IMPORTANCE Administration of a BNT162b2 booster dose (Pfizer-BioNTech) to fully vaccinated individuals aged 60 years and older was significantly associated with lower risk of SARS-CoV-2 infection and severe illness. Data are lacking on the effectiveness of booster doses for younger individuals and health care workers.OBJECTIVE To estimate the association of a BNT162b2 booster dose with SARS-CoV-2 infections among health care workers who were previously vaccinated with a 2-dose series of BNT162b2. DESIGN, SETTING, AND PARTICIPANTSThis was a prospective cohort study conducted at a tertiary medical center in Tel Aviv, Israel. The study cohort included 1928 immunocompetent health care workers who were previously vaccinated with a 2-dose series of BNT162b2, and had enrolled between August 8 and 19, 2021, with final follow-up reported through September 20, 2021. Screening for SARS-CoV-2 infection was performed every 14 days. Anti-spike protein receptor binding domain IgG titers were determined at baseline and 1 month after enrollment. Cox regression with time-dependent analysis was used to estimate hazard ratios of SARS-CoV-2 infection between booster-immunized status and 2-dose vaccinated (booster-nonimmunized) status.EXPOSURES Vaccination with a booster dose of BNT162b2 vaccine. MAIN OUTCOMES AND MEASURESThe primary outcome was SARS-CoV-2 infection, as confirmed by reverse transcriptase-polymerase chain reaction. RESULTS Among 1928 participants, the median age was 44 years (IQR, 36-52 years) and 1381 were women (71.6%). Participants completed the 2-dose vaccination series a median of 210 days (IQR, 205-213 days) before study enrollment. A total of 1650 participants (85.6%) received the booster dose. During a median follow-up of 39 days (IQR, 35-41 days), SARS-CoV-2 infection occurred in 44 participants (incidence rate, 60.2 per 100 000 person-days); 31 (70.5%) were symptomatic. Five SARS-CoV-2 infections occurred in booster-immunized participants and 39 in booster-nonimmunized participants (incidence rate, 12.8 vs 116 per 100 000 person-days, respectively). In a time-dependent Cox regression analysis, the adjusted hazard ratio of SARS-CoV-2 infection for booster-immunized vs booster-nonimmunized participants was 0.07 (95% CI, 0.02-0.20).CONCLUSIONS AND RELEVANCE Among health care workers at a single center in Israel who were previously vaccinated with a 2-dose series of BNT162b2, administration of a booster dose compared with not receiving one was associated with a significantly lower rate of SARS-CoV-2 infection over a median of 39 days of follow-up. Ongoing surveillance is required to assess durability of the findings.

e Carbapenems are considered the treatment of choice for Acinetobacter baumannii infections. Many facilities implement preventive measures toward only carbapenem-resistant A. baumannii (CRAB). However, the independent role of the carbapenem resistance determinant on patient outcomes remains controversial. In a 6-year analysis of adults with A. baumannii bloodstream infection (BSI), the outcomes of 149 CRAB isolates were compared to those of 91 patients with carbapenem-susceptible A. baumannii. In bivariable analyses, CRAB BSIs were significantly associated with worse outcomes and with a delay in the initiation of appropriate antimicrobial therapy (DAAT). However, in multivariable analyses, carbapenem resistance status was no longer associated with poor outcomes, while DAAT remained an independent predictor. The epidemiological significance of A. baumannii should not be determined by its resistance to carbapenems. Acinetobacter baumannii is one of the ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, A. baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens (1), which result in a variety of serious infectious clinical syndromes (2-4). Apart from a continuous increment in incidence, offending human strains have also become more resistant (5). The prevalence of the extensively drug-resistant (XDR) A. baumannii phenotype (6) has increased exponentially worldwide (5,7,8).Carbapenems are considered the agents of choice for treating A. baumannii infections, as long as the isolates are susceptible (4, 9, 10). Therefore, resistance to carbapenems frequently determines the epidemiological significance of the pathogen (2, 10). Many hospitals utilize infection control preventive measures (isolation precautions, cohorting, and screening for asymptomatic carriage), targeting only patients with carbapenem-resistant A. baumannii (CRAB) strains (11). However, both molecular epidemiology and clinical epidemiology investigations do not support these practices. Many of the mechanisms of resistance to carbapenems are chromosomally encoded (12). Therefore, it might be appropriate to target the prevention of patient-to-patient transmission of all A. baumannii isolates, since even susceptible organisms might become resistant after they are acquired by a new host. Moreover, controlled clinical data correlating resistance to carbapenems with worse patient outcomes were subjected to several biases, i.e., the majority of studies had low sample size, infection was not appropriately differentiated from colonization, and most studies did not control for time to initiation of appropriate antimicrobial therapy (13)(14)(15)(16)(17)(18)(19)(20)(21)(22). Delay in initiating appropriate antimicrobial therapy (DAAT) is the strongest modifiable predictor of worse outcomes among septic patients (23,24), and DAAT has frequently been reported in A. baumannii infections (25). Therefore, the aim of this study was to explore the independent role of the carbapenem resistance phenotype on the clinical outcomes of pat...

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