[Study on a high coverage of measles vaccine while high incidence of measles disease still appeared in Shaanxi province].
OBJECTIVE
To analyze the affecting factors on the cause of measles and measles vaccine under the high coverage of measles vaccine in Shaanxi province.


METHODS
Age distribution and vaccination history on measles cases were studied. Throat swabs were obtained from measles cases. Measles virus was isolated from collected specimens with phenol-chloroform extraction method. Amplification was performed by RT-PCR in order to amplify 450 bp fragment of the -COOH side of N gene,and then the sequences of PCR products were detected to confirm the gene type of measles virus. Sera were obtained from patients who were in acute phase of measles disease,and antibody titer against measles vaccine strain and wild strain were determined by small amounts neutralization test.


RESULTS
Measles cases with the history of measles vaccination were accounted for 38.97% of the total numbers. The geometrical mean titer (GMT) (56.18) against S191 attenuated strain was significant higher than that of wild strain (26.90) among these measles patients with history of having received measles vaccination. The GMT (25.40) against S191 attenuated strain was similar to that of wild strain (27.86) among these measles patients with non-history of measles vaccination. The antibody negative rate against wild strain was 19.15% to these sera from patients with the history of measles vaccination and antibody potency against S191 strain was less than 16.


CONCLUSIONS
The appearance of higher measles incidence under the higher coverage of measles vaccine indicated that measles epidemic strain might degenerate as the result regarding the failure of the present measles vaccine in protecting the transmission of H1 wild strain.
Li
Ping
P
Shaanxi Provincial Center for Disease Control and Prevention, Xi' an 710054, China.
Si
Yuan
Y
Liu
Yi
Y
Guan
Rong-hui
RH
D017677:Age Distribution; D000914:Antibodies, Viral / Q000097:blood; D001483:Base Sequence; D002681:China / Q000453:epidemiology; D004196:Disease Outbreaks / Q000517:prevention & control*; D006801:Humans; D015994:Incidence; D008457:Measles / Q000453:epidemiology / Q000517:prevention & control*; D008458:Measles Vaccine / Q000008:administration & dosage*; D008459:Measles virus / Q000235:genetics* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D009500:Neutralization Tests
D000914:Antibodies, Viral; D008458:Measles Vaccine