Introduction: Persistent silent circulation of wild type 1 poliovirus (WPV1) introduced into southern Israel in 2013 triggered two rounds of administration of bOPV in 4m-10y old children at the transmission epicenter and one round in all other regions of Israel in Aug-Nov 2013.
Aim: To determine the time course of excretion of Sabin strains after administration of bOPV (Sabin 1 and 3) by the vaccinated children who had previously received only IPV.
Methods: 50-100 convenient stool samples were collected weekly between 1-9-2013 and 28-1-2014. RNA was extracted from the stool samples by the King Fisher and was analyzed by Real Time qRT- PCR for Sabin-1 and Sabin-3. The samples were divided into 3 groups based on the child bOPV vaccination history: G2- two doses (n=658); G1- one dose (n=693); G0- no dose (n=63). The percent of excretors was analysed with respect to the interval in weeks between stool collection and last vaccine administration.
Results: The percentage of Sabin-positive stools decreased linearly for 8 weeks for G1 and 4 weeks for G2, and then tailed at <10% for 17 weeks post vaccination for G1 or 12 weeks for G2. Altogether 6/63 (10%), 108/693(15%) and 114/658(17.3%) were Sabin positive for G0, G1, and G2, respectively.
Conclusion: A large proportion of children excreted Sabin strains for prolonged periods post bOPV vaccination: 6 weeks after 1 dose and 3 weeks after 2 doses. A secondary exposure to Sabin strains may explain the unexpected Sabin-positive G0 stools and the long "tails" for G1 and G2.
