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Prevention of SARS-CoV-2 Infection

Last Updated: October 19, 2021

Summary Recommendations
Summary Recommendations
  • The COVID-19 Treatment Guidelines Panel (the Panel) recommends COVID-19 vaccination for everyone who is eligible according to the Advisory Committee on Immunization Practices (AI).
  • The Panel recommends using one of the following anti-SARS-CoV-2 monoclonal antibodies (listed alphabetically) as post-exposure prophylaxis (PEP) for people who are at high risk of progressing to severe COVID-19 if infected with SARS-CoV-2 AND who have the vaccination status AND exposure history outlined in the text below:
    • Bamlanivimab 700 mg plus etesevimab 1,400 mg administered as an intravenous (IV) infusion (BIII); or
    • Casirivimab 600 mg plus imdevimab 600 mg administered as subcutaneous injections (AI) or an IV infusion (BIII).
  • The Panel recommends against the use of hydroxychloroquine for SARS-CoV-2 PEP (AI).
  • The Panel recommends against the use of other drugs for SARS-CoV-2 PEP, except in a clinical trial (AIII).
  • The Panel recommends against the use of any drugs for SARS-CoV-2 pre-exposure prophylaxis (PrEP), except in a clinical trial (AIII).
Rating of Recommendations: A = Strong; B = Moderate; C = Optional
Rating of Evidence: I = One or more randomized trials without major limitations; IIa = Other randomized trials or subgroup analyses of randomized trials; IIb = Nonrandomized trials or observational cohort studies; III = Expert opinion

General Prevention Measures

Transmission of SARS-CoV-2 is thought to mainly occur through exposure to respiratory droplets transmitted to those within six feet of an infectious person. Less commonly, airborne transmission of small droplets and particles of SARS-CoV-2 to persons further than six feet away can occur; in rare cases, people passing through a room that was previously occupied by an infectious person may become infected. SARS-CoV-2 infection via airborne transmission of small particles tends to occur after prolonged exposure (i.e., >15 minutes) to an infectious person who is in an enclosed space with poor ventilation.1

The risk of SARS-CoV-2 transmission can be reduced by covering coughs and sneezes and maintaining a distance of at least six feet from others. When consistent distancing is not possible, face coverings may reduce the spread of infectious droplets from individuals with SARS-CoV-2 infection to others. Frequent handwashing also effectively reduces the risk of infection.2 Health care providers should follow the Centers for Disease Control and Prevention (CDC) recommendations for infection control and the appropriate use of personal protective equipment.3

Vaccination remains the most effective way to prevent SARS-CoV-2 infection. Anti-SARS-CoV-2 monoclonal antibodies (mAbs) may also be effective as post-exposure prophylaxis (PEP) for certain groups of people who are at risk of progression to serious COVID-19 and who have not been fully vaccinated or who are not expected to mount an adequate immune response to vaccines.

Vaccines

The COVID-19 Treatment Guidelines Panel (the Panel) recommends COVID-19 vaccination for everyone who is eligible for it according to the Advisory Committee on Immunization Practices (AI). Currently, two mRNA vaccines are available in the United States. The two-dose series of the BNT162b2 (Pfizer-BioNTech) vaccine was approved by the Food and Drug Administration (FDA) for individuals aged ≥16 years, but it can be administered to individuals aged ≥12 years to <16 years under an Emergency Use Authorization (EUA). The two-dose series of the mRNA-1273 (Moderna) vaccine has an EUA for individuals aged ≥18 years. The FDA also issued an EUA for a single-dose human adenovirus type 26 (Ad26) vectored vaccine, Ad26.COV2.S (Johnson & Johnson/Janssen), for those aged ≥18 years. Clinical trials that are evaluating the use of these vaccines in younger age groups and clinical trials for other COVID-19 vaccine candidates are currently ongoing.4

In large placebo-controlled trials, the mRNA-1273 and BNT162b2 vaccines were >90% efficacious for preventing symptomatic, laboratory-confirmed COVID-19 and >95% efficacious for preventing severe COVID-19 after participants completed a two-dose series. The single-dose Ad26.COV2.S vaccine was 66% efficacious in preventing moderate to critical laboratory-confirmed COVID-19.5-7 The available data on the COVID-19 vaccines that have received EUAs or FDA approval have demonstrated that these vaccines can markedly reduce the risk of infection, severe disease, hospitalization, and death. These vaccines have been shown to be effective against currently circulating SARS-CoV-2 variants,8 although emerging data suggest some decrease in effectiveness against the Delta variant.9 Surveillance to determine the long-term efficacy of these vaccines is ongoing.

Immunocompromised people who are vaccinated with an mRNA vaccine can have suboptimal antibody responses and may benefit from a third dose of the same vaccine.10-12 Currently, CDC recommends that people who are moderately to severely immunocompromised receive an additional dose of the same mRNA vaccine product at least 28 days after the second dose of either the BNT162b2 or mRNA-1273 vaccine.13 This includes people who have:

  • Been receiving active cancer treatment for tumors or cancers of the blood
  • Received an organ transplant and are taking immunosuppressive therapy
  • Received a stem cell transplant within the last 2 years or who are taking immunosuppressive therapy
  • Moderate or severe primary immunodeficiency (e.g., DiGeorge syndrome, Wiskott-Aldrich syndrome)
  • Advanced or untreated HIV infection. Advanced HIV is defined as people with CD4 T lymphocyte cell counts <200/mm3, a history of an AIDS-defining illness without immune reconstitution, or clinical manifestations of symptomatic HIV.
  • Active treatment with high-dose corticosteroids or other immunosuppressive drugs

There are currently insufficient data to determine whether recipients of the Ad26.COV2.S vaccine may benefit from an additional dose of the same vaccine.

COVID-19 Vaccine Booster

Data from recent studies suggest that the protection against SARS-CoV-2 infection provided by COVID-19 vaccination may decrease over time, and the vaccines may be less effective at protecting recipients against the Delta variant. Emerging evidence also shows that vaccine effectiveness against SARS-CoV-2 infection is decreasing over time among health care professionals and other frontline essential workers.14,15 A small clinical trial reported that a BNT162b2 booster dose increased the vaccine-induced immune response in participants who had finished their primary series 6 months earlier.16

According to CDC recommendations, the following groups should receive a booster shot of the BNT162b2 COVID-19 vaccine at least 6 months after completing their primary series (i.e., the first two doses of the BNT162b2 vaccine):17

  • People aged ≥65 years;
  • Residents in long-term care settings who are aged ≥18 years; and
  • People aged 50 to 64 years who have underlying medical conditions.18

CDC has also stated that the following groups may receive a booster shot of the BNT162b2 vaccine at least 6 months after completing their primary series, though clinicians should evaluate the benefits and risks of administering a booster shot to a given patient on a case-by-case basis:

  • People aged 18 to 49 years who have underlying medical conditions;18 and
  • People aged 18 to 64 years who are at increased risk for SARS-CoV-2 exposure and transmission because of their occupational or institutional setting.17

Adverse Reactions

Local and systemic adverse events are relatively common with these vaccines. Most of the adverse events that occurred during vaccine trials were mild or moderate in severity (i.e., they did not prevent vaccinated people from engaging in daily activities). There have been a few reports of severe allergic reactions following COVID-19 vaccination, including rare reports of patients who experienced anaphylaxis after receiving an mRNA vaccine.7,19

Reports have suggested that there is an increased risk of thrombosis with thrombocytopenia in adults who have received the Ad26.COV2.S vaccine.7 Most reports of this rare and serious condition have been in women aged 18 to 49 years.20 Similar reports from Europe describe thrombocytopenia and venous thrombosis in patients who received the ChAdOx1 nCoV-19 (Oxford/AstraZeneca) vaccine, which uses a chimpanzee adenoviral vector.21,22 The American Society of Hematology and the American Heart Association/American Stroke Association Stroke Council Leadership have published considerations that are relevant to the diagnosis and treatment of the type of thrombosis with thrombocytopenia that occurs in people who receive the Ad26.COV2.S vaccine. These considerations include information on administering a nonheparin anticoagulant and intravenous (IV) immunoglobulin to these patients.23,24 Given the rarity of this syndrome and the unique treatment required, consider consulting a hematologist when treating these patients.

Myocarditis and pericarditis are rarely reported in people who have received COVID-19 vaccines, and most of the cases that have been reported were very mild and self-limiting. These conditions have occurred most often in male adolescents and young adults and people who have received mRNA vaccines.25

Guillain-Barré syndrome (GBS), a rare neurologic disorder, has been reported in approximately 12 people per million people who received the Ad26.COV2.S vaccine. 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.25

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 Maternal Fetal Medicine are recommending 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 now or who may become pregnant in the future.4,26-31 The ACOG publication includes a guide to assist clinicians during conversations about COVID-19 vaccination with pregnant patients.32

Post-Exposure Prophylaxis

Anti-SARS-CoV-2 Monoclonal Antibodies

Vaccination remains the most effective way to prevent SARS-CoV-2 infection. However, despite widespread availability of COVID-19 vaccines, a number of individuals are either not fully vaccinated or cannot mount adequate responses to the vaccine. Some of these individuals, if infected, are at high risk of progressing to serious COVID-19. Based on the results of two large randomized controlled trials, the FDA expanded the EUA indication for the anti-SARS-CoV-2 mAbs bamlanivimab plus etesevimab and casirivimab plus imdevimab to allow these combinations to be used as PEP for selected individuals.33

Recommendations

The Panel recommends using one of the following anti-SARS-CoV-2 mAbs (listed alphabetically) as PEP for people who are at high risk for progressing to severe COVID-19 if infected with SARS-CoV-2 AND who have the vaccination status AND exposure history outlined in the text below.

  • Bamlanivimab 700 mg plus etesevimab 1,400 mg administered as an IV infusion (BIII); or
  • Casirivimab 600 mg plus imdevimab 600 mg administered as subcutaneous (SQ) injections (AI) or an IV infusion (BIII).

Vaccination Status:

  • Not fully vaccinated (defined as people who were never vaccinated, those who received the first dose of a two-dose series, or those who received the second dose of a two-dose series or a single-dose vaccine <2 weeks ago); or
  • Fully vaccinated, but not expected to mount an adequate immune response (e.g., those with immunocompromising conditions, including those who are taking immunosuppressive medications).

AND

Exposure History to SARS-CoV-2:

  • Had a recent exposure to an individual with SARS-CoV-2 infection that is consistent with CDC close contact criteria; or
  • At high risk of exposure to an individual with SARS-CoV-2 infection because of a recent occurrence of SARS-CoV-2 infection in other individuals in the same institutional setting (e.g., nursing homes, prisons).

The doses should be administered as soon as possible and preferably within 7 days of high-risk exposure (BIII). The patient should be observed for at least 1 hour after the injections or infusion.

It should be noted that even though the EUA calls for the combination of bamlanivimab 700 mg plus etesevimab 1,400 mg administered as a single IV infusion, the clinical trial that was used to support the EUA only studied bamlanivimab monotherapy at a single dose of 4,200 mg (see Anti-SARS-CoV-2 Monoclonal Antibodies).

The EUA for casirivimab plus imdevimab allows for repeat dosing of casirivimab 300 mg plus imdevimab 300 mg once every 4 weeks using SQ injections or an IV infusion for those who meet the EUA criteria for PEP and have ongoing exposures. However, there are no data from the COVID-19 Phase 3 Prevention Trial or other studies on the utility of repeat dosing for individuals who continue to have high-risk exposures. Therefore, the Panel finds that there is insufficient evidence to recommend either for or against repeat dosing every 4 weeks for those who received PEP and who continue to have high-risk exposures.

If there are shortages of anti-SARS-CoV-2 mAbs or logistical constraints (e.g., limited space, not enough staff who can administer therapy), it may be difficult to administer these agents to all eligible patients. In situations where it is necessary to triage eligible patients, the Panel suggests prioritizing the treatment of COVID-19 over PEP. For further guidance on prioritizing the use of these mAbs, see this statement from the Panel.

Clinical Trial Data for Bamlanivimab Monotherapy

BLAZE-2 is a randomized, double-blind, Phase 3 trial that enrolled residents and staff of 74 skilled nursing and assisted living facilities in the United States. Each facility had had at least one confirmed index case of SARS-CoV-2 infection, and the staff and residents had no known history of COVID-19.34 All participants provided both nasal and nasopharyngeal (NP) swabs for reverse transcription polymerase chain reaction (RT-PCR)-based diagnostic tests and blood for SARS-CoV-2 antibody testing. Nasal and NP swabs were obtained weekly for 57 days.

Participants who were found to be RT-PCR and antibody negative were considered the prevention population. Between August and November 2020, the study randomized 1,175 participants 1:1 to receive either bamlanivimab monotherapy at a dose of 4,200 mg or placebo by IV infusion. The prevention population included 484 participants who received bamlanivimab (323 staff and 161 residents) and 482 participants who received placebo (343 staff and 139 residents). The baseline characteristics of the staff and resident populations were very different; for example, the residents had a median age that was >30 years higher than the staff (76 years vs. 43 years) and had greater risks for disease progression.

In the overall prevention population, 114 participants (11.9%) experienced mild or worse COVID-19 by Day 57. There was a significantly lower incidence of mild or worse COVID-19 in the bamlanivimab arm than in the placebo arm (8.5% vs. 15.2%; OR 0.43; 95% CI, 0.28–0.68; P < 0.001), with an absolute risk difference of -6.6 percentage points (95% CI, -10.7 to -2.6). The difference was most significant in the resident population, where the incidence of mild or worse COVID-19 was 8.8% in the in bamlanivimab arm compared to 22.5% in the placebo arm (OR 0.20; 95% CI, 0.08–0.49; P < 0.001), with an absolute difference of -13.7 percentage points (95% CI, -21.9 to -5.4). In contrast, the difference between the bamlanivimab and placebo arms did not achieve statistical significance in the staff prevention population. Similar findings were observed for the secondary endpoint of the incidence of moderate or worse COVID-19.

In the prevention population, 198 participants (20.6%) had positive RT-PCR results within 4 weeks of randomization. The frequency of positive results was significantly lower in the bamlanivimab arm than in the placebo arm (17.9% vs. 23.3%; OR 0.66; 95% CI, 0.46–0.94; P = 0.02), with an absolute risk difference of -5.4 percentage points (95% CI, -10.5 to -0.3). The difference was significant for the resident prevention population but not the staff prevention population. An additional secondary endpoint in this study was mortality due to COVID-19; a total of four participants died, all of whom were residents who were randomized to receive placebo.

The overall safety population included 1,175 participants. Serious adverse events were reported in 3.7% of bamlanivimab recipients and 3.2% of placebo recipients. Any adverse events were reported in 20.1% of participants in the bamlanivimab arm and 18.9% of those in the placebo arm. The types of events were balanced across the study arms. Hypersensitivity reactions that occurred within 24 hours of study product infusion were reported in three participants (0.5%) in the bamlanivimab arm and none in the placebo arm.

Clinical Trial Data for Casirivimab Plus Imdevimab

Casirivimab plus imdevimab was evaluated as PEP in a randomized, double-blind, placebo-controlled Phase 3 trial that was conducted at 112 sites in the United States, Romania, and Moldova.35 The trial enrolled individuals aged ≥12 years who were exposed to a household contact (the index patient) who had a positive SARS-CoV-2 RT-PCR result from a NP swab specimen that was collected within the previous 96 hours. Study participants were asymptomatic, had a negative NP RT-PCR result for SARS-CoV-2, and intended to live with the index patient for the 28-day duration of follow-up.

Participants were randomized 1:1 to receive casirivimab 600 mg plus imdevimab 600 mg or placebo administered as four SQ injections (2.5 mL per injection) at different sites. NP swabs were collected weekly. The primary efficacy endpoint was the proportion of participants who developed symptomatic, RT-PCR-confirmed SARS-CoV-2 infection during the 28 days of follow-up. Additional key efficacy endpoints included asymptomatic infection and the quantity and duration of viral shedding detected by NP swabs.

The primary analysis included 1,505 participants (753 in the casirivimab plus imdevimab arm and 752 in the placebo arm) who had negative SARS-CoV-2 RT-PCR results at baseline and who were subsequently found to be serum SARS-CoV-2 antibody negative. The mean age was 42.9 years, 45.9% of participants were men, and 9.3% of participants were Black or African American and 40.5% were Hispanic/Latino. The protocol-specified risk factors for progression to severe COVID-19 were present in 30.5% of participants, with approximately 75% meeting the high-risk criteria in the revised EUA.

The use of casirivimab plus imdevimab resulted in a significant reduction in the risk of symptomatic SARS-CoV-2 infection when compared with placebo (81.4% risk reduction: 11 of 753 participants [1.5%] vs. 59 of 752 patients [7.8%]; OR 0.17; P < 0.001). This risk reduction was present throughout the follow-up period, starting from the first week and continuing through Week 4. Using both asymptomatic and symptomatic infections as an endpoint, the use of casirivimab plus imdevimab was associated with a significant reduction in risk compared to placebo (66.4% risk reduction; 36 of 753 participants [4.8%] vs. 107 of 752 participants [14.2%]; OR 0.31; 95% CI, 0.21–0.46; P < 0.0001). Among the subset of participants who were found to be seropositive at baseline (and were therefore excluded from the primary analysis), only a small number of participants reached the study endpoints, and there was no significant difference in the number who reached the endpoints between the casirivimab plus imdevimab arm (1 of 235 patients [0.4%]) and the placebo arm (5 of 222 participants [2.3%]; OR 0.19; 95% CI, 0.02–1.68; P = 0.14).

Hospitalizations were rare, with no hospitalized participants in the casirivimab plus imdevimab arm and four in the placebo arm. Some participants in the study received casirivimab plus imdevimab before they received their RT-PCR results; among these participants, those who eventually received positive RT-PCR results had a shorter duration of viral detection than the participants in the placebo arm (mean of 1.1 vs. 2.2 weeks). The frequencies of adverse events were similar between the two arms.

Chloroquine and Hydroxychloroquine

  • The Panel recommends against the use of hydroxychloroquine for SARS-CoV-2 PEP (AI).

Both chloroquine and hydroxychloroquine have in vitro activity against SARS-CoV and SARS-CoV-2.36,37 A small cohort study without a control group suggested that hydroxychloroquine might reduce the risk of SARS-CoV-2 transmission to close contacts.38 There have been several large trials to determine whether hydroxychloroquine can reduce the risk of infection after exposure to infected individuals. These studies used different dosing schedules and targeted different at-risk populations. In addition, some studies were unable to confirm infection using molecular or antigen tests. None of these studies demonstrated any evidence of efficacy for hydroxychloroquine, and all showed a higher risk of generally mild adverse events in those who received the drug.39-41

Other Drugs for PEP

  • The Panel recommends against the use of other drugs for SARS-CoV-2 PEP, except in a clinical trial (AIII).

A number of other agents (e.g., ivermectin, hyperimmune gamma globulin, convalescent plasma, interferons, tenofovir with or without emtricitabine, vitamin D) are currently being investigated for SARS-CoV-2 PEP. The latest clinical trials for SARS-CoV-2 PEP can be found at ClinicalTrials.gov.

High concentrations of ivermectin have been shown to inhibit SARS-CoV-2 replication in vitro.42,43 Population data indicated that country-wide, mass-use of prophylactic chemotherapy for parasitic infections, including the use of ivermectin, was associated with a lower incidence of COVID-19.44 At this time, few clinical trials have evaluated the safety and efficacy of using ivermectin for SARS-CoV-2 pre-exposure prophylaxis (PrEP) or PEP. Although several studies have reported potentially promising results, the findings are limited by the design of the studies, their small sample sizes, and the lack of details regarding the safety and efficacy of ivermectin.

In a descriptive, uncontrolled interventional study of 33 contacts of patients with laboratory-confirmed COVID-19, no cases of SARS-CoV-2 infection were identified within 21 days of initiating ivermectin for PEP.45 In a small case-control study in SARS-CoV-2-exposed health care workers, 186 participants who became infected were matched with 186 uninfected controls. Of those who received ivermectin after exposure to SARS-CoV-2, 38 were in the infected group and 77 were in the uninfected group, which led the investigators to conclude that ivermectin reduced the incidence of SARS-CoV-2 infection.46

Pre-Exposure Prophylaxis

  • The Panel recommends against the use of any drugs for SARS-CoV-2 PrEP, except in a clinical trial (AIII).

Rationale

At present, there is no known agent that is effective in preventing infection when administered before exposure to SARS-CoV-2 (i.e., as PrEP). Clinical trials are investigating several agents, including emtricitabine plus tenofovir alafenamide or tenofovir disoproxil fumarate, hydroxychloroquine, ivermectin, and supplements such as zinc, vitamin C, and vitamin D. Studies of anti-SARS-CoV-2 mAbs that target SARS-CoV-2 are also underway. Please check ClinicalTrials.gov for the latest information.

Hydroxychloroquine, given at different doses and durations, has been studied in randomized controlled trials to assess whether it could prevent SARS-CoV-2 infection in those at risk for being exposed to infected individuals, such as healthcare workers. One study reported no evidence of a benefit of hydroxychloroquine, and it was ultimately halted due to futility before it reached its target enrollment.47 In another hydroxychloroquine study, which also did not meet its target enrollment and was stopped early, the majority of the potential transmission events were not confirmed by virologic testing.48 Neither study demonstrated any evidence of a reduction in rate of acquiring infection. Both studies reported an increased frequency of mild adverse events in the treatment group.

References

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