PROPHYLACTIC IMMUNIZATION OR VACCINATION 691 



A comparison of these tables shows that the general reaction is much 

 more infrequent or milder in children than in adults, even after the first 

 dose; after the second and third doses the difference is more marked. 



In former years considerable stress was laid upon the possibility of 

 a negative phase following the inoculation, during which a person was 

 believed to be more susceptible to infection. This is now believed by 

 Leishman, Russel, and others of extended experience to be incorrect, 

 the more general belief being that inoculations may be made and are 

 especially indicated during epidemics of the disease. 



Duration and Degree of Typhoid Immunity. It should be empha- 

 sized that immunity following typhoid immunization is not absolute, 

 and an immunized person cannot afford to neglect ordinary precautions 

 against infection. A lowered state of general body health or a large dose 

 of infectious material may at any time result in infection. 



The prophylactic treatment should be used in conjunction with 

 well-known sanitary precautions in order to obtain the best results. 



The immunity is apparently manifest soon after the first and second 

 doses have been given. The duration is not known definitely. From 

 the rich experience of the British army in India Colonel Firth l concludes 

 that immunity begins to decline in about two and one-half years after 

 inoculation. However, even after four and five years the typhoid rate 

 among the inoculated is, estimated roughly, one-fourth that of unpro- 

 tected troops. 



Sensitized Typhoid Vaccine of Gay and Claypool. Gay and Clay- 

 pool, 2 who have made an extended and extensive study of typhoid im- 

 munization, have advocated a polyvalent, sensitized typhoid vaccine 

 sediment for prophylactic immunization against typhoid fever, as being 

 superior to other forms of typhoid vaccine. Force 3 has found that this 

 vaccine produces less reaction and Sawyer 4 has found it more protective 

 than several other types of commercial vaccine. Gay's vaccine consists, 

 of the ground sediment of a mixed polyvalent vaccine that has been 

 sensitized by an antityphoid serum and then killed and precipitated 

 by alcohol. From this ground culture the endotoxins are extracted 

 by carbolated saline solution and the remaining sediment of bacterial 

 bodies alone used for prophylaxis and in the treatment of typhoid fever. 



For prophylactic purposes yV nig. of dried bacteria, which corresponds 



1 Jour. Roy. Army Med. Corps, 1911, xvi, 589. 



2 Archiv. Int. Med., 1913, xii, 613; 1913, xii, 622; 1914, xiii, 471; 1914, xiv, 602; 

 1914, xiv, 662, 669, and 671; 1916, xvii, 303. 



3 Amer. Jour. Pub. Health, 1913, iii, 750. 



4 Jour. Amer Med. Assoc., 1915, Ixv, 1413. 



