No title
BACKGROUND: Long-term prospective data on antibody and T-cell responses beyond the third COVID-19 mRNA vaccine dose, particularly in relation to prior SARS-CoV-2 infections and breakthrough infections, remain limited.METHODS: Health care workers (HCWs) vaccinated with BNT162b2 were enrolled in January 2021. Blood samples were collected before and one month after each of four vaccine doses through
