Effect of dosage on immunogenicity of a Vi conjugate vaccine injected twice into 2- to 5-year-old Vietnamese children.
In a double-blind, randomized, and placebo-controlled previous trial, the efficacy of Vi-rEPA for typhoid fever in 2- to 5-year-olds was 89.0% for 46 months. Vi-rEPA contained 25 microg of Vi and induced a greater-than-eightfold rise in immunoglobulin G (IgG) anti-Vi in all of the vaccinees tested. In this investigation, we conducted a dosage-immunogenicity study of 5, 12.5, and 25 microg of Vi-rEPA in this age group. Two doses of Vi-rEPA were injected 6 weeks apart. Blood samples were taken before and at 10 weeks (4 weeks after the second injection) and 1 year later. All postimmunization geometric mean (GM) levels were higher than the preimmune levels (P < 0.0001). At 10 weeks, the GM IgG anti-Vi level elicited by 25 microg (102 EU/ml) was higher than those elicited by 12.5 microg (74.7 EU/ml) and 5 microg (43 EU/ml) (P < 0.004): all of the children had > or = 3.52 EU/ml (estimated minimum protective level). One year later, the levels declined about sevenfold (13.3 and 11.3 versus 6.43 EU/ml, P < 0.0001) but remained significantly higher than the preimmune levels (P < 0.0001), and >96% of the children had a greater-than-eightfold rise. This study also confirmed the safety and consistent immunogenicity of the four lots of Vi-rEPA used in this and previous trials.
Canh
Do Gia
DG
Diarrhea Diseases Epidemiology and Field Research Section, National Institute of Hygiene and Epidemiology, Hanoi, Veitnam.
Lin
Feng-ying Kimi
FY
Thiem
Vu Dinh
VD
Trach
Dang Duc
DD
Trong
Nguyen Dinh
ND
Mao
Nguyen Duc
ND
Hunt
Steven
S
Schneerson
Rachel
R
Robbins
John B
JB
Chu
Chiayung
C
Shiloach
Joseph
J
Bryla
Dolores A
DA
Bonnet
Marie-Claude
MC
Schulz
Dominique
D
Szu
Shousun C
SC
D036002:ADP Ribose Transferases / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology; D000907:Antibodies, Bacterial / Q000097:blood*; D001427:Bacterial Toxins / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology; D002675:Child, Preschool; D004306:Dose-Response Relationship, Immunologic; D004311:Double-Blind Method; D005098:Exotoxins / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D008297:Male; D011135:Polysaccharides, Bacterial / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology*; D012485:Salmonella typhi / Q000276:immunology*; D014435:Typhoid Fever / Q000517:prevention & control; D014436:Typhoid-Paratyphoid Vaccines / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology*; D018074:Vaccines, Conjugate / Q000008:administration & dosage / Q000009:adverse effects / Q000276:immunology; D014744:Vietnam; D037521:Virulence Factors / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology; D000097668:Pseudomonas aeruginosa Exotoxin A
D036002:ADP Ribose Transferases; D000907:Antibodies, Bacterial; D001427:Bacterial Toxins; D005098:Exotoxins; D007074:Immunoglobulin G; D011135:Polysaccharides, Bacterial; D014436:Typhoid-Paratyphoid Vaccines; D018074:Vaccines, Conjugate; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A; C057664:Vi polysaccharide vaccine, typhoid