Type 2 component of oral poliovirus vaccine is slated for global withdrawal through a switch from trivalent oral poliovirus vaccine (tOPV) to bivalent oral poliovirus vaccine (bOPV) for preventing paralytic polio caused by circulating vaccine-derived poliovirus type 2. We aimed to assess immunogenicity and safety profile of six vaccination schedules with different sequential doses of inactivated poliovirus vaccine (IPV), tOPV, or bOPV.

A randomized controlled trial was conducted in China in 2015. After informed consent was obtained from a parent or legally acceptable representative, healthy newborn babies were randomly allocated to one of six groups: cIPV-bOPV-bOPV, cIPV-tOPV-tOPV, cIPV-cIPV-bOPV, cIPV-cIPV-tOPV, cIPV-cIPV-cIPV, and tOPV-tOPV-tOPV. The key eligibility criteria were: full-term birth (37-42 weeks of gestation), birthweight ≥2·5 kg, no obvious medical disorders and no polio vaccination. Infants received following three doses sequentially with 4- 6 weeks interval after collecting blood sample: cIPV-bOPV-bOPV, cIPV-tOPV-tOPV, cIPV-cIPV-bOPV, cIPV-cIPV-tOPV, cIPV-cIPV-cIPV, and tOPV-tOPV-tOPV; and will be proactively followed up for observing adverse events after the first dose and 30 days after all doses. Antibodies of type 1, 2, and 3 poliovirus were tested 30 days after the third dose. The primary study objective was to investigate immunogenicity and safety profile of different vaccine schedules, evaluated by seroconversion, seroprotection and antibody titre against poliovirus types 1, 2, and 3 in the per-protocol population.

Inclusion Criteria:

• Eligible participants were healthy full-term (37-42 weeks) infants aged 60-90 days who weighed more than 2·5 kg at birth with no obvious medical disorders, no polio vaccination, no immunoglobulin vaccinated, no other attenuated vaccine immured in the past 14 days and no other inactivated vaccine immured.

Exclusion Criteria:

• Participants were excluded if meet one or more of following criteria: were or were at risk of immunodeficiency, severe allergic reaction, acute fever and infectious diseases, severe chronic diseases, family history of allergies, convulsions, seizures, encephalopathy and psychiatric diseases, oral steroids at least 14 consecutive days in the past month, axillary temperature equal or greater than 38·0°C in the past three days, diarrhea (defection frequency equal or greater than three times per day) in the past seven days, and participated in other drug clinical trials.