DELAYED-TYPE HYPERSENSITIVITY RESPONSE AFTER FIVE
YEARS OF BCG VACCINATION IN CHILDREN FROM 0 TO 15 YEARS OLD IN HOCHIMINH CITY
Mai Nguyet Thu Hong
Pasteur Institute in HCHC
Delayed-Type Hypersensitivity (DTH) response after BCG vaccination was observed for evaluating the vaccine efficacy. After an observation on 800 children from 0 to 15 years old in the Pasteur Institute of HoChiMinh city, we obtained 60.25% of individuals having the DTH positive response five years after the vaccination.
These 800 children, except tuberculosis infection, were classified as follows:
Table 1. Classification of children
|
|
Number of children |
||
|
0 – 5 years old |
> 5 - 10 years old |
> 10 – 15 years old |
|
|
BCG 1 |
100 |
100 |
100 |
|
BCG 2 |
100 |
100 |
100 |
|
BCG 3 |
|
100 |
100 |
Plan of vaccination, revaccination and observation:
Vaccination:
The
intradermic injection was applied with 0.05 mg of BCG vaccine for children under
1 year old and 0.1 mg for children older than 1 year. For the children above 3
months, the DTH test was realized preliminarily for the vaccination.
The
response was considered as positive when the induration exhibited a diameter
larger than 6 mm. DTH response was recorded at 1, 2, 3, 4, 5 years after
vaccination.
Revaccination:
All of
chidren who had the DTH negative response 6 months after BCG vaccination, were
revaccinated with 0.1mg of BCG vaccine. The revaccination was realized two
times only. The DTH response was also observed after 1, 2, 3, 4 and 5 years
after BCG vaccination.
Results
After observating on 800 children from 0 to 15 years old (1993–1997), we obtained the following results:
After
five years of the first BCG vaccination, 49 – 70% of individuals had DTH
positive response.
Table 2. Percentage of DTH positive response after five years of the first BCG vaccination
|
Age |
n |
% DTH response positive |
||||
|
After |
After |
After |
After |
After |
||
|
0 – 1 |
100 |
100 |
85 |
75 |
60 |
49 |
|
> 1 – 5 |
100 |
90 |
85 |
75 |
65 |
56 |
|
> 5 – 10 |
100 |
100 |
89 |
70 |
65 |
57 |
|
> 10 -15 |
100 |
100 |
90 |
85 |
75 |
70 |
· 49 – 70% of children had DTH response positive.
After five
years of the second BCG vaccination, 60 - 63% of individuals had DTH positive response.
Table 3. Percentage of DTH positive response after five years of the second BCG vaccination
|
Age |
n |
% DTH response positive |
||||
|
After |
After |
After |
After |
After |
||
|
> 1 – 5 |
100 |
95 |
85 |
76 |
69 |
60 |
|
> 5 – 10 |
100 |
98 |
95 |
90 |
85 |
67 |
|
> 10 –15 |
100 |
95 |
80 |
75 |
65 |
63 |
* 60 - 63% of children had DTH response positive.
After five
years of the second BCG vaccination, 60% of individuals had DTH positive response.
Table 4. Percentage of DTH positive response after five years of the third BCG vaccination
|
Age |
n |
% DTH positive response |
||||
|
After |
After |
After |
After |
After |
||
|
5 – 15 |
100 |
95 |
83 |
70 |
65 |
60 |
* 60% of children had DTH positive response.
Thus, after five years of observation on 800 children who were vaccinated one, two and three times, we found that 60.25% of individuals had DTH positive response.
Table 5. Percentage of DTH positive response after five years of BCG vaccination
|
Age |
n |
% DTH positive response |
||||
|
After |
After |
After |
After |
After |
||
|
0 - 15 |
800 |
96.62 (773/800) |
86.50 (692/800) |
77.00 (616/800) |
68.62 (549/800) |
60.25 (482/800) |
* 60.25% of children had DTH positive response.
This result (60.25%) is:
lower than
the results in Cowall’s study (1949-1959) 98.58%; Sim (1949) in Qu’appelle
with French BCG vaccine (< 3 months)
80%; Dam (1990) in Brazil with Moreau vaccine (0-12yrs) 82-90% and Vandiviere (1973) in Canada with Canada
vaccine (< 20 yrs) 80%.
not different from the
results in Dam’s study (1990) in
higher than the results
of Dam (1990) in
The difference of the results may be due to:
BCG strain.
The ecology of different atypic Mycobacteria.
Ethnic immunity.
The sanitary, economical and social conditions
of different regions.
During 5 years of observation (1993-1997) on the DTH
response, we found that 60.25% of 800 individuals had the delayed type
hypersensitivity positive response after five years of BCG vaccination. This
result demonstrated the high efficacy of BCG vaccine produced by the Pasteur
Institute,
However, with the high annual risk of Mycobacterium tuberculosis infection (3.2%) and the high rate of tuberculosis in HIV patients (8%), a program of BCG revaccination against to tuberculosis should be suggested as soon as the immunity of vaccinated children decreases.