Hib vaccination: breakthrough in The Gambia

Routine Haemophilus influenzae type b (Hib) vaccination of infants in The Gambia began in May 1997 after a successful clinical trial. What impact has the vaccine had? Surveillance in the western half of the country shows an impressive fall in Hib disease rates.

Success in a clinical trial does not guarantee that a vaccine will be effective in routine use. Poor storage and transport conditions can reduce vaccine efficacy. By contrast, ‘herd immunity’ can make vaccination more effective in a larger population. Finally, widespread immunisation can change disease patterns. Researchers from the Medical Research Council Laboratories in Banjul investigated all these possible effects of the Gambian programme.

Between May 1997 and April 2002, they checked 5,984 children for possible Hib infections. Forty-nine had Hib disease of whom 36 had meningitis, eight had pneumonia and five had septicaemia. The researchers found that:

• Fifty-seven percent of Hib cases had not received the vaccine, 35 percent had received only one dose, four percent had received two doses and four percent had received three doses.
• The number of children with Hib meningitis decreased from 36-40 cases per year before the vaccine was introduced, to 22 in 1997/8 and three in 2001. No cases of Hib disease have been identified in the western region since 2002.
• The annual incidence rates of Hib meningitis dropped from over 200 per 100,000 children under one year before any use of the vaccine to zero in 2002 and from 60 to zero cases per 100,000 children under five years old.
• Over the same period, the proportion of healthy children carrying the Hib bacterium dropped from 12 to 0.25 percent.
• The estimated vaccine efficacy against meningitis after two doses was 93 percent and there was no apparent benefit from an extra dose. Efficacy after a single dose was only 35 percent and not statistically significant.
• Routine use of Hib vaccination has not led to unexpected forms of Hib disease in children over two years.

Two doses of vaccine were needed for direct protection from Hib disease. But most children had their second dose too late to be protected directly. Most of the reduction in disease rates is likely to be due to indirect effects, probably because there are fewer carriers.

Routine immunisation was stopped from time to time because of a meningitis vaccination campaign and irregular supplies of vaccine. Despite this, vaccination has cut the spread of Hib almost to zero. The researchers draw the following conclusions for health policy in The Gambia and other countries:

• Virtual elimination of Hib disease is possible in a developing country setting with an immunisation programme that is effective but not perfect.
• Surveillance will be needed where booster jabs are not given, to ensure that the effect of national immunisation with Hib vaccine is sustained.

Source(s):
‘Elimination of Haemophilus influenzae type b (Hib) disease from The Gambia after the introduction of routine immunisation with a Hib conjugate vaccine: a prospective study’, The Lancet 366, pages 144-150, by Richard A. Adegbola, et al., 2005 Full document.

Funded by: World Health Organisation, UK Medical Research Council

id21 Research Highlight: 23 February 2006

Further Information:
Richard Adegbola
MRC Laboratories
PO Box 273
Banjul
The Gambia

Tel: +220 4494491
Fax: +220 4497924
Contact the contributor: radegbola@mrc.gm

Medical Research Council Laboratories, The Gambia

Other related links:
'Testing a vaccine for childhood pneumonia in the Gambia'

'Simple guidelines target antibiotic treatment in Kenyan children'

'Adverse effects of mass vaccination in Brazil: the case of MMR'

'Two drugs are better than one – or three – for cryptococcal meningitis'

'Rapid response – diagnosing bacterial meningitis in primary healthcare settings'

The Gambia Pnuemococcal Vaccine Trial

WHO media factsheet: Haemophilus influenzae type B (HiB)