Abstract and Introduction
Abstract
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies decay but persist 6 months postvaccination; lower levels of neutralizing titers persist against Delta than wild-type virus. Of 227 vaccinated healthcare workers tested, only 2 experienced outpatient symptomatic breakthrough infections, despite 59/227 exhibiting serologic evidence of SARS-CoV-2 infection, defined as presence of nucleocapsid protein antibodies.
Introduction
Neutralizing antibodies (nAbs) and binding antibodies (bAbs) appear to be associated with protection against symptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and coronavirus disease (COVID-19).[1,2] Early assessments of the Pfizer-BioNTech (https://www.pfizer.com) BNT162b2 COVID-19 mRNA vaccine observed >95% effectiveness against predominantly Alpha infections,[3] but the potential effect of waning postvaccine neutralizing titers is an ongoing concern.[4]
Apparent increases in vaccine-breakthrough infections may result from waning antibody titers, increases in exposure risk, and reduced vaccine effectiveness against Delta and other variants. In mid-2021, Delta became the dominant virus type in the United States.[5] Delta appears to cause increased hospitalization rates and has increased transmissibility compared with Alpha and other pre-Delta variants (;[6] Bolze et al., unpub. data, https://doi.org/10.1101/2021.06.20.21259195). We report bAb and nAb levels as well as clinically overt and asymptomatic breakthrough infections that occurred among US healthcare workers in the Prospective Assessment of SARS-CoV-2 Seroconversion (PASS) study,[7] conducted during January–August 2021.
Emerging Infectious Diseases. 2022;28(4):828-832. © 2022 Centers for Disease Control and Prevention (CDC)
