Special Investigation for Booster Dose of Comirnaty in Children Ages 6 Months Though 4 Years

Primary outcomes

1. Proportion of Participants With Adverse Reaction (AR)

   Time frame: For 28 days after the booster (4th) dose

   An adverse event was defined as any untoward medical occurrence attributed to COMIRNATY intramuscular injection for 6 months to 4 years old (monovalent: Omicron XBB.1.5) in a participant who was vaccinated. The relatedness was assessed by the physician. Events for which a causal relationship with intramuscular injection could not be ruled out were handled as ARs.

2. Proportion of Participants With Serious Adverse Reaction (SAR)

   Time frame: For 28 days after the booster (4th) dose

   An SAR was defined as any AR resulting in any of the following outcomes or deemed significant for any other reason: death; life-threatening; hospitalization or prolongation of existing hospitalization; persistent or significant disability/malfunction; congenital anomaly/birth defect; or other medically important events.

3. Proportion of Participants With Reactogenicity (≥ Grade 1) in Those Who Are Younger Than 2 Years of Age

   Time frame: Within 7 days after the date of the booster (4th) dose

   Local reactions and systemic events recorded in the health observation diary collected by the physician from study participants were handled as reactogenicity events.

   They were aggregated for the vaccinated participants by age group and grade. The results were aggregated by age group for local reactions and systemic events of grade 1 or higher.

   If the participants were younger than 2 years of age on the date of the booster (4th) dose, the following reactogenicity events were aggregated. Local reactions: injection site tenderness, redness, and injection site swelling. Systemic events: pyrexia, decreased appetite, somnolence, and irritability. If the participants were 2 years or older on the date of the booster (4th) dose, the following reactogenicity events were aggregated. Local reactions: injection site pain, redness, and injection site swelling. Systemic events: pyrexia, vomiting, diarrhoea, headache, malaise, chills, myalgia, and arthralgia.

4. Proportion of Participants With Reactogenicity (≥ Grade 1) in Those Who Are Aged 2 Years or Older

   Time frame: Within 7 days after the date of the booster (4th) dose

   Local reactions and systemic events recorded in the health observation diary collected by the physician from study participants were handled as reactogenicity events.

   They were aggregated for the vaccinated participants by age group and grade. The results were aggregated by age group for local reactions and systemic events of grade 1 or higher.

   If the participants were younger than 2 years of age on the date of the booster (4th) dose, the following reactogenicity events were aggregated. Local reactions: injection site tenderness, redness, and injection site swelling. Systemic events: pyrexia, decreased appetite, somnolence, and irritability. If the participants were 2 years or older on the date of the booster (4th) dose, the following reactogenicity events were aggregated. Local reactions: injection site pain, redness, and injection site swelling. Systemic events: pyrexia, vomiting, diarrhoea, headache, malaise, chills, myalgia, and arthralgia.