Immunogenicity and SARS-CoV-2 Infection following the Fourth BNT162b2 Booster Dose among Health Care Workers.

We found that the fourth vaccine dose had a protective effect, but shorter than the third vaccine dose. Cutoff point of 955 AU/mL was recognized for protection from illness. The decision to vaccinate the population with a booster dose should consider other factors, including the spread of disease at the point, chronic comorbidities and age, especially during shortage of vaccine supply.