290 THE PRINCIPLES OF IMMUNOLOGY 



the rates for previous wars, but also below the rate found in civil life in 

 some of the older states where the entire population is protected by all 

 the sanitary measures of modern life." 



At the beginning of the World War, of the troops in Belgium only 

 those of the British Army were adequately protected. At the beginning 

 of trench warfare in 1914 an epidemic broke out, and in January and 

 February of 1915, 4000 cases occurred in Dunkirk. Up to May of 1915 

 only 827 cases were contributed from the British Army, the bulk of the 

 cases came from among the unvaccinated Belgian soldiers and civilians. 

 Vaccination was instituted in February, and the epidemic was at an 

 end by the middle of the summer. In the early days of the war vac- 

 cination had not been compulsory in the French Army, and as the 

 result a large number of troops were victims of typhoid fever. The 

 institution of vaccination completely altered the picture. Courmont 

 gives the following statistics for the French Army in 1916: 



Deaths 



Non-vaccinated cases 17.4 per cent. 



Of the vaccinated cases: 



Those who had one injection 6.0 per cent. 



Those who had two injections 4.0 per cent 



Those who had three injections 2.5 per cent. 



Those who had four injections 1.9 per cent. 



Duration of Protection. When typhoid vaccination was first in- 

 troduced it was generally assumed that protection lasts for about two 

 years. Certain British troops in Mudros were found to have developed 

 typhoid fever within six months after inoculation. Similarly, certain 

 troops of the American Army developed typhoid fever a few months 

 after they had been vaccinated, but it was found upon investigation 

 that in this instance the vaccination had not been completed. On the 

 basis of experience, yearly vaccinations were practiced in the British 

 Army, although it was not considered necessary to give the three 

 doses at the time of revaccination ; a single maximum dose on revac- 

 cination apparently served to maintain immunity. Yearly revaccina- 

 tion, however, provides adequate protection. Knowing that infection 

 has occurred within a few months after proper vaccination it is no 

 longer advisable to state that protection lasts for more than a year. 

 The determination as to when revaccination must be practiced depends 

 in certain measure upon the degree of exposure to the disease. In 

 those districts where typhoid or paratyphoid fevers are endemic, we rec- 

 ommend that vaccination be reinforced by a single yearly inoculation of 

 the maximum dose. If a period of two years has elapsed since previous 

 vaccination, it is advisable to revaccinate with three injections. 



Complications. The reaction to any dose of typhoid vaccine is 

 extremely variable. Usually the second and third doses produce some- 

 what more severe reactions than the first dose. There are, however, 

 certain individuals who are apparently hypersusceptible to typhoid pro- 

 tein, and these may react with great severity. As a rule, reactions are 

 merely local and are exhibited by swelling, redness, tenderness and pain 

 about the site of inoculation. General reactions are much less fre- 



