Prevention and Prophylaxis of SARS-CoV-2 Infection
Last Updated: July 8, 2021
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 from an infectious person to others within six feet of the 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 further 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 appropriate use of personal protective equipment (PPE).3 Another important way to prevent SARS-CoV-2 infection is through vaccination.
Currently, no SARS-CoV-2 vaccine has been approved by the Food and Drug Administration (FDA). In December 2020, the FDA issued Emergency Use Authorizations (EUAs) for two mRNA vaccines, BNT162b2 (Pfizer-BioNTech)4 and mRNA-1273 (Moderna).5 In February 2021, the FDA issued an EUA for a human adenovirus type 26 (Ad26) vectored vaccine, Ad26.COV2.S (Johnson & Johnson/Janssen).6 BNT162b2 can be administered to individuals aged ≥12 years, whereas mRNA-1273 and Ad26.COV2.S can be given to individuals aged ≥18 years. Clinical trials for these vaccines in younger age groups and clinical trials for other SARS-CoV-2 vaccine candidates are currently ongoing.7
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. Cases of COVID-19 were confirmed by the presence of symptoms and a positive result on a SARS-CoV-2 nucleic acid amplification test (NAAT).6,8,9 Newly emerging data indicate that the SARS-CoV-2 vaccines authorized for use in the United States prevent asymptomatic infection, transmission, and infection by currently circulating or emergent variants of SARS-CoV-2.10
Local and systemic adverse events are relatively common with these vaccines, and they are especially common after the second dose of a SARS-CoV-2 mRNA vaccine. Most adverse events that occurred in 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 SARS-CoV-2 vaccination, including rare reports of patients who experienced anaphylaxis after receiving a SARS-CoV-2 mRNA vaccine.6,11
Reports of adverse events following the use of the Ad26.COV2.S vaccine under the FDA EUA suggest that there is an increased risk of thrombosis with thrombocytopenia in adults.6 As of June 7, 2021, thrombosis with thrombocytopenia has been reported to occur at a rate of approximately three people per million people who received this vaccine in the United States.12 Nearly all reports of this serious condition have been in vaccinated women aged 18 to 49 years. This adverse event is even more rare among women aged ≥50 years and men of all ages.13 Onset of symptoms typically occurs during the first 3 weeks after vaccination.14-16 Thrombosis can occur in atypical locations, including the cerebral and abdominal veins; in addition, lower extremity thrombosis and pulmonary emboli may occur. Similar reports from Europe describe thrombocytopenia and venous thrombosis in patients who received the ChAdOx1 nCoV-19 vaccine (Oxford/AstraZeneca), which uses a chimpanzee adenoviral vector. The incidence of cerebral vein thrombosis after vaccination with the ChAdOx1 nCoV-19 vaccine is higher than expected compared to the general population, but lower than the incidence reported for people with COVID-19 (42.8 occurrences per million people).17,18 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 immunoglobulin to these patients.19,20 Given the rarity of the syndrome and the unique treatment required, consider consulting a hematologist when treating these patients. Vaccine safety data continue to be collected.
Pregnant and lactating individuals were not included in the initial vaccine trials. A study that used data from three vaccine safety reporting systems in the United States reported that the frequency of adverse events among 35,691 vaccine recipients who identified as pregnant was similar to the frequency observed among nonpregnant patients (see Special Considerations in Pregnancy).7 The American College of Obstetricians and Gynecologists has published practice guidance on the use of the SARS-CoV-2 mRNA vaccines in pregnant and lactating people, including a guide to assist clinicians during risk and benefit conversations with pregnant patients.21
CDC sets the adult and childhood immunization schedules for the United States based on recommendations from the Advisory Committee on Immunization Practices (ACIP). The COVID-19 Treatment Guidelines Panel (the Panel) recommends that health care providers follow recommendations from ACIP when using SARS-CoV-2 vaccines (AI). ACIP considers disease epidemiology, burden of disease, vaccine efficacy and effectiveness, vaccine safety, the quality of the available evidence, and potential vaccination implementation issues. ACIP also sets priorities regarding who receives vaccines in the event of a shortage. ACIP’s COVID-19 vaccine recommendations are reviewed by CDC’s Director and, if adopted, are published as official CDC recommendations in the Morbidity and Mortality Weekly Report.22
CDC has provided guidance on resuming activities without wearing a mask or physically distancing for people who are fully vaccinated (people are considered fully vaccinated 2 weeks after completing a two-dose vaccine series or receiving a single-dose vaccine, such as the Ad26.COV2.S vaccine). This guidance does not apply in places where masks are required by federal, state, local, tribal, or territorial laws, rules, and regulations, and individual businesses or workplaces may have their own mask requirements.23
- The Panel recommends against the use of any drugs for SARS-CoV-2 pre-exposure prophylaxis (PrEP), except in a clinical trial (AIII).
At present, there is no known agent that can be administered before exposure to SARS-CoV-2 (i.e., as PrEP) to prevent infection. 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 monoclonal antibodies that target SARS-CoV-2 are in development. Please check ClinicalTrials.gov for the latest information.
Clinical Trial Data
Randomized Controlled Trial of Hydroxychloroquine for SARS-CoV-2 Pre-Exposure Prophylaxis Among Health Care Workers
This double-blind, placebo-controlled randomized trial was designed to determine whether hydroxychloroquine 600 mg per day reduced the frequency of SARS-CoV-2 infection over an 8-week period in hospital-based health care workers. The primary outcome was incidence of SARS-CoV-2 infection (as determined by reverse transcriptase polymerase chain reaction [RT-PCR] assay of nasopharyngeal swabs collected at 4 and 8 weeks) or the occurrence of COVID-19 symptoms.24Study Population
- Participants included health care workers at two Philadelphia hospitals who worked ≥20 hours per week in a hospital-based unit, had no known history of SARS-CoV-2 infection, and had no COVID-19-like symptoms in the 2 weeks before enrollment. The study enrolled workers in the emergency department (ED) and in dedicated COVID-19 treatment units.
- The study excluded individuals who were allergic to hydroxychloroquine and those with glucose-6-phosphate dehydrogenase deficiency, retinal disease, or substantial cardiac disease.
- The study was based on an assumed 10% infection rate for the planned inclusion of 100 participants per arm.
- Between April 9 and July 14, 2020, community SARS-CoV-2 infection rates declined. At the time of the second interim analysis (when 125 of 132 participants who provided consent were evaluable for the primary endpoint), the Data Safety Monitoring Board recommended early termination of the study for futility.
- Four participants in each arm developed SARS-CoV-2 infection (positivity rate of 6.3% in the hydroxychloroquine arm vs. 6.6% in the placebo arm; P > 0.99). Across both arms, six participants developed symptoms of COVID-19, but none required hospitalization.
- Serologic testing for antispike protein immunoglobulin (Ig) M, IgG, and nucleocapsid protein IgG demonstrated more positive results among participants in the hydroxychloroquine arm (four participants [7.4%]) than in the placebo arm (two participants [3.7%]), although the difference was not statistically significant (P = 0.40).
- Mild adverse events were more common among participants in the hydroxychloroquine arm (45%) than in the placebo arm (26%; P = 0.04). The greatest difference was the increased frequency of mild diarrhea in the hydroxychloroquine arm.
- The rates of treatment discontinuation were similar in the hydroxychloroquine arm (19%) and the placebo arm (16%).
- There were no cardiac events in either arm, as well as no significant difference in the median frequency of changes in QTc between the study arms (P = 0.98).
- The study was stopped early.
- Due to the low SARS-CoV-2 infection rate among the participants, the study was underpowered to detect a prophylactic benefit of hydroxychloroquine.
- The study population was mostly young, healthy health care workers; therefore, whether the study findings are applicable to other populations is uncertain.
There was no clinical benefit of administering hydroxychloroquine 600 mg per day for 8 weeks as PrEP to health care workers who were exposed to patients with COVID-19. Compared to placebo, hydroxychloroquine was associated with an increased risk of mostly mild adverse events.
Hydroxychloroquine as Pre-Exposure Prophylaxis for COVID-19 in Health Care Workers: A Randomized Trial
COVID PREP was a double-blind, placebo-controlled randomized clinical trial that investigated whether hydroxychloroquine 400 mg given once- or twice-weekly for 12 weeks can prevent SARS-CoV-2 infection in health care workers who were at high risk of exposure. The primary outcome was COVID-19-free survival time. Diagnosis of COVID-19 was defined as having laboratory-confirmed SARS-CoV-2 infection or having cough, shortness of breath, or difficulty breathing or having two or more of the following symptoms: fever, chills, rigors, myalgia, headache, sore throat, or new olfactory and taste disorders. COVID-19-compatible illness was included as a primary outcome even if a SARS-CoV-2 PCR test was not performed or if it was performed and the result was negative.25Study Population
- The study participants had to be working in the ED, in the intensive care unit, on a dedicated COVID-19 hospital ward, or as a first responder; alternatively, they had to have a job description that included regularly performing aerosol-generating procedures.
- Participants were recruited via social media platforms. Informed consent was obtained remotely, and the study drug was delivered to the participants by couriers.
- The study was powered based on an anticipated 10% event rate of new symptomatic infections. The investigators determined that the study needed to enroll 1,050 participants per arm to have 80% power. However, it became apparent before the first interim analysis that the study would not meet the enrollment target. As a result, enrollment was stopped without unblinding. The investigators attributed the marked decline in enrollment to the negative reports on the safety of hydroxychloroquine, including a warning from the FDA.
- Among the 1,483 participants who were randomized, baseline characteristics were similar across the study arms.
- The number of individuals who met the primary endpoint of confirmed or suspected SARS-CoV-2 infection was 39 (7.9%) in the placebo arm and 29 (5.9%) in both the once- and twice-weekly hydroxychloroquine arms. Among the 97 participants, only 17 were confirmed to be SARS-CoV-2 PCR positive.
- Compared to placebo, the hazard ratio for the primary endpoint was 0.72 (95% CI, 0.4–1.16; P = 0.18) for the once-weekly hydroxychloroquine arm and 0.74 (95% CI, 0.46–1.19; P = 0.22) for the twice-weekly hydroxychloroquine arm.
- There were no significant differences for any of the secondary efficacy endpoints among the three arms.
- There were significantly more adverse events reported in the once- and twice-weekly hydroxychloroquine arms (adverse events occurred in 31% vs. 36% of participants, respectively; P < 0.001 for both arms) than in the placebo arm (21% of participants). The most common adverse events were upset stomach and nausea.
- Drug concentrations were measured in dried whole blood samples from a subset of 180 participants who received hydroxychloroquine. The median hydroxychloroquine concentrations for the twice- and once-weekly hydroxychloroquine arms were 200 ng/mL and 98 ng/mL, respectively; both concentrations are substantially below the in vitro half-maximal effective concentration (EC50) of hydroxychloroquine. The investigators noted that the simulations that were used to determine the hydroxychloroquine dose for the study predicted much higher drug concentrations than the observed levels.
- The study was prematurely halted due to poor enrollment; therefore, the study population was insufficient to detect differences in outcomes among the study arms.
- The study only assessed the SARS-CoV-2 inhibitory activity of two doses of hydroxychloroquine, neither of which achieved concentrations that exceeded the in vitro EC50 of the drug.
- Only 17.5% of the participants who met study endpoints had positive SARS-CoV-2 test results; the remainder had COVID-19-compatible symptoms without a confirmatory diagnosis.
Hydroxychloroquine 400 mg once- or twice-weekly did not reduce the incidence of documented SARS-CoV-2 infection or COVID-19-compatible symptoms among health care workers who were at high risk of exposure. These findings suggest that hydroxychloroquine was not effective for SARS-CoV-2 PrEP or that the dose used for PrEP was suboptimal.
- The Panel recommends against the use of hydroxychloroquine for SARS-CoV-2 post-exposure prophylaxis (PEP) (AI).
- The Panel recommends against the use of other drugs for SARS-CoV-2 PEP, except in a clinical trial (AIII).
Several randomized controlled trials have evaluated the use of hydroxychloroquine for SARS-CoV-2 PEP.26-28 None of these studies have reported any evidence of efficacy, and all showed a higher frequency of adverse events among participants who received hydroxychloroquine than among control participants. The results of some of these studies are described below.
A number of agents (e.g., anti-SARS-CoV-2 monoclonal antibodies, hyperimmune gammaglobulin, convalescent plasma, ivermectin, 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.
Clinical Trial Data
Both chloroquine and hydroxychloroquine have in vitro activity against SARS-CoV and SARS-CoV-2.29,30 A small cohort study without a control group suggested that hydroxychloroquine might reduce the risk of SARS-CoV-2 transmission to close contacts.31
Household-Randomized, Double-Blind, Controlled Trial of SARS-CoV-2 Post-Exposure Prophylaxis With Hydroxychloroquine
A household-randomized, double-blind, controlled trial evaluated the use of hydroxychloroquine as PEP to prevent SARS-CoV-2 infection. The study was conducted at seven institutions in the United States between March and August 2020. Participants were recruited using online advertising, social media, and referrals from hospitals, health departments, and individuals with laboratory-confirmed SARS-CoV-2 infection.26
Households were randomized to receive oral hydroxychloroquine 400 mg once daily for 3 days, followed by hydroxychloroquine 200 mg once daily for an additional 11 days, or oral ascorbic acid 500 mg once daily for 3 days, followed by ascorbic acid 250 mg once daily for 11 days. Mid-turbinate nasal swabs were collected daily during the first 14 days, with the primary endpoint being PCR-confirmed SARS-CoV-2 infection within 14 days after enrollment in those who were not infected at baseline.Study Population
- Eligible participants had close contact with a SARS-CoV-2-infected person, which included household contacts or other close contacts (82%) or health care workers (18%) who cared for an infected person without wearing appropriate PPE. Participants must have come into contact with an index person who had received a diagnosis of SARS-CoV-2 infection within the past 14 days, and high-risk exposure to the index people must have occurred within the previous 96 hours.
- Enrollment included 829 participants from 671 households; 407 participants (in 337 households) received hydroxychloroquine, and 422 participants (in 334 households) received ascorbic acid.
- A total of 98 SARS-CoV-2 infections were detected during the first 14 days of follow-up, with an overall cumulative incidence of 14.3% (95% CI, 11.5% to 17%). Fifty-three events (i.e., PCR-confirmed SARS-CoV-2 infection) occurred in the hydroxychloroquine arm, and 45 events occurred in the control arm (aHR 1.10; 95% CI, 0.73–1.66; P > 0.20)
- In preplanned analyses, hazard ratios were not significantly different within subgroups based on type of contact, time between the most recent contact and the first dose of the study drug, duration of contact, number of contacts enrolled within the household, quarantine status, index case symptoms, or number of adults or children in the household.
- Adverse events that are associated with the use of hydroxychloroquine, including gastrointestinal symptoms and rash, occurred in 112 participants: 66 participants (16.2%) in the hydroxychloroquine arm and 46 participants (10.9%) in the control arm (P = 0.026).
- There was an average window of 2 days between the time of the most recent exposure to the index people and the time the study drugs were administered. The lapse of time between exposure to SARS-CoV-2 and initiation of hydroxychloroquine may have affected the efficacy of the drug as PEP.
- The primary analysis excluded approximately 10% of enrolled people who were shown to have SARS-CoV-2 infection at baseline.
In this study, hydroxychloroquine was ineffective when used as PEP for SARS-CoV-2 infection. Participants who received hydroxychloroquine had a greater risk of adverse events than those who received ascorbic acid.
Double-Blind Randomized Controlled Trial of Hydroxychloroquine as Post-Exposure Prophylaxis in Contacts With High-Risk or Moderate-Risk Occupational or Household Exposures
This double-blind randomized controlled trial included 821 participants who self-enrolled in the study using an internet-based survey. Participants were randomized to receive either hydroxychloroquine (hydroxychloroquine 800 mg once, followed by hydroxychloroquine 600 mg 6 to 8 hours later, and then hydroxychloroquine 600 mg once daily for 4 additional days) or placebo. Because enrollment was done online, the study drugs were sent to participants by overnight mail; consequently, more than 50% of the participants started the first dose of their assigned treatment 3 to 4 days after exposure to SARS-CoV-2.28Study Population
- Participants had a high or moderate risk of occupational exposure (66% of participants) or household exposure (34% of participants) to SARS-CoV-2.
- High-risk exposure was defined as being within six feet of an individual with confirmed SARS-CoV-2 infection for more than 10 minutes while not wearing a face mask or eye shield (87.6% of participants). Moderate-risk exposure was defined as exposure from the same distance and for the same duration while wearing a face mask but no eye shield (12.4% of participants).
- A total of 107 participants developed the primary outcome of symptomatic illness. Illness was confirmed by a positive result on a SARS-CoV-2 molecular test. If testing was not available, participants were considered to have symptomatic illness if they developed a compatible COVID-19-related syndrome based on CDC criteria.
- Due to limited access to molecular diagnostic testing, SARS-CoV-2 infection was confirmed in only 16 of the 107 participants (15%). There was no statistically significant difference in the incidence of the primary outcome (symptomatic illness) between the hydroxychloroquine arm and the placebo arm (11.8% vs. 14.3%, respectively; P = 0.35).
- There were more adverse events in the hydroxychloroquine arm (mostly nausea, loose stools, and abdominal discomfort), and no serious adverse events or cardiac arrhythmias in either arm.
- Most participants did not start their assigned therapy until at least 3 days after exposure to SARS-CoV-2.
- Only 15% of participants who reached the primary outcome had SARS-CoV-2 infection confirmed by molecular diagnostics.
- The study participants were young (median age was 40 years) and had a relatively low risk of severe COVID-19.
There was no difference in the incidence of observed symptomatic COVID-19 between participants who received hydroxychloroquine 600 mg once daily and those who received placebo. Although hydroxychloroquine 600 mg per day was associated with an increased frequency of adverse events, these adverse events were mostly mild.
Cluster-Randomized Trial of SARS-CoV-2 Post-Exposure Prophylaxis With Hydroxychloroquine
This open-label, cluster-randomized trial included 2,314 asymptomatic contacts of 672 COVID-19 cases in Spain.27 Participants who were epidemiologically linked to a PCR-positive COVID-19 case were defined as study clusters (called rings). All contacts in a ring were simultaneously cluster-randomized in a 1:1 ratio to the control arm (usual care) or the intervention arm (hydroxychloroquine 800 mg once daily for 1 day, followed by hydroxychloroquine 400 mg once daily for 6 days). Participants were informed of their allocated study arm after being randomized to the intervention or control arm and signing a consent form.
The primary outcome was onset of laboratory-confirmed COVID-19, which was defined as a positive result on a SARS-CoV-2 PCR test and at least one of the following symptoms: fever, cough, difficulty breathing, myalgia, headache, sore throat, new olfactory and taste disorders, or diarrhea. A secondary outcome was onset of SARS-CoV-2 infection, which was defined as either a positive SARS-CoV-2 PCR test result or the presence of any of the symptoms compatible with COVID-19. An additional secondary outcome was development of serological positivity at Day 14.Study Population
- Study participants were health care or nursing home workers (60.3%), household contacts (27.1%), or nursing home residents (12.7%) who were documented to have spent >15 minutes within two meters of a PCR-positive COVID-19 case during the 7 days prior to enrollment.
- The baseline characteristics of the participants were similar between the two study arms, including comorbidities, number of days of exposure to SARS-CoV-2 before enrollment and randomization, and type of contact.
- A total of 138 study participants (6.0%) developed PCR-confirmed, symptomatic SARS-CoV-2 infection. There was no statistical difference in the incidence of confirmed infection between the hydroxychloroquine and control arms (5.7% vs. 6.2%, respectively; risk ratio 0.86; 95% CI, 0.52–1.42).
- There was no statistical difference between the study arms in the incidence of either PCR-confirmed or symptomatically compatible COVID-19, which was 18.2% overall (18.7% in the hydroxychloroquine arm vs. 17.8% in the control arm; risk ratio 1.03; 95% CI, 0.77–1.38).
- There was no statistical difference between the arms in the rate of positivity for SARS-CoV-2 IgM and/or IgG (14.3% in the hydroxychloroquine arm vs. 8.7% in the control arm; risk ratio 1.57; 95% CI, 0.94–2.62).
- A greater percentage of patients in the hydroxychloroquine arm experienced adverse events (56.1%) than in the control arm (5.9%), although most of the adverse events were mild. Common adverse events included gastrointestinal events, nervous system disorders, myalgia, fatigue, and malaise. No serious adverse events were attributed to the study drug.
- The study lacked a placebo comparator, which could have had an impact on safety reporting.
- Data regarding the extent of the exposure to the index cases was limited.
- For >50% of the study participants, the time from exposure to the index case to randomization was ≥4 days.
The hydroxychloroquine regimen used for PEP in this study did not prevent SARS-CoV-2 infection in healthy individuals who were exposed to a PCR-positive case.
High concentrations of ivermectin have been shown to inhibit SARS-CoV-2 replication in vitro.32,33 Population data also indicate that country-wide mass use of prophylactic chemotherapy for parasitic infections, including the use of ivermectin, is associated with a lower incidence of COVID-19.34 At this time, few clinical trials have evaluated the safety and efficacy of ivermectin for SARS-CoV-2 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. The results of these trials are described below.
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.35 An open-label randomized controlled trial investigated ivermectin prophylaxis (plus personal protective measures [PPMs]) in health care workers (as PrEP) or in household contacts (as PEP) exposed to patients with laboratory-confirmed COVID-19. The incidence of SARS-CoV-2 infection was lower among the participants who received ivermectin than among control participants who used only PPMs. However, the study provided no data on the characteristics of the study participants, types of exposures, or how endpoints were defined.36 Finally, 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.37
Several clinical trials that are evaluating the use of ivermectin for SARS-CoV-2 PrEP or PEP are currently underway or in development. Please see ClinicalTrials.gov for the latest information.
- Centers for Disease Control and Prevention. SARS-CoV-2 Transmission. 2021.Available at: https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/sars-cov-2-transmission.html. Accessed June 2, 2021.
- Centers for Disease Control and Prevention. Coronavirus disease 2019 (COVID-19): how to protect yourself & others. 2020. Available at: https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/prevention.html. Accessed June 17, 2021.
- Centers for Disease Control and Prevention. Coronavirus disease 2019 (COVID-19): infection control guidance for healthcare professionals about coronavirus (COVID-19). 2020. Available at: https://www.cdc.gov/coronavirus/2019-ncov/hcp/infection-control.html. Accessed June 17, 2021.
- Food and Drug Administration. Fact sheet for healthcare providers administering vaccine (vaccination providers): emergency use authorization (EUA) of the Pfizer-BioNTech COVID-19 vaccine to prevent coronavirus disease 2019 (COVID-19). 2020. Available at: https://www.fda.gov/media/144413/download.
- Food and Drug Administration. Fact sheet for healthcare providers administering vaccine (vaccination providers): emergency use authorization (EUA) of the Moderna COVID-19 vaccine to prevent coronavirus disease 2019 (COVID-19). 2020. Available at: https://www.fda.gov/media/144637/download.
- Food and Drug Administration. Fact sheet for healthcare providers administering vaccine (vaccination providers): emergency use authorization (EUA) of the Janssen COVID-19 vaccine to prevent coronavirus disease 2019 (COVID-19). 2021/ Available at: https://www.fda.gov/media/146304/download.
- Shimabukuro TT, Kim SY, Myers TR, et al. Preliminary findings of mRNA COVID-19 vaccine safety in pregnant persons. N Engl J Med. 2021;Published online ahead of print. Available at: https://www.ncbi.nlm.nih.gov/pubmed/33882218.
- Polack FP, Thomas SJ, Kitchin N, et al. Safety and efficacy of the BNT162b2 mRNA COVID-19 vaccine. N Engl J Med. 2020;383(27):2603-2615. Available at: https://www.ncbi.nlm.nih.gov/pubmed/33301246.
- Baden LR, El Sahly HM, Essink B, et al. Efficacy and safety of the mRNA-1273 SARS-CoV-2 vaccine. N Engl J Med. 2021;384(5):403-416. Available at: https://www.ncbi.nlm.nih.gov/pubmed/33378609.
- Angel Y, Spitzer A, Henig O,et al. Association between vaccination with BNT162b2 and incidence of symptomatic and asymptomatic SARS-CoV-2 infections among health care workers. JAMA. 2021;Published online ahead of print. Available at: https://pubmed.ncbi.nlm.nih.gov/33956048/ .
- Centers for Disease Control and Prevention. Interim considerations: preparing for the potential management of anaphylaxis after COVID-19 vaccination. 2020. Available at: https://www.cdc.gov/vaccines/covid-19/info-by-product/pfizer/anaphylaxis-management.html. Accessed June 17, 2021.
- Centers for Disease Control and Prevention. Reported adverse events. 2021. Available at: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/adverse-events.html. Accessed June 2, 2021.
- Centers for Disease Control and Prevention. Safety of COVID-19 vaccines. 2021. Available at: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/safety-of-vaccines.html. Accessed June 2, 2021.
- Centers for Disease Control and Prevention. J&J/Janssen update. 2021. Available at: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/JJUpdate.html#symptoms-list. Accessed June 2, 2021.
- See I, Su JR, Lale A, et al. U.S. case reports of cerebral venous sinus thrombosis with thrombocytopenia after Ad26.COV2.S aaccination, March 2 to April 21, 2021. JAMA. 2021;Published online ahead of print. Available at: https://www.ncbi.nlm.nih.gov/pubmed/33929487.
- Greinacher A, Thiele T, Warkentin TE, Weisser K, Kyrle PA,Eichinger S. Thrombotic thrombocytopenia after ChAdOx1 nCov-19 vaccination. N Engl J Med. 2021;384(22):2092-2101. Available at: https://www.ncbi.nlm.nih.gov/pubmed/33835769.
- Pottegard A, Lund LC, Karlstad O, et al. Arterial events, venous thromboembolism, thrombocytopenia, and bleeding after vaccination with Oxford-AstraZeneca ChAdOx1-S in Denmark and Norway: population based cohort study. BMJ. 2021. Available at: https://www.bmj.com/content/373/bmj.n1114.
- Taquet M, Husain M, Geddes JR, Luciano S, Harrison PJ,et al. Cerebral venous thrombosisand portal vein thrombosis: a retrospective cohort study of 537,913 COVID-19 cases. 2021. Available at: https://osf.io/a9jdq/. Accessed June 2, 2021.
- American Society of Hematology, Bussel JB, Connors JM, et al. Thrombosis with thrombocytopenia syndrome (also termed vaccine-induced thrombotic thrombocytopenia). 2021. Available at: https://www.hematology.org/covid-19/vaccine-induced-immune-thrombotic-thrombocytopenia. Accessed June 2, 2021.
- American Heart Association, American Stroke Association, Furie KL. Diagnosis and management of cerebral venous sinus thrombosis with vaccine-induced immune thrombotic thrombocytopenia. 2021. Available at: https://www.ahajournals.org/doi/pdf/10.1161/STROKEAHA.121.035564.
- The American College of Obstetricians and Gynecologists. Practice advisory: vaccinating pregnant and lactating patients against COVID-19. 2020. Available at: https://www.acog.org/clinical/clinical-guidance/practice-advisory/articles/2020/12/vaccinating-pregnant-and-lactating-patients-against-covid-19. Accessed May 26, 2021.
- Centers for Disease Control and Prevention. Current COVID-19 ACIP vaccine recommendations. 2020. Available at: https://www.cdc.gov/vaccines/hcp/acip-recs/vacc-specific/covid-19.html. Accessed January 6, 2021.
- Centers for Disease Control and Prevention. When you've been fully vaccinated: how to protect yourself and others. 2021. Available at: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/fully-vaccinated.html. Accessed April 8, 2021.
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