Prevention of wound infection.

Discussion It is not easy to reconcile these findings with those obtained in the early days of diphtheria immunization when F.T. was extensively used with definite clinical success. It is possible that the reason for the poor immunizing action of the present-day F.T. is the fact that it is prepared in a highly purified form, whereas the F.T. used in the early days undoubtedly contained many impurities which might well have exerted an adjuvant effect. There is also a discrepancy between our findings and those reported by Bousfield and Holt (1954), who obtained better Schick-conversion rates in children after two spaced doses of 30 Lf of F.T. This discrepancy can, however, be explained on the basis of the difference in immunizing procedures. Whereas Bousfield and Holt always Schick-tested the children before immunizing them this was not done in our trials. Recently Bousfield and Holt (1962) have shown that better Schick-conversion rates can be obtained if children are Schick-tested before being immunized, particularly if the testing is done four weeks rather than one week before the injection of F.T. This effect is presumably due to the additional antigenic stimulus provided by the Schick-test dose. From the results of our study it is concluded that diphtheria plain F.T. as prepared at the present time in a highly purified form is not suitable for primary immunization against diphtheria. In order to obtain adequate primary immunization with such a purified antigen it is essential that it should be combined with an adjuvant such as pertussis vaccine or a mineral carrier. It would thus seem desirable to give young children a combination of pertussis vaccine with diphtheria and tetanus toxoids (triple vaccine), and to older persons who have not previously been immunized a combination of diphtheria and tetanus toxoids containing a mineral carrier such as aluminium hydroxide or phosphate. Although it might be argued that such combinations carry a slight risk of provocation to polio-myelitis, now that vaccination against poliomyelitis is practised on a wide scale the risk is much less than in past years and will not become more frequent if the prevalence of poliomyelitis in the population remains low. If the triple vaccine is given after immunization with the poliomyelitis vaccine, as in Schedule Q of the Ministry of Health's Circular (1961), the risk should be almost negligible. Summary Field trials of diphtheria plain formol toxoid (F.T.) in children 6 to 12 months …