Data extraction
We extracted as many relevant variables as possible from the information
provided (age, date, etc.) and according to the main stratification
variable, author, country, data source, age range, study timeframe,
baseline population group, outcome (symptoms after vaccination, severity
symptoms), total sample, others. We additionally included another
category of the length of stay in the hospital or ICU. We retrieved data
on the age who are confirmed vaccinated by BioNTech-Pfizer COVID-19,
confirmed symptoms after vaccination, and length of stay in hospitals or
ICU from publicly available data. All studies included in this review
were published in the United States of America (USA).