Study on the possibility of transmission of live hepatitis A vaccinees (H_2 strain) from vaccinees to nonvaccinees

Objective To determine whether H_2 strain vaccine virus could transmit vaccinee to non vaccinated contacts.Methods Under the present investigation subjects,were selected on volun tary bases from Zhejiang Academy of Medical Sciences a primary school in Hangzhou.The live atten uated hepatitis A (H_2 strain)vaccine used in this study was provided by Zhejiang Academy of Medical Sciences.The IgM antibody and the total antibody to hepatitis A virus were determined by two kinds of ELISA diagnostic kits,respectively.Hepatitis A cases were diagnosed according to the symptoms, signs relative to hepatitis,as well as the emergence of the IgM antibody to hepatitis A virus.Hepati- tis A antigen(HAAg)was determined by ELISA based on the double-sandwich principle.Results 31 stool samples from four persons collected after 8 to 30 days of inoculation were tested for the pres- ence of HAAg and the results were negative.After taking 8 samples from the above sample pool and inoculating into KMB17 cultivated cells through two passages,we found live HAV in three vaccine recipients after 8～21 days.None of the 24 nonvaccinees had seroconversion of the antibody to HAV after 10～11 months of close contacts with recipients.Five months after the vaccination an epidemic of HA caused by wild type of HAV occurred in Hangzhou.The anti-HAV conversion status monito- ring showed that among 50 students,15 vaccine recipients were positive of antibody to HAV.The re- maining 35 non vaccinations showed 30 negative and 5 positive in IgM antibody,which proved they had not been infected with vaccine virus before.Conclusion The inoculation of the live,attenuated HAV vaccine,although it shows shedding of very small amount of HAV (H_2-strain),it has not let to horizontal transmission of the virus.That seems to have resulted from its limited amount of the vi- rus excretion and its low ability of transmitting through oral infection.