Accelerated immunisation with diphtheria-tetanus-pertussis vaccine SIR,-It is not surprising that Dr Mary E B Ramsay and colleagues found a satisfactory response to diphtheria and tetanus toxoids in children who had been vaccinated at 3, 4, and 5 months.' This has been a popular schedule for giving diphtheria-tetanus-pertussis vaccine in many countries, and its use in countries such as Bulgaria, Czechoslovakia, Hungary, and Poland has also brought the incidence of whooping cough to extremely low levels.2 Dr Ramsay and colleagues' report is less reassuring, however, about the future with respect to pertussis. At present it is wishful thinking for them to say: "It is unlikely that a 2, 3, 4 month schedule will be less immunogenic than a 3, 4, 5 month schedule." Firm evidence of this is required because if the first dose is given too early it depresses the response to subsequent doses. The question that has to be answered is whether 2 months of age is too early for the first dose. Equally important is the nature of the tests that should be used to assess the response to pertussis antibodies. Dr Ramsay and colleagues did three tests. They looked for antibody to filamentous haemagglutinin and to pertussis toxin, each of which has been shown not to correlate with protection of children.4 They also performed a single enzyme linked immunosorbent assay (ELISA) with "agglutinogens 2 and 3"; yet the epitopes involved in such ELISAs may differ from those responsible for bacterial agglutination on which the evidence of type specific immunity in pertussis is based.5 Moreover, a test that detects either agglutinin 2 or agglutinin 3 is inadequate: children need both of these antibodies, and various countries have experienced failure of vaccine when one or the other response has been deficient.6 British and several other whole cell vaccines contain the necessary agglutinogens; they provide excellent immunity when given at 3, 4, and 5 months. I await Dr Ramsay and colleagues' findings in their "prospective study of the immediate and long term antibody responses to the new 2, 3, and 4 month schedule" now in progress. NOEL W PRESTON
Pertussis Reference Laboratory, University Medical School, Manchester M 13 9pT I Ramsay MEB, Corbel MJ, Redhead K, Ashworth LAE, Begg NT. Persistence of antibody after accelerated immunisation with diphtheria/tetanus/pertussis vaccine. B.MJ 1991;302: 1489-91. (22 June.) 2 World Health Organisation. Fifth meeting of the European advisory group on the expanded programme on immunization. Copenhagen: WHO Regional Office for Europe, 1991:5-6. (WHO report EURIICP/EPI 026.) 3 Baraff LJ, Leake RD, Burstyn DG, Payne T, Cody CL, Manclark CR, et al. Immunologic response to early and routine DTP immunization in infants. Pediatrics 1984;73:37-42. 4 Ad Hoc Group for the Study of Pertussis Vaccines. Placebocontrolled trial of two acellular pertussis vaccines in Swedenprotective efficacy and adverse events. Lancet 1988;i:955-60. S Preston NW. Some unsolved problems with vaccines. Progress in Drug Research 1979;23:9-26. 6 Preston NW. Pertussis today. In: Wardlaw AC, Parton R, eds. Pathogenesis and immunity in pertussis. Chichester: Wiley, 1988:1-18.
ing urea labelled with carbon-14 as a non-invasive method of documenting our success (or otherwise) in eradicating H pylori infection.' We originally suggested that a two hour area under the curve of