[A three-year follow-up study on sera specific antibody in severe acute respiratory syndrome cases after the onset of illness].

OBJECTIVE: To study the variation of specific antibody among convalescent of severe acute respiratory syndrome (SARS) patients through a three-year program. METHODS: Sera samples were collected from SARS cases in the 5th, 20th and 35th month after onset of the illness. The SARS-CoV specific antibody was detected for all of them by ELISA and neutralized test simultaneously. The titer of neutralizing antibodies was calculated using Reed-Muench method, and the comparison between different time groups was analyzed regarding the variance of data on repeated measures after logarithm conversion. RESULTS: 13, 17 and 13 sera samples were collected in the 5th, 20th and 35th month after onset. Results showed that despite the fact that the positive rates of ELISA antibody were 100%, 82.4% and 84.6% respectively,the neutralizing antibody was still positive for all the samples. The average neutralizing antibody titers were 1:43 (1:16-1:203), 1:36 (1:17-1:59) and 1:21 (1:10-1:39) on the 5th, 20th and 35th month after onset, and the differences were statistically significant (F = 60.419, P < 0.001). On the 35th month after the onset, 30.8% (4/13) of the patients were still having the neutralizing antibody level of above 1:36, but the neutralizing antibody level in another 30.8% (4/13) of the patients had decreased to as low as 1:10, when the cut-off level was set as 1:8. CONCLUSION: Results of the study indicated that the neutralizing antibody of SARS cases could last for at least three years, but the sera specific antibody in SARS cases decreased gradually when time went by. However, neutralizing antibody in some of the cases decreased to a lower level on the 35th month. Further follow-up study was worthwhile to observe the long-lasting profile of antibody existence on SARS cases.

[Study on a 10-year protective effects of vaccination against hemorrhagic fever with renal syndrome].

OBJECTIVE: To evaluate the epidemiological and serological efficacy after 10 years of vaccination against hemorrhagic fever with renal syndrome (HFRS) vaccines in Zhejiang province. METHODS: One county was randomly chosen as the research unit with all the healthy people between 16 and 60 years old were equally divided into study and control groups. The study group was vaccinated. Immunofluorescent antibody assay was used to test specific IgG antibody and Mcro-CPE method was used to test the titer of neutralizing antibody. RESULTS: Two weeks after the full-course immunization, the seroconversion rate became 100% (67/67, with 95% CI as 96.3%-100%) by immunofluorescent antibody test (IgG) and 44.4% (8/18 with 95% CI as 22.0%-69.0%) by neutralization test with GMT titers as 72.1 and 4.6 respectively. Booster immunization was provided one year later. Time span as two weeks prior to, one year, one and half years, two years, three years and five years after booster immunization, the rates of seroconversion on immunofluorescent antibody using IFAT method, were 28.6%, 83.3%, 75.0%, 53.1%, 22.6%, 10.0% and 55.0% respectively, and rates of seroconversion of neutralizing antibody by Mcro-CPE method were 14.8%, 55.6%, 35.0%, 31.3%, 26.0%, 10.0% and 50.0% respectively. Nine years after the reinforcement, the rates of seroconversion of immunofluorescent antibody by IFAT method was only 7.1%. The vaccinated group had no patient seen but the control group appeared 34 patients including 3 deaths. According to the ten-year observation, the vaccine seemed effective with the protection rate in population reached 100%. CONCLUSION: HFRS vaccine was effective on epidemiological, social and economical efficacy.