Preliminary Results from HERO-together: A Post-emergency Use Authorization Observational Cohort Study to Evaluate the Safety of the Pfizer-BioNTech COVID-19 Vaccine in US Healthcare Workers and Community Members

Background: In December 2020, Pfizer-BioNTech received emergency use authorization (EUA) for a vaccine to prevent COVID-19 in individuals 16 years of age and older. Post-authorization safety surveillance enables early insights into the real-world safety profile of vaccination. Preliminary findings from one of the first US-based COVID-19 observational studies on post-vaccine outcomes are presented below.

Objectives: To estimate incidence rates of adverse events of special interest (AESIs) and other clinically significant events among recipients of a COVID-19 vaccine.

Methods: HERO-Together is a prospective observational cohort study of healthcare workers, their families, and members of the community. Participants self-enroll up to 60 days following their first vaccine dose using a participant-facing web portal. Data on COVID-19 vaccination, demographics, medical history, non-routine medical care (including hospitalization) and AESI occurrence are collected via participant self-report at regular intervals. Medical records are collected and adjudicated to confirm participant-reported safety events. The primary analysis safety population (PASP) included participants who enrolled within 10 days of receiving their first dose of the Pfizer-BioNTech COVID-19 vaccine. Incidence proportions were calculated for all AESIs.

Results: Of the n=20,660 consented participants enrolled from 17 December 2020 through 23 September 2021, n=9,410 were included in the PASP and n=11,250 were not included in the primary analysis safety population (CNPASP). Baseline demographics, comorbidities, study withdrawals, medical history, and medication use were similar between these populations. The PASP was primarily white (65.3%), female (67.9%), and not Hispanic (74.1%). The incidence proportion of reported hospitalizations was low for the PASP (0.2% of participants). The most common adjudicated safety events in the PASP included arthritis/arthralgia (0.09%) and non-anaphylactic allergic reaction (0.04%), both non-hospitalized. Similar patterns were observed in the CNPASP.

Conclusions: In this prospective post-vaccine safety study, the frequencies of adjudicated AESIs, including hospitalizations, after receiving the Pfizer-BioNTech COVID-19 vaccine were low and most commonly included arthritis/arthralgia and non-severe allergic reaction. Clinical adjudication of events and participant follow-up is ongoing.