzae type b vaccine

1. Conjugate Hib vaccine has proven safety and efficacy in prevention of invasive Hib disease.

2. Thorough cost-effective/benefit/utility analysis and comparison of existing program would be very helpful in supporting recommendation for universal vaccination in this locality. Broader discussion/consultation on what constitute the "acceptable" cost is required.

Disease burden of pneumococcal infections in Hong Kong

1. Disease burden of pneumococcal disease is still unclear and further study would be needed for different at-risk groups.

2. Penicillin-resistant and multiple antibiotic-resistant pneumococci are a major problem in Hong Kong.

Use of conjugate pneumococcal vaccine

1. The heptavalent conjugate vaccine provides good coverage of the serotypes causing invasive pneumococcal disease in Hong Kong at present.

2. Conjugate pneumococcal vaccine is effective in decreasing vaccine strain carriage, and preventing invasive pneumococcal disease in young children from published experience.

Acknowledgement

The meeting was sponsored by the Hong Kong Paediatric Foundation.

References

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6. American Academy of Pediatrics. American Academy of Pediatrics. Committee on Infectious Diseases. Policy statement: recommendations for the prevention of pneumococcal infections, including the use of pneumococcal conjugate vaccine (Prevnar), pneumococcal polysaccharide vaccine, and antibiotic prophylaxis. Pediatrics 2000;106: 362-6.

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