Abstract
Introduction: Pfizer-BioNTech Covid-19 vaccine is highly purified single-stranded messenger RNA (mRNA) produced using a cell-free in vitro transcription from the corresponding DNA templates indicated for preventing coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [1]. Olfactory hallucination is a condition in which a person perceives odors that aren't present. Some might notice the odor in just one nostril, while others have it in both [2]. Objective: The purpose of this review is to assess the risk of olfactory hallucinations from the Pfizer-BioNTech Covid-19 vaccine and, if necessary, make regulatory recommendations. Methods: The Signal Detection (SD) team at SFDA performed a signal review using the National Pharmacovigilance Center (NPC) database and World WHO database, VigiBase, with literature screening to retrieve all related information to assess the causality between olfactory hallucinations and Pfizer-BioNTech Covid-19 vaccine use. The search was conducted on January 4th, 2022. The disproportionality of the observed and the expected reporting rates for drug/adverse drug reaction pair was estimated using an information component (IC), a tool developed by WHO-UMC to measure the reporting ratio. Positive IC reflects higher statistical association, while negative values indicate less statistical association. Results: Local Cases: The SD team at SFDA has searched the NPC database for individual case safety reports (ICSR) reporting olfactory hallucinations in association with the Pfizer-BioNTech COVID-19 vaccine. The search resulted in one ISCR and, on the basis of WHO-UMC causality assessment criteria, olfactory hallucinations were considered probably associated with the vaccine. Global Cases: A search was conducted in the WHO database (Vigibase) to retrieve all reported cases using a signal detection tool (Vigilyze) [3]. The search yielded 59 ICSRs. The signal detection team applied the WHO-UMC causality assessment tool on cases with a completeness score of (0.8) and above (n = 13). 11 cases were found supportive of the association, with 10 being probable and one being possible. Literature: Late November 2021, a case report of a 57-year-old woman seeking medical care after complaining of "smelling smoke" after receiving her second dose of the vaccine was published [4]. Datamining: The results of (IC = 1.9) revealed a positive statistical association for the vaccine/ADR combination. Conclusion: The weighted cumulative evidence identified from local and global cases is sufficient to suggest a causal association between the Pfizer-BioNTech COVID-19 vaccine and olfactory hallucinations. While a more thorough review of safety data is needed to confirm the risk, health care professionals should be aware of the risk that could happen after vaccination.