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Up to 50% of acute otitis media is caused by pneumococci. Conjugate vaccines, you would think, should be able to make inroads into this number and the morbidity and economic costs associated with the disease. A trial in Finland (New England Journal of Medicine2001;344:403–9), however, has shown no clear cut reduction in the total number of cases. A total of 1662 infants were randomised to receive either heptavalent pneumococcal polysaccharide conjugate vaccine (conjugated with the non-toxic diphtheria toxin analogue CRM 197) or hepatitis B vaccine (controls) along with routine vaccines at 2, 4, 6, and 12 months of age. They were followed up for between six and 24 months, during which time there were 1251 episodes of acute otitis media in the pneumococcal vaccine group and 1345 in the controls. The rate of acute otitis media was 1.16 episodes/child-year in the pneumococcal vaccine group and 1.24 episodes/child-year in the control group (vaccine efficacy 6% (95% confidence interval −4% to +16%)). (A Californian trial of the same vaccine had shown an efficacy of 7% against acute otitis media.) There were 414 episodes of pneumococcal acute otitis media (confirmed by culture of middle ear fluid) in the control group and 271 in the pneumococcal vaccine group (34% reduction). Acute otitis media caused by vaccine serotypes was reduced by 57% and that caused by cross-reacting serotypes by 51%. Acute otitis media caused by other serotypes of pneumococci was increased by 33% in the pneumococcal vaccine group. Recurrent acute otitis media was reduced by 9% overall. The conjugate vaccine reduced the occurrence of acute otitis media caused by vaccine serotypes and cross-reacting serotypes and possibly reduced the total number of episodes of acute otitis media. They calculated that the vaccine could prevent 1.2 million cases of acute otitis media in the USA each year (but the 95% confidence limits range from 3.2 million cases prevented to 0.8 million cases caused). Use of the vaccine was followed by an increase in acute otitis media caused by non-vaccine, non-cross-reacting, pneumococcal serotypes.
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