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Anti-SARS-CoV-2 Monoclonal Antibodies

Last Updated: October 19, 2021

The SARS-CoV-2 genome encodes four major structural proteins: spike (S), envelope (E), membrane (M), and nucleocapsid (N), as well as nonstructural and accessory proteins. The spike protein is further divided into two subunits, S1 and S2, that mediate host cell attachment and invasion. Through its receptor-binding domain (RBD), S1 attaches to angiotensin-converting enzyme 2 (ACE2) on the host cell; this initiates a conformational change in S2 that results in virus-host cell membrane fusion and viral entry.1 Anti-SARS-CoV-2 monoclonal antibodies (mAbs) that target the spike protein have been shown to have a clinical benefit in treating SARS-CoV-2 infection (as discussed below). Some anti-SARS-CoV-2 mAbs have been found to be effective in preventing SARS-CoV-2 infection in household contacts of infected patients2 and during SARS-CoV-2 outbreaks in skilled nursing and assisted living facilities.3

Anti-SARS-CoV-2 Monoclonal Antibodies That Have Received Emergency Use Authorizations From the Food and Drug Administration

Currently, three anti-SARS-CoV-2 mAb products have received Emergency Use Authorizations (EUAs) from the Food and Drug Administration (FDA) for the treatment of mild to moderate COVID-19 in nonhospitalized patients with laboratory-confirmed SARS-CoV-2 infection who are at high risk for progressing to severe disease and/or hospitalization. The issuance of an EUA does not constitute FDA approval. These products are:

  • Bamlanivimab plus etesevimab: These are neutralizing mAbs that bind to different, but overlapping, epitopes in the spike protein RBD of SARS-CoV-2.
    • The distribution of bamlanivimab plus etesevimab was paused in the United States because both the Gamma (P.1) and Beta (B.1.351) variants have reduced susceptibility to bamlanivimab and etesevimab.4 However, distribution of the agents has been reinstated in states with low rates of these and other variants that have reduced susceptibility to bamlanivimab and etesevimab. Please refer to the FDA webpage Bamlanivimab and Etesevimab Authorized States, Territories, and U.S. Jurisdictions for the latest information on bamlanivimab plus etesevimab distribution.
  • Casirivimab plus imdevimab: These are recombinant human mAbs that bind to nonoverlapping epitopes of the spike protein RBD of SARS-CoV-2.
  • Sotrovimab: This mAb was originally identified in 2003 from a SARS-CoV survivor. It targets an epitope in the RBD of the spike protein that is conserved between SARS-CoV and SARS-CoV-2.

The FDA has expanded the EUAs for bamlanivimab plus etesevimab and casirivimab plus imdevimab to authorize their use as post-exposure prophylaxis (PEP) for certain individuals who are at high risk of acquiring SARS-CoV-2 infection and, if infected, are at high risk of progressing to serious illness. See Prevention of SARS-CoV-2 Infection and the FDA EUA fact sheets for bamlanivimab plus etesevimab and casirivimab plus imdevimab for more information.

Anti-SARS-CoV-2 Monoclonal Antibodies for the Treatment of COVID-19

The recommendations and discussion below pertain only to the use of the authorized anti-SARS-CoV-2 mAb products for the treatment of COVID-19. For recommendations and discussion regarding the use of mAb products as PEP, see Prevention of SARS-CoV-2 Infection.

Recommendations

  • The COVID-19 Treatment Guidelines Panel (the Panel) recommends using one of the following anti-SARS-CoV-2 mAb products (listed alphabetically and not in order of preference) to treat nonhospitalized patients with mild to moderate COVID-19 who are at high risk of clinical progression (see the EUA criteria for use of the products and the related discussion below):
    • Bamlanivimab 700 mg plus etesevimab 1,400 mg administered as an intravenous (IV) infusion in regions where the combined frequency of potentially resistant SARS-CoV-2 variants is low (see the FDA webpage Bamlanivimab and Etesevimab Authorized States, Territories, and U.S. Jurisdictions; or
    • Casirivimab 600 mg plus imdevimab 600 mg administered as an IV infusion or as subcutaneous (SQ) injections; or
    • Sotrovimab 500 mg administered as an IV infusion.
  • When using casirivimab plus imdevimab, the Panel recommends:
    • Casirivimab 600 mg plus imdevimab 600 mg administered as an IV infusion (AIIa)
    • If an IV infusion is not feasible or would cause a delay in treatment, casirivimab 600 mg plus imdevimab 600 mg can be administered as four SQ injections (2.5 mL per injection) (BIII).
  • When using anti-SARS-CoV-2 mAbs, treatment should be started as soon as possible after the patient receives a positive result on a SARS-CoV-2 antigen test or nucleic acid amplification test (NAAT) and within 10 days of symptom onset.
  • The use of anti-SARS-CoV-2 mAbs should be considered for patients with mild to moderate COVID-19 who are hospitalized for a reason other than COVID-19 if they otherwise meet the EUA criteria for outpatient treatment.
  • Anti-SARS-CoV-2 mAbs are not currently authorized for use in patients who are hospitalized with severe COVID-19; however, they may be available through expanded access programs for patients who either have not developed an antibody response to SARS-CoV-2 infection or are not expected to mount an effective immune response to infection.
  • For guidance on prioritizing the use of anti-SARS-CoV-2 mAbs for the treatment or prevention of SARS-CoV-2 infection when logistical or supply constraints limit their availability, see The Panel’s Updated Statement on the Prioritization of Anti-SARS-CoV-2 Monoclonal Antibodies.

Rationale

In randomized, placebo-controlled trials in nonhospitalized patients who had mild to moderate COVID-19 symptoms and certain risk factors for disease progression, the use of anti-SARS-CoV-2 mAb products reduced the risk of hospitalization and death (see Table 3a).5-7 It is worth noting that these studies were conducted before the widespread circulation of variants of concern (VOC). The potential impact of these variants and their susceptibility to different anti-SARS-CoV-2 mAbs is discussed below.

Bamlanivimab Plus Etesevimab

This anti-SARS-CoV-2 mAb combination has demonstrated a clinical benefit in people with mild to moderate COVID-19 who are at high risk for progression to severe disease and/or hospitalization (see Table 3a). The distribution of bamlanivimab plus etesevimab was paused in the United States because both the Gamma (P.1) and Beta (B.1.351) variants have reduced susceptibility to bamlanivimab and etesevimab.4 However, distribution of the product has been reinstated across the United States because the combined frequency of the Gamma and Beta variants is <5%. Casirivimab plus imdevimab and sotrovimab are expected to remain active against the Gamma and Beta variants.

The FDA provides a list of states, territories, and U.S. jurisdictions in which bamlanivimab plus etesevimab is currently authorized. The Centers for Disease Control and Prevention (CDC) COVID-19 Data Tracker website has the latest information on variant frequencies by region in the United States.

Casirivimab Plus Imdevimab

On June 3, 2021, the FDA updated the EUA for casirivimab plus imdevimab to reduce the authorized dosage for a single IV infusion from casirivimab 1,200 mg plus imdevimab 1,200 mg to casirivimab 600 mg plus imdevimab 600 mg.6 The update also authorized SQ injection of these lower doses of casirivimab and imdevimab if an IV infusion is not feasible or would delay treatment. SQ administration requires four injections (2.5 mL per injection) at four different sites (see the FDA EUA for details).

The recommendation for using the lower dose of casirivimab 600 mg plus imdevimab 600 mg IV is based on the Phase 3 results from the R10933-10987-COV-2067 study (ClinicalTrials.gov Identifier NCT04425629). This double-blind, placebo-controlled randomized trial in outpatients with mild to moderate COVID-19 evaluated different doses of casirivimab plus imdevimab. The modified full analysis set included participants aged ≥18 years who had a positive SARS-CoV-2 polymerase chain reaction result at randomization and who had one or more risk factors for progression to severe COVID-19. The results demonstrated a 2.2% absolute reduction and a 70% relative reduction in hospitalization or death with receipt of casirivimab 600 mg plus imdevimab 600 mg. These results are comparable to the those observed for IV infusions of casirivimab 1,200 mg plus imdevimab 1,200 mg, which demonstrated a 3.3% absolute reduction and a 71% relative reduction in hospitalization or death among patients who received this higher dose of casirivimab plus imdevimab.8 See Table 3a for additional details from the trial.

The recommendation for using SQ injections to administer casirivimab plus imdevimab is based on safety data from the Phase 1 R10933-10987-HV-2093 study (ClinicalTrials.gov Identifier NCT04519437). This double-blind, placebo-controlled randomized trial compared casirivimab plus imdevimab administered by SQ injection to placebo in healthy volunteers who did not have SARS-CoV-2 infection. Injection site reactions were observed in 12% of the 729 casirivimab plus imdevimab recipients and in 4% of the 240 placebo recipients. According to the FDA EUA, in a separate trial that evaluated casirivimab plus imdevimab in symptomatic participants, there were similar reductions in viral load in the participants in the IV and SQ arms of the trial.6 However, because the safety and efficacy data for casirivimab plus imdevimab administered by SQ injection are limited, this route of administration should only be used when IV infusion is not feasible or would lead to a delay in treatment (BIII).

Sotrovimab

The data that support the EUA for sotrovimab are from the Phase 3 COMET-ICE trial (ClinicalTrials.gov Identifier NCT04545060). The COMET-ICE trial included outpatients with mild to moderate COVID-19 who were at high risk for progression to severe disease and/or hospitalization. A total of 583 participants were randomized to receive sotrovimab 500 mg IV (n = 291) or placebo (n = 292). The primary endpoint was the proportion of participants who were hospitalized for ≥24 hours or who died from any cause by Day 29. Endpoint events occurred in 3 of 291 participants (1%) in the sotrovimab arm and 21 of 292 participants (7%) in the placebo arm (P = 0.002), resulting in a 6% absolute reduction and an 85% relative reduction in hospitalizations or death associated with sotrovimab.7

Criteria for Using Anti-SARS-CoV-2 Monoclonal Antibodies Under the Emergency Use Authorizations

The FDA EUAs for the anti-SARS-CoV-2 mAbs include a list of specific conditions that place patients at high risk for clinical progression. On May 14, 2021, the FDA revised the EUAs to broaden these criteria.5,6 Notable changes included lowering the body mass index (BMI) cutoff from ≥35 to >25 and adding other conditions and factors (e.g., pregnancy, race or ethnicity). Other than being aged ≥12 years, there are no longer any age criteria restricting the use of these agents in patients with the following conditions: sickle cell disease, neurodevelopmental disorders, medical-related technological dependence, asthma, cardiovascular disease, hypertension, and chronic lung disease

Recommendations

The strength of the evidence for using anti-SARS-CoV-2 mAbs varies depending on the medical conditions and other factors that place patients at high risk for progression to severe COVID-19 and/or hospitalization. The ratings for the recommendations for the use of anti-SARS-CoV-2 mAbs as treatment are based on the FDA EUA criteria for the following.

Medical Conditions or Other Factors That Were Represented in Patients in Clinical Trials That Evaluated Anti-SARS-CoV-2 Monoclonal Antibodies

  • Aged ≥65 years (AIIa)
  • Obesity (BMI >30) (AIIa)
  • Diabetes (AIIa)
  • Cardiovascular disease (including congenital heart disease) or hypertension (AIIa)
  • Chronic lung diseases (e.g., chronic obstructive pulmonary disease, moderate-to-severe asthma, interstitial lung disease, cystic fibrosis, pulmonary hypertension) (AIIa)

Other Conditions or Factors That Had Limited Representation in Patients in Clinical Trials but Are Considered Risk Factors for Progression to Severe COVID-19 by the Centers for Disease Control and Prevention

  • An immunocompromising condition or immunosuppressive treatment (AIII). Many experts strongly recommend therapy for patients with these conditions, despite their limited representation in clinical trials.
  • Being overweight (BMI 25–30) as the sole risk factor (BIII)
  • Chronic kidney disease (BIII)
  • Pregnancy (BIII)
  • Sickle cell disease (BIII)
  • Neurodevelopmental disorders (e.g., cerebral palsy) or other conditions that confer medical complexity (e.g., genetic or metabolic syndromes and severe congenital anomalies) (BIII)
  • Medical-related technological dependence (e.g., tracheostomy, gastrostomy, or positive pressure ventilation that is not related to COVID-19) (BIII)

It is important to note that the likelihood of developing severe COVID-19 increases when a person has multiple high-risk conditions or comorbidities.9-12 Medical conditions or other factors (e.g., race or ethnicity) not listed in the EUAs may also be associated with high risk for progression to severe COVID-19. The current EUAs state that the use of anti-SARS-CoV-2 mAbs may be considered for patients with high-risk conditions and factors that are not listed in the EUAs. For additional information on medical conditions and other factors that are associated with increased risk for progression to severe COVID-19, see the CDC webpage People With Certain Medical Conditions. The decision to use anti-SARS-CoV-2 mAbs for a patient should be based on an individualized assessment of risks and benefits.7

Some of the Panel’s recommendations for using anti-SARS-CoV-2 mAbs according to the updated EUA criteria are based on preliminary results from the clinical trials that have evaluated these products. The details on the study designs, methods, and follow-up periods for these trials are currently limited. When peer-reviewed data from the Phase 3 trials become publicly available, the Panel will review the results and update the recommendations for using anti-SARS-CoV-2 mAbs if necessary.

Using Anti-SARS-CoV-2 Monoclonal Antibodies in Patients Hospitalized for COVID-19

The FDA EUAs do not authorize the use of anti-SARS-CoV-2 mAbs for the following patients:

  • Those hospitalized for COVID-19; or
  • Those who require oxygen therapy due to COVID-19; or
  • Those who are on chronic oxygen therapy due to an underlying non-COVID-19-related comorbidity and who require an increase in oxygen flow rate from baseline because of COVID-19.

The FDA EUAs do permit the use of these agents in patients who are hospitalized for a diagnosis other than COVID-19, provided they have mild to moderate COVID-19 and are at high risk for progressing to severe disease.13-15

Anti-SARS-CoV-2 mAbs have been evaluated in hospitalized patients with severe COVID-19. A substudy of the ACTIV-3 trial randomized patients who were hospitalized for COVID-19 to receive bamlanivimab 7,000 mg or placebo, each in addition to remdesivir. On October 26, 2020, study enrollment was halted after a prespecified interim futility analysis indicated a lack of clinical benefit for bamlanivimab.16,17

There are now data that support the use of casirivimab 4,000 mg plus imdevimab 4,000 mg in hospitalized patients with COVID-19 who are seronegative for the anti-spike protein antibody. In the RECOVERY study, hospitalized patients with COVID-19 were randomized to receive standard of care with casirivimab 4,000 mg plus imdevimab 4,000 mg IV or standard of care alone. There was no difference in 28-day all-cause mortality between the casirivimab plus imdevimab arm and the standard of care arm; 944 of 4,839 patients (20%) in the casirivimab plus imdevimab arm died versus 1,026 of 4,946 patients (21%) in the standard of care arm (rate ratio 0.94; 95% CI, 0.86–1.03; P = 0.17). However, in the subgroup of patients who were seronegative for the anti-spike protein antibody, there was a significant reduction in 28-day all-cause mortality in the casirivimab plus imdevimab arm (396 of 1,633 casirivimab plus imdevimab recipients [24%] died vs. 451 of 1,520 standard of care recipients [30%]; rate ratio 0.80; 95% CI, 0.70–0.91; P = 0.001).18 This higher dose of casirivimab plus imdevimab is not available through the current EUA, and currently, casirivimab plus imdevimab is only authorized for use in nonhospitalized patients with COVID-19. In addition, rapid serology testing that can identify seronegative individuals in real time is currently not widely available.

Anti-SARS-CoV-2 mAbs may be available through expanded access programs for the treatment of immunocompromised patients who are hospitalized because of COVID-19. It is not yet known whether these mAb products provide clinical benefits in people with B-cell immunodeficiency or other immunodeficiencies.

SARS-CoV-2 Variants and Their Susceptibility to Anti-SARS-CoV-2 Monoclonal Antibodies

In laboratory studies, some SARS-CoV-2 variants that harbor certain mutations have markedly reduced susceptibility to a number of the authorized anti-SARS-CoV-2 mAbs.19 The clinical relevance of reduced in vitro susceptibility of select variants to anti-SARS-CoV-2 mAbs is under investigation.

Some of the key SARS-CoV-2 variants that have been identified are:

  • Alpha (B.1.1.7): This variant retains in vitro susceptibility to all the anti-SARS-CoV-2 mAbs that are currently available through EUAs.5,6
  • Beta (B.1.351): This variant includes the E484K and K417N mutations, which results in markedly reduced in vitro susceptibility to bamlanivimab and etesevimab.5 In vitro studies also suggest that the Beta (B.1.351) variant has markedly reduced susceptibility to casirivimab, although the combination of casirivimab and imdevimab appears to retain activity against the variant. Sotrovimab also appears to retain activity against the variant.6,7
  • Gamma (P.1): This variant includes the E484K and K417T mutations, which results in markedly reduced in vitro susceptibility to bamlanivimab and etesevimab.5,20,21 The Gamma (P.1) variant also has reduced susceptibility to casirivimab; however, the combination of casirivimab plus imdevimab appears to retain activity against the variant. Sotrovimab also appears to retain activity against the Gamma (P.1) variant.6,7
  • Delta (B.1.617.2, non-AY.1/AY.2): This is the predominant VOC circulating in the United States. This VOC retains in vitro susceptibility to all the anti-SARS-CoV-2 mAbs that are currently available through FDA EUAs.5,6
Table A. SARS-CoV-2 Variants and Susceptibility to Anti-SARS-CoV-2 Monoclonal Antibodies
Table A. SARS-CoV-2 Variants and Susceptibility to Anti-SARS-CoV-2 Monoclonal Antibodies

Ongoing population-based genomic surveillance of the types and proportions of circulating SARS-CoV-2 variants, as well as studies on the susceptibility of different variants to available anti-SARS-CoV-2 mAbs, will be important in defining the utility of specific mAbs in the future.

Clinical Trials

See Table 3a for information on the clinical trials that are evaluating the safety and efficacy of anti-SARS-CoV-2 mAbs in patients with COVID-19.

SARS-CoV-2 Vaccination

The CDC recommends that SARS-CoV-2 vaccination for people who have received anti-SARS-CoV-2 mAbs be deferred until ≥90 days after the therapy is completed. This is a precautionary measure, as the mAb treatment may interfere with vaccine-induced immune responses.22

For people who develop COVID-19 after SARS-CoV-2 vaccination, if there are no logistical or supply constraints limiting the availability of the authorized mAbs, prior vaccination should not affect decisions regarding the use and timing of mAb treatment.22 For guidance on the use of anti-SARS-CoV-2 mAbs when there are logistical or supply constraints, see the Panel’s updated statement on the prioritization of anti-SARS-CoV-2 mAbs.

Monitoring

The authorized anti-SARS-CoV-2 mAbs should be administered by IV infusion or SQ injections and should only be administered in health care settings by qualified health care providers who have immediate access to emergency medical services and medications that treat severe infusion-related reactions.

Patients should be monitored during the IV infusion or SQ injections and for at least 1 hour after the infusion or injections are completed.

Adverse Effects

Hypersensitivity, including anaphylaxis and infusion-related reactions, has been reported in patients who received anti-SARS-CoV-2 mAbs. Rash, diarrhea, nausea, dizziness, and pruritis have also been reported.6,7,14 Injection site reactions, including ecchymosis and erythema, were reported in clinical trial participants who received casirivimab plus imdevimab by SQ administration.6

Drug-Drug Interactions

Drug-drug interactions are unlikely between the authorized anti-SARS-CoV-2 mAbs and medications that are renally excreted or that are cytochrome P450 substrates, inhibitors, or inducers (see Table 3c).

Considerations in Pregnancy

The use of anti-SARS-CoV-2 mAbs can be considered for pregnant people with COVID-19, especially those who have additional risk factors for severe disease (see the EUA criteria for the use of these products above).

As immunoglobulin (Ig) G mAbs, the authorized anti-SARS-CoV-2 mAbs would be expected to cross the placenta. There are no pregnancy-specific data on the use of these mAbs; however, other IgG products have been safely used in pregnant people when their use is indicated. Therefore, authorized anti-SARS-CoV-2 mAbs should not be withheld in the setting of pregnancy. When possible, pregnant and lactating people should be included in clinical trials that are evaluating the use of anti-SARS-CoV-2 mAbs for the treatment and/or prevention of COVID-19.

Considerations in Children

Please see Special Considerations in Children for therapeutic recommendations for children.

Drug Availability

Bamlanivimab plus etesevimab, casirivimab plus imdevimab, and sotrovimab are available through FDA EUAs. The availability of bamlanivimab plus etesevimab was previously restricted in areas with an elevated combined frequency of variants that have markedly reduced in vitro susceptibility to these agents (e.g., the Gamma and Beta variants). The FDA provides updated information on the distribution of bamlanivimab plus etesevimab in the United States. Efforts should be made to ensure that communities most affected by COVID-19 have equitable access to these mAbs.

References

  1. Jiang S, Hillyer C, Du L. Neutralizing antibodies against SARS-CoV-2 and other human coronaviruses. Trends Immunol. 2020;41(5):355-359. Available at: https://www.ncbi.nlm.nih.gov/pubmed/32249063.
  2. O'Brien MP, Forleo-Neto E, Musser BJ, et al. Subcutaneous REGEN-COV antibody combination to prevent COVID-19. N Engl J Med. 2021;385(13):1184-1195. Available at: https://www.ncbi.nlm.nih.gov/pubmed/34347950.
  3. Cohen MS, Nirula A, Mulligan MJ, et al. Effect of bamlanivimab vs placebo on incidence of COVID-19 among residents and staff of skilled nursing and assisted living facilities: a randomized clinical trial. JAMA. 2021;326(1):46-55. Available at: https://www.ncbi.nlm.nih.gov/pubmed/34081073.
  4. Public Health Emergency. Pause in the distribution of bamlanivimab/etesevimab. 2021. Available at: https://www.phe.gov/emergency/events/COVID19/investigation-MCM/Bamlanivimab-etesevimab/Pages/bamlanivimab-etesevimab-distribution-pause.aspx. Accessed October 14, 2021.
  5. Food and Drug Administration. Fact sheet for healthcare providers: emergency use authorization (EUA) of bamlanivimab and etesevimab. 2021. Available at: https://www.fda.gov/media/145802/download.
  6. Food and Drug Administration. Fact sheet for healthcare providers: emergency use authorization (EUA) of REGEN-COV (casirivimab and imdevimab). 2021. Available at: https://www.fda.gov/media/145611/download.
  7. Food and Drug Administration. Fact sheet for healthcare providers: emergency use authorization (EUA) of sotrovimab. 2021, Available at: https://www.fda.gov/media/149534/download.
  8. Weinreich DM, Sivapalasingam S, Norton T, et al. REGEN-COV antibody combination and outcomes in outpatients with COVID-19. N Engl J Med. 2021;Published online ahead of print. Available at: https://www.ncbi.nlm.nih.gov/pubmed/34587383.
  9. Kim L, Garg S, O'Halloran A, et al. Risk factors for intensive care unit admission and in-hospital mortality among hospitalized adults identified through the U.S. coronavirus disease 2019 (COVID-19)-associated hospitalization surveillance network (COVID-NET). Clin Infect Dis. 2021;72(9):e206-e214. Available at: https://www.ncbi.nlm.nih.gov/pubmed/32674114.
  10. Guan WJ, Liang WH, Zhao Y, et al. Comorbidity and its impact on 1590 patients with COVID-19 in China: A Nationwide Analysis. Eur Respir J. 2020;55(5):2000547. Available at: https://www.ncbi.nlm.nih.gov/pubmed/32217650.
  11. Zhang Y, Luo W, Li Q, et al. Risk factors for death among the first 80,543 COVID-19 cases in China: relationships between age, underlying disease, case severity, and region. Clin Infect Dis. 2021;Published online ahead of print. Available at: https://www.ncbi.nlm.nih.gov/pubmed/34043784.
  12. Rosenthal N, Cao Z, Gundrum J, Sianis J, Safo S. Risk factors associated with in-hospital mortality in a US national sample of patients with COVID-19. JAMA Netw Open. 2020;3(12):e2029058. Available at: https://www.ncbi.nlm.nih.gov/pubmed/33301018.
  13. Food and Drug Administration. Frequently asked questions on the emergency use authorization of casirivimab + imdevimab. 2020. Available at: https://www.fda.gov/media/143894/download.
  14. Food and Drug Administration. Frequently asked questions on the emergency use authorization for bamlanivimab and etesevimab. 2021. Available at: https://www.fda.gov/media/145808/download.
  15. Food and Drug Administration. Frequently asked questions on the emergency use authorization of sotrovimab. 2021. Available at: https://www.fda.gov/media/149535/download
  16. National Institute of Allergy and Infectious Diseases. Statement—NIH-sponsored ACTIV-3 trial closes LY-CoV555 sub-study. 2020. Available at: https://www.niaid.nih.gov/news-events/statement-nih-sponsored-activ-3-trial-closes-ly-cov555-sub-study.
  17. Activ-Tico Ly- CoV555 Study Group, Lundgren JD, Grund B, et al. A neutralizing monoclonal antibody for hospitalized patients with COVID-19. N Engl J Med. 2021;384(10):905-914. Available at: https://www.ncbi.nlm.nih.gov/pubmed/33356051.
  18. RECOVERY Collaborative Group, Horby PW, Mafham M, et al. Casirivimab and imdevimab in patients admitted to hospital with COVID-19 (RECOVERY): a randomised, controlled, open-label, platform trial. medRxiv. 2021;Preprint. Available at: https://www.medrxiv.org/content/10.1101/2021.06.15.21258542v1.full.
  19. Centers for Disease Control and Prevention. SARS-CoV-2 variant classifications and definitions. 2021. Available at: https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/variant-surveillance/variant-info.html. Accessed April 5, 2021.
  20. Wang P, Liu L, Iketani S, et al. Increased resistance of SARS-CoV-2 variants B.I.315 and B.I.I.7 to antibody neutralization. bioRxiv. 2021;Preprint. Available at: https://www.biorxiv.org/content/10.1101/2021.01.25.428137v2.
  21. Wang P, Wang M, Yu J, et al. Increased resistance of SARS-CoV-2 variant P.1 to antibody neutralization. bioRxiv. 2021;Preprint. Available at: https://www.biorxiv.org/content/10.1101/2021.03.01.433466v1.
  22. Centers for Disease Control and Prevention. Interim clinical considerations for use of COVID-19 vaccines currently approved or authorized in the United States. 2021. Available at: https://www.cdc.gov/vaccines/covid-19/clinical-considerations/covid-19-vaccines-us.html. Accessed September 16, 2021.