Formed a large lump, under my arms; Underarms started to hurt; Started feeling chills; This spontaneous case was received on 26-Oct-2023 from other non healthcare professional (consumer) via Pfizer, Inc. (reference number US-PFIZER INC-PV202300168237) and concerned a patient of unreported age and gender.  The patient's concurrent conditions included asthma. The patient's concomitant medication included albuterol for asthma. The patient's historical vaccines included an unspecified number of COVID-19 booster vaccines received in Oct-2022, after which the patient experienced chills.  On 07-Oct-2023, the patient was vaccinated with Flucelvax Quadrivalent (influenza vaccine inact split 4v; dose: 0.15 ml; route of administration, anatomical location, and indication: not reported). The batch number reported was 944463 (reported batch number was identified by Seqirus to be correct batch number). The expiry date reported was 30-Jun-2024.  On the same day, the patient was vaccinated with non-company co-suspect Comirnaty vaccine (tozinameran; dose: 0.3 ml; anatomical location: left arm; route of administration: intramuscular; and indication: 'I don't want to catch COVID. I want to prevent it as much as I can', as reported). The batch number reported was HF9275.  On the same day, later in the day, as reported, after receiving Flucelvax and Comirnaty vaccines, the patient started feeling, where about chills, and that was all that the patient was expecting. Later in the day, as reported, the patient's underarms started to hurt, and it formed a large lump under arms. The patient used warm compresses and took ibuprofen and Tylenol (paracetamol).  At the time of the initial reporting, the patient was recovering from the event of 'axillary lump'. The patient reported the lump was going down, but it was still there.  The outcome of the events 'axillary pain' and chills was unknown.  The reporter did not provide a causality assessment.  Company comment: A patient of unreported age and gender was vaccinated with Flucelvax Quadrivalent and non-company co-suspect Comirnaty vaccine, on the same date. Reportedly, on the same date, patient started to feel chills, and later complained of axillary pain. In addition, patient noticed that was formed a large mass in the underarms. Relevant laboratory and diagnostic findings were not provided. Causality is confounded by concurrently administered non-company co-suspect Comirnaty vaccine. Despite confounding by co-suspect vaccine, causal role of the suspect vaccine cannot be excluded due to suggestive temporal relationship and biological plausibility, therefore is assessed as possibly related for all reported events (chills, axillary pain and axillary mass).; Sender's Comments: A patient of unreported age and gender was vaccinated with Flucelvax Quadrivalent and non-company co-suspect Comirnaty vaccine, on the same date. Reportedly, on the same date, patient started to feel chills, and later complained of axillary pain. In addition, patient noticed that was formed a large mass in the underarms. Relevant laboratory and diagnostic findings were not provided. Causality is confounded by concurrently administered non-company co-suspect Comirnaty vaccine. Despite confounding by co-suspect vaccine, causal role of the suspect vaccine cannot be excluded due to suggestive temporal relationship and biological plausibility, therefore is assessed as possibly related for all reported events (chills, axillary pain and axillary mass).