Objective  To investigate adverse reactions to three sequential schedules of polio vaccination among small children.

  Methods  Totally 216 healthy infants of two month-old and above were recruited from November to December 2018 at 8 immunization clinics in Feixiang district, Handan city, Hebei province and randomly divided into three groups (72 infants in each group) for different sequential schedules of polio vaccinations at 2, 3, and 4 month-old: group A (administered sequentially with inactivated poliovirus vaccine IPV, bivalent oral poliovirus vaccine of types I and III bOPV, and bOPV), group B (with IPV, IPV and bOPV), and group C (with three doses of IPV sequentially). Information on suspected adverse events following immunization (AEFI) among the vaccines were collected through 30 minutes observation after the inoculation, telephone or household interview at 1, 3, 7, 15, 30 days after the vaccination. The observed adverse reactions were classified according to the National Surveillance Plan for Suspected Adverse Events Following Immunization and the incidence rates of AEFI were compared among the three vaccination groups.

  Results  A Totally 16 cases of AEFI were reported, with an overall AEFI reporting rate of 2.52/100 doses. The reported number (incidence rate/100doses) of AEFI in the infants of groups A, B, and C were 5 (2.23), 2 (0.97), and 9 (4.41), respectively. There were no statistically significant differences in the reported AEFI rates between group A and group B and between group A and group C (χ² = 1.079, 1.603, P > 0.05); but the reported rate of the group B was significantly lower than that of group C (χ² = 4.683, P < 0.05); there was also no significant difference between the reported rate of the male infants (4 cases, 1.57/100 doses) and that of the female infants (12 cases, 3.16/100 doses) (χ² = 1.569, P > 0.05) . All the reported AEFI were febrile reactions, including 1 case of low-grade fever (0.16/100 doses), 11 cases of moderate fever (1.73/100 doses), and 4 cases of high fever (0.63/100 doses) and no rare serious adverse reactions was observed among the infants. All the reported AEFI occurred after the inoculations of first dose (13 cases, 6.02/100 doses) and second dose (3 cases, 1.43/100 doses) of vaccine, and the incidence rate of AEFI for the first dose vaccination was significntly higher than that for the second dose vaccination (χ² = 6.206, P < 0.05). All the 16 cases of AEFI occurred within 15 – 30 days after the vaccinations and recovered after symptomatic treatment.

  Conclusion  The three sequential schedules of IPV and bOPV vaccination are safe among 2 – 4 month-old infants and the reported incidence rate of AEFI is relatively low for the schedule of two sequential doses of IPV followed by one dose bOPV vaccination.