Safety and Immunogenicity of BNT162b2 Coadministered With SIIV in Adults 18 Through 64 Years of Age

This study will assess the safety and immunogenicity of a fourth dose (booster) of BNT162b2 when coadministered with SIIV compared to separate administration of the vaccines when given 1 month apart (SIIV followed by BNT162b2), in participants who have received 3 prior doses of 30 µg BNT162b2, with the third dose being at least 90 days before Visit 1 (Day 1).

* Healthy adults 18 through 64 years of age will be randomized 1:1 to either the co-administration group, or the separate administration group
* The duration of the study for each participant will be approximately 2 months
* There are 3 scheduled study visits each about 1 month apart
* The study will be conducted in New Zealand and Australia.


Eligibility Criteria:
Inclusion Criteria:

1. Participants 18 through 64 years of age, inclusive, at the time of consent.
2. Are willing and able to comply with all scheduled visits, treatment plan, laboratory tests, lifestyle considerations, and other study procedures.
3. Adults determined by clinical assessment, including medical history and clinical judgment, to be eligible for the study, including adults with preexisting stable disease, defined as disease not requiring significant change in therapy in the previous 6 weeks or hospitalization for worsening disease within 12 weeks before receipt of study intervention.
4. Have received 3 prior doses of 30 µg BNT162b2, with the third dose being at least 90 days before Visit 1 (Day 1). Documented confirmation of prior BNT162b2 receipt must be obtained prior to randomization.
5. Capable of giving personal signed informed consent, which includes compliance with the requirements and restrictions listed in the ICD and in this protocol.

Exclusion Criteria:

1. Other medical or psychiatric condition, including recent (within the past year) or active suicidal ideation/behavior, or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study.
2. Allergy to egg proteins (egg or egg products) or chicken proteins.
3. History of Guillain-Barré syndrome.
4. History of severe adverse reaction associated with a vaccine and/or severe allergic reaction (eg, anaphylaxis) to any component of the study intervention(s).
5. A positive SARS-CoV-2 test result (either by NAAT or rapid antigen test) within 28 days of Visit 1 (Day 1).
6. Immunocompromised individuals with known or suspected immunodeficiency, as determined by history and/or laboratory/physical examination.
7. Bleeding diathesis or condition associated with prolonged bleeding that would, in the opinion of the investigator, contraindicate intramuscular injection.
8. Women who are pregnant or breastfeeding.
9. Vaccination with any influenza vaccine \<6 months before study intervention administration, or planned receipt of any licensed or investigational nonstudy influenza vaccine during study participation.
10. Individuals who receive treatment with radiotherapy or immunosuppressive therapy, including cytotoxic agents or systemic corticosteroids (if systemic corticosteroids are administered for ≥14 days at a dose of ≥20 mg/day of prednisone or equivalent), eg, for COPD, or planned receipt throughout the study. Inhaled/nebulized, intra-articular, intrabursal, or topical (skin or eyes) corticosteroids are permitted.
11. Receipt of blood/plasma products or immunoglobulin, from 60 days before study intervention administration or planned receipt throughout the study.
12. Receipt of any passive antibody therapy specific to COVID-19 from 90 days before study intervention administration or planned receipt throughout the study.
13. Prior receipt of any COVID-19 vaccine other than BNT162b2 or receipt of more than 3 prior doses of BNT162b2.
14. Participation in other studies involving study intervention within 28 days prior to study entry and/or during study participation.
15. Investigator site staff or Pfizer/BioNTech employees directly involved in the conduct of the study, site staff otherwise supervised by the investigator, and their respective family members.