is a neurologic disorder that causes muscle weakness and sometimes paralysis. Most people with GBS fully recover, but some have permanent nerve damage. Onset typically occurs about 2 weeks after vaccination. GBS has mostly been reported in men aged ≥50 years.11 CDC provides regular updates on selected adverse events of COVID-19 vaccines on its website. Vaccination in Pregnant or Lactating People Pregnant and lactating individuals were not included in the initial COVID-19 vaccine trials. However, CDC, the American College of Obstetricians and Gynecologists (ACOG), and the Society for MaternalDownloaded from https://www.covid19treatmentguidelines.nih.gov/ on 7/6/2022 COVID-19 Treatment Guidelines 25 Fetal Medicine recommend vaccination for pregnant and lactating people based on the accumulated safety and efficacy data on the use of these vaccines in pregnant people, as well as the increased risk of severe disease in pregnant individuals with COVID-19. These organizations also recommend vaccination for people who are trying to become pregnant or who may become pregnant in the future.12-17 The ACOG publication includes a guide for clinicians on counseling pregnant patients about COVID-19 vaccination.18 Pre-Exposure Prophylaxis Anti-SARS-CoV-2 Monoclonal Antibodies Vaccination remains the most effective way to prevent SARS-CoV-2 infection and should be considered the first line of prevention. However, some individuals cannot or may not mount an adequate protective response to COVID-19 vaccines. Others may not have been fully vaccinated because they have a history of severe adverse reactions to a COVID-19 vaccine or its components. Based on the results of PROVENT, a large randomized controlled trial conducted when the major circulating SARS-CoV-2 variants were Alpha (B.1.1.7), Beta (B.1.351), Delta (B.1.617.2), and Epsilon (B.1.429),19 the FDA issued an Emergency Use Authorization (EUA) for the anti-SARS-CoV-2 monoclonal antibodies (mAbs) tixagevimab plus cilgavimab (Evusheld). The EUA allows these mAbs to be used as pre-exposure prophylaxis (PrEP) for certain individuals who are at high risk of progressing to severe COVID-19 if they become infected with SARS-CoV-2.20 A modification in the fragment crystallizable (Fc) region gives these anti-SARS-CoV-2 mAbs prolonged half-lives, resulting in potential protection from SARS-CoV-2 infection for up to 6 months, depending on the variant. The dose used in the PROVENT trial was tixagevimab 150 mg plus cilgavimab 150 mg, which was the dose that was initially authorized by the FDA. However, in vitro data showed that the BA.1 and BA.1.1 subvariants of the Omicron (B.1.1.529) variant have decreased susceptibility to tixagevimab plus cilgavimab.20-23 Because of these findings, on February 24, 2022, the FDA revised the EUA to authorize tixagevimab 300 mg plus cilgavimab 300 mg as the dose for individuals who are receiving these antiSARS-CoV-2 mAbs for the first time.20 For patients who previously received a dose of tixagevimab 150 mg plus cilgavimab 150 mg, the FDA EUA states that a second dose should be given as soon as possible. The specific dose a patient should receive for their second round of tixagevimab plus cilgavimab depends on the amount of time that has passed since the initial dose (see below). The Omicron BA.2 subvariant has been shown to retain near-full susceptibility to tixagevimab plus cilgavimab in vitro, so the dosing recommendations for these mAbs may be further refined in the future.20,23,24 When prescribing tixagevimab plus cilgavimab for SARS-CoV-2 PrEP, clinicians should be aware of some important limitations: • Tixagevimab plus cilgavimab is authorized for use as PrEP in a population that was not wellrepresented in the PROVENT trial (i.e., a very small proportion of the participants were immunocompromised). • There are no clinical trial efficacy data on preventing symptomatic COVID-19 with the tixagevimab 300 mg plus cilgavimab 300 mg dose. The new dose is based on pharmacokinetic/ pharmacodynamic (PK/PD) modeling that suggests this dose may have in vivo activity against the Omicron BA.1 and BA.1.1 subvariants.25 • Substantial uncertainty in the PK/PD model remains. It is possible that even if the tixagevimab 300 mg plus cilgavimab 300 mg dose is active against the Omicron BA.1 and BA.1.1 subvariants, it would provide only a limited duration (≤3 months) of protection. Limited data inform the timing for repeat doses of tixagevimab plus cilgavimab after the initial dose, and repeat doses of tixagevimab 300 mg plus cilgavimab 300 mg are not included in the current EUA. Downloaded from 9 Treatment Guidelines 26 • The safety data on using tixagevimab 300 mg plus cilgavimab 300 mg primarily comes from TACKLE, a Phase 3 clinical trial that evaluated the use of tixagevimab plus cilgavimab for the treatment of patients with mild to moderate COVID-19.25 • The tixagevimab 150 mg plus cilgavimab 150 mg dose that was initially authorized by the FDA may not be sufficient to prevent cases of COVID-19 caused by the Omicron BA.1 and BA.1.1 subvariants. There are no clinical data and only limited PK/PD data to guide the administration of repeat doses of tixagevimab plus cilgavimab in those who were