COVID-19

The risk of serious disease and death in COVID-19 cases increases in people over age 65, in people who smoke or previously smoked, and in people with other serious medical disorders, such as  

• Cancer

• Chronic heart, lung, kidney, or liver disease

• Diabetes

• Stroke or cerebrovascular disease

• Immunocompromising conditions

• HIV infection

• Tuberculosis

• Sickle cell disease

• Thalassemia

• Dementia

• Obesity

• Pregnancy (up to 42 days after pregnancy)

• Some types of disabilities

• Substance use disorders

• Physical inactivity

• Some mental health disorders such as depression and schizophrenia

(Also see CDC: COVID-19 Understanding Risk.)

Vaccination dramatically lowers the risk of severe illness for all age groups—lower vaccination rates in younger age groups has shifted the age demographic of hospitalized patients (see CDC: COVID Data Tracker).

In addition to respiratory disease that can progress to acute respiratory distress syndrome (ARDS) and death, other serious complications include the following:

• Heart disorders including arrhythmias, cardiomyopathy, and acute cardiac injury

• Coagulation disorders including thromboembolism and pulmonary emboli, disseminated intravascular coagulation (DIC), hemorrhage, and arterial clot formation

• Guillain-Barré syndrome (rare)

• Sepsis, shock, and multiorgan failure

A postinfectious inflammatory syndrome termed multisystem inflammatory syndrome in children (MIS-C) has been observed as a rare complication of SARS-CoV-2 infection. It has features similar to Kawasaki disease or toxic shock syndrome. Children with MIS-C most commonly present with fever, tachycardia, signs of systemic inflammation, and multisystem involvement (eg, cardiac, gastrointestinal, renal) at 2 to 6 months following a generally mild or even asymptomatic SARS-CoV-2 infection. Cases meeting the following criteria should be reported to local, state, or territorial health departments as suspected MIS-C: individuals < 21 years old with fever > 24 hours, laboratory evidence of inflammation, signs of severe multisystem (≥ 2 organs) involvement requiring hospitalization, and laboratory or epidemiologic association with recent SARS-CoV-2 infection (2). Vaccination appears to be highly protective against the development of MIS-C (2). A similar multisystem inflammatory syndrome in young and middle-aged adults (MIS-A) also has been reported (3).

In most patients, symptoms resolve within about a week. However, some patients begin with mild symptoms, then clinically deteriorate after a week, progressing to severe disease, including ARDS. Prolonged illness appears to be more common in those with severe disease, but even patients with mild illness may have persistent symptoms, including dyspnea, cough, and malaise that last for weeks or even months. Viral PCR tests in patients may remain positive for at least 3 months regardless of symptoms. However, even patients with lingering symptoms are generally not considered infectious, as virus is rarely able to be cultured from the upper respiratory tract of patients after 10 days of illness.

COVID-19 may also be associated with long-term sequelae following acute illness (4), and symptoms from post–COVID-19 conditions can linger for months. This has been referred to by many names, including long COVID, long-haul COVID, and post-acute COVID-19 syndrome or condition, and is estimated to impact 25 to 50% of all patients in some United States surveys. Fatigue, weakness, pain, myalgias, dyspnea, and cognitive dysfunction are commonly reported and can be associated with a poorer quality of life (5). Risk factors for long-term sequelae may include more severe disease presentation, older age, female sex, and pre-existing lung disease. An international case definition has been established to aid in the diagnosis and further investigation of this condition (6).

1. 1. Jansen L, Tegomoh B, Lange K, et al: Investigation of a SARS-CoV-2 B.1.1.529 (Omicron) variant cluster - Nebraska, November-December 2021. MMWR Morb Mortal Wkly Rep 70(5152):1782-2784, 2021. doi: 10.15585/mmwr.mm705152e3

2. 2. Miller AD, Yousaf AR, Bornstein E, et al: Multisystem inflammatory syndrome in children (MIS-C) during SARS-CoV-2 Delta and Omicron variant circulation - United States, July 2021-January 2022. Clin Infect Dis Jun 10;ciac471, 2022. doi: 10.1093/cid/ciac471

3. 3. Morris SB, Schwartz NG, Patel P, et al: Case series of multisystem inflammatory syndrome in adults associated with SARS-CoV-2 infection — United Kingdom and United States, March–August 2020. MMWR 69:1450–1456, 2020. doi: 10.15585/mmwr.mm6940e1

4. 4. Nalbandian A, Sehgal K, Gupta A, et al: Post-acute COVID-19 syndrome. Nat Med 27(4):601-615, 2021. doi: 10.1038/s41591-021-01283-z

5. 5. Han JH, Womack KN, Tenforde MW, et al: Associations between persistent symptoms after mild COVID-19 and long-term health status, quality of life, and psychological distress. Influenza Other Respir Viruses 16(4):680-689, 2022. doi:10.1111/irv.12980

6. 6. Soriano JB, Murthy S, Marshall JC, et al: A clinical case definition of post-COVID-19 condition by a Delphi consensus. Lancet Infect Dis 22(4):e102-e107, 2022. doi: 10.1016/S1473-3099(21)00703-9

Routine laboratory findings for those with more severe disease include lymphopenia as well as less specific findings of elevated aminotransaminase (ALT, AST) levels, elevated lactate dehydrogenase (LDH) levels, D-dimer, ferritin, and elevated inflammatory markers such as C-reactive protein.

Patients with dyspnea, hypoxia on home oximetry, or other concerning symptoms should be referred for in-person medical evaluation, including oxygen saturation measurement, and followed up with for signs of clinical deterioration.

Chest imaging findings can be normal with mild disease and increase with increasing severity of the illness. Typical findings are consistent with viral pneumonia and include ground-glass opacities and consolidation on either chest x-ray or chest CT. Chest imaging is not recommended as a routine screening tool for COVID-19.

1. 1. Drain PK: Rapid diagnostic testing for SARS-CoV-2. N Engl J Med 386(3):264-272, 2022. doi: 10.1056/NEJMcp2117115

2. 2. Ford L, Lee C, Pray IW, et al: Epidemiologic characteristics associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen-based test results, real-time reverse transcription polymerase chain reaction (rRT-PCR) cycle threshold values, subgenomic RNA, and viral culture results from university testing. Clin Infect Dis 73(6):e1348-e1355, 2021. doi: 10.1093/cid/ciab303

3. 3. Wu S, Archuleta S, Lim SM, et al: Serial antigen rapid testing in staff of a large acute hospital. Lancet Infect Dis 22(1):14-15, 2022. doi: 10.1016/S1473-3099(21)00723-4

4. 4. Dinnes J, Sharma P, Berhane S: Rapid, point-of-care antigen tests for diagnosis of SARS-CoV-2 infection. Cochrane Database Sys Rev July 22, 2022. doi: 10.1002/14651858.CD013705.pub3/full

Nirmatrelvir, an oral antiviral drug, given in combination with ritonavir taken together orally twice a day for 5 days. This drug treatment is not authorized for use for longer than 5 consecutive days. (See also the FDA EUA Factsheet.)

Nirmatrelvir is a protease inhibitor that cleaves a SARS-CoV-2 protein and therefore inhibits the virus from replicating. Ritonavir is a strong cytochrome P450 (CYP) 3A4 inhibitor and acts as a boosting agent; it slows down the metabolism of nirmatrelvir, causing it to remain in the body for a longer duration at higher concentrations.

nirmatrelvir/ritonavir combination given at ≤ 5 days after symptom onset reduced the proportion of people with COVID-19-related hospitalization or death from any cause through day 28 compared to placebo by 88% (0.8 versus 6.3%) (1).

Using the nirmatrelvir/ritonavir combination in people with uncontrolled or undiagnosed HIV-1 infection may lead to HIV-1 drug resistance. The nirmatrelvir/ritonavir combination may cause liver damage, so caution should be exercised in patients with preexisting liver disease, liver enzyme abnormalities, or hepatitis. The drug is not recommended in patients with severe liver disease.

In patients with moderate renal impairment, which is an estimated creatinine clearance (also called estimated glomerular filtration rate or eGFR) of 30 to 60 mL/minute, the dose is reduced to 150 mg nirmatrelvir (one 150-mg tablet) with 100 mg ritonavir (one 100-mg tablet), with both tablets taken together twice a day for 5 days. Nirmatrelvir/ritonavir combination is not recommended in patients with severe kidney impairment (eGFR < 30 mL/minute).

Return of symptoms has been reported in some patients after use of nirmatrelvir/ritonavir, and PCR and antigen tests for SARS-CoV-2 can become positive again, even in patients who remain asymptomatic. Additional treatment is not currently recommended, but patients should be advised to re-isolate if rebound symptoms or tests occur. (See also CDC: COVID-19 Rebound After Paxlovid Treatment.)

The nirmatrelvir/ritonavir combination drug has a variety of serious known and possible drug interactions; concomitant drugs must be screened for these prior to initiation of treatment. For a list of these drug interactions see the FDA EUA Fact Sheet.

an intravenous antiviral drug, is used to treat mild to moderate COVID-19 in adults and adolescents (≥ 12 years old and weighing ≥ 40 kilograms) who have positive results of direct SARS-CoV-2 viral testing and who are at high risk for progression to severe COVID-19. It should be initiated as soon as possible and within 7 days of symptom onset. The dose of a 3-day course of remdesivir is 200 mg IV on day 1 and 100 mg IV on days 2 and 3. The course can be extended to 5 days for patients who progress to severe disease.

Remdesivir was studied for this indication in a randomized controlled trial of 562 nonhospitalized patients age ≥ 12 years of age with symptomatic COVID-19 at high risk for progression to severe disease and who had not received a COVID-19 vaccine. Remdesivir given for 3 days and started within 7 days of symptom onset reduced hospitalization or death rates through day 28 compared to placebo by 87% (0.7 versus 5.3%) (2).

an oral antiviral drug, is a nucleoside analogue that works by introducing errors into the SARS-CoV-2 viral genome, which inhibits viral replication. It has received FDA EUA for treatment of mild to moderate COVID-19 in nonhospitalized adults ≥ 18 years of age who have positive results of direct SARS-CoV-2 viral testing and who are at high risk for progression to severe disease, including hospitalization or death, and for whom alternative COVID-19 treatment options authorized by the FDA are not accessible or clinically appropriate. Molnupiravir should be initiated as soon as possible after diagnosis of COVID-19 and within 5 days of symptom onset. Molnupiravir is administered as four 200-mg capsules taken orally every 12 hours for 5 days. It is not authorized for use for longer than 5 consecutive days. (See also the FDA EUA Fact Sheet for Molnupiravir.)

Molnupiravir may have an effect on the emergence of new SARS-CoV-2 variants based on a theoretical concern; however, the risk is believed to be low based on available genotoxicity data and the limited 5-day treatment course. Molnupiravir is not authorized for use in patients < 18 years of age because it may affect bone and cartilage growth. Molnupiravir is not recommended for use during pregnancy because animal reproduction studies suggested that molnupiravir may cause fetal harm when administered to pregnant patients. Females of childbearing potential are advised to use a reliable method of birth control correctly and consistently during treatment with molnupiravir and for 4 days after the final dose. Males of reproductive potential who are sexually active with females of childbearing potential are advised to use a reliable method of birth control correctly and consistently during treatment with molnupiravir and for at least 3 months after the final dose.

Molnupiravir was studied in a randomized, double-blind, placebo-controlled clinical trial of 1433 nonhospitalized patients ≥ 18 years of age with mild to moderate COVID-19 at high risk for progression to severe COVID-19 and/or hospitalization and who had not received a COVID-19 vaccine. Molnupiravir given for 5 days and started within 5 days of symptom onset reduced by 30% hospitalization or death rates through day 29 compared to placebo (6.8 versus 9.7%) (3).

are neutralizing anti-SARS-CoV-2 monoclonal antibody (mAb) therapies. The FDA currently recommends against their use in treatment of COVID-19 because the dominant Omicron subvariants are resistant to their neutralizing activity (see NIH: Anti-SARS-CoV-2 Monoclonal Antibodies).

Antiviral drugs are more likely to provide benefit earlier in the course when illness is a result of active viral replication, whereas anti-inflammatory and immunomodulatory therapies are better suited for later in the course when the host inflammatory response and immune dysregulation are driving the disease state. (Also see NIH: Therapeutic Management of Hospitalized Adults With COVID-19.)

For patients requiring supplemental oxygen but not additional respiratory support, treatment options include

The antiviral drug is used to treat adult and pediatric patients ≥ 28 days of age and weighing ≥ 3 kg who require hospitalization for COVID-19. The recommended dosage for adults and pediatric patients weighing ≥ 40 kg is a single loading dose of 200 mg on Day 1 via intravenous infusion followed by once-a-day maintenance doses of 100 mg from Day 2 via intravenous infusion. The recommended dosage for pediatric patients ≥ 28 days of age and weighing 3 kg to less than 40 kg is a single loading dose of 5 mg/kg on Day 1 via intravenous infusion followed by once-a-day maintenance doses of 2.5 mg/kg from Day 2 via intravenous infusion. The recommended treatment duration is 5 days but is approved for use up to 10 days in patients who require invasive mechanical ventilation and/or extracorporeal membrane oxygenation (ECMO). Benefits of antiviral treatment in this group though are inconclusive.

In a large randomized clinical trial (ACTT-1), remdesivir was associated with earlier clinical improvement for patients requiring supplemental oxygen but not mechanical ventilation or other higher levels of support (4). This improved time to recovery was also observed in an outpatient randomized controlled trial (PINETREE) (2). However, benefit was not observed in 2 open-label trials (Solidarity [5] and DisCoVeRy [6]).

Overall, studies of remdesivir support its use early in infection (prior to days 7 to 10) when active viral replication is more likely to be contributing to illness. Remdesivir can also be considered in patients who are hospitalized but not requiring supplemental oxygen, although data are lacking in this population. Remdesivir is not recommended for patients with an eGFR < 30 mL/minute. Renal function should be monitored before and during remdesivir treatment. (See also the NIH treatment guidelines on remdesivir.)

The corticosteroid (at a dosage of 6 mg once per day for up to 10 days or until hospital discharge, whichever comes first) is generally recommended in patients with COVID-19 who require supplemental oxygen, but its use is not recommended in patients who do not require supplemental oxygen. Dexamethasone showed a survival benefit for those requiring supplemental oxygen or mechanical ventilation in the RECOVERY trial (7). Its benefit is likely to be greatest in patients whose illness is due to the inflammatory response from infection. If dexamethasone

The combination of remdesivir and dexamethasone is commonly used in hospitalized patients requiring supplemental oxygen within the first 10 days of illness when both viral replication and host inflammation may be contributing to the clinical presentation.

For patients requiring noninvasive ventilation (including high flow oxygen delivery systems)

• Additional immunomodulatory drugs should be considered, particularly for patients with rapid deterioration or signs of systemic inflammation.

Additional immunomodulators include the JAK inhibitor 8], ACTT-2 [9]) and open label (REMAP-CAP [10], RECOVERY [11]) clinical trials that showed survival benefit with addition of one of these drugs in patients requiring this level of respiratory support. These drugs are potent immunosuppressants, and the potential benefit should be weighed against the additional immunosuppressive risk in patients with suspicion of a concomitant serious bacterial or fungal infection or at high risk for opportunistic infections due to an underlying immunosuppressive condition. See NIH treatment guidelines on immunomodulators for further details regarding appropriate patient selection for these therapies.

For patients requiring mechanical ventilation or ECMO,

Many therapies have been considered and are not currently recommended for the treatment or prevention of COVID-19:

• 12). Clinical recommendations for its use have not been published.

• Convalescent plasma is not currently recommended for the treatment of patients hospitalized with COVID-19. Data from a number of randomized clinical trials (13) and a large registry associated with an expanded access program failed to show a meaningful benefit in this population and suggest a potential association with increased need for mechanical ventilation. It may be considered in nonhospitalized patients with mild to moderate disease and high risk of progression to severe disease if no other treatment options are available.

• Nonspecific immunoglobulin (IVIG) and mesenchymal stem cell therapy are also not recommended. 

• Additional immunomodulatory therapies, including interferons, kinase inhibitors, and interleukin inhibitors have been used, but there are insufficient data to recommend their routine use outside of clinical trials.

• 14, 15). The combined lack of benefit and toxicities associated with chloroquine and hydroxychloroquine led to recommendations that they not be used for treatment of COVID-19 (see NIH COVID-19 Treatment Guidelines: Chloroquine or Hydroxychloroquine and/or Azithromycin).

• 16). A recent large randomized, placebo-controlled study showed no effect of ivermectin (17). The FDA and other organizations have issued warnings about toxicity from the inappropriate use of ivermectin preparations intended for large animal use (see FDA: Why You Should Not Use Ivermectin to Treat or Prevent COVID-19).

An NIH panel concluded there is insufficient evidence to recommend either for or against the use of ECMO in adults with COVID-19 and refractory hypoxemia (see NIH COVID-19 Treatment Guidelines: Extracorporeal Membrane Oxygenation [May 31, 2022]).

Complications of COVID-19 illness should be treated as they arise. Hospitalized patients with COVID-19 may be at increased risk for thromboembolic events. Guidelines around managing this increased risk are continually evolving as data emerge (see NIH: The COVID-19 Treatment Guidelines Panel's Statement on Anticoagulation in Hospitalized Patients With COVID-19). Currently, therapeutic anticoagulation should be considered in nonpregnant, hospitalized patients requiring supplemental oxygen but not intensive care if they have an elevated D-dimer and no serious bleeding risk. The risk of an adverse event from bleeding outweighs the potential benefit in critically ill patients. Pharmacologic venous thromboembolism prophylaxis should be considered for all other hospitalized patients.

Respiratory management of the nonintubated and intubated COVID-19 patient should take into consideration the tendency toward hypoxia. Nonpharmacologic adjunctive measures such as frequent repositioning and ambulation may be helpful.

1. 1. Hammond J, Leister-Tebbe H, Gardner A, et al: Oral nirmatrelvir for high-risk, nonhospitalized adults with Covid-19. N Engl J Med 386(15):1397-1408, 2022. doi: 10.1056/NEJMoa2118542

2. 2. Gottlieb RL, Vaca CE, Paredes R et al: Early remdesivir to prevent progression to severe covid-19 in outpatients. N Engl J Med 386(4):305-315, 2022. doi: 10.1056/NEJMoa2116846

3. 3. Jayk Bernal A, Gomes da Silva MM, Musungaie DB, et al: Molnupiravir for oral treatment of Covid-19 in nonhospitalized Patients. N Engl J Med 386(6):509-520, 2022. doi: 10.1056/NEJMoa2116044

4. 4. Beigel JH, Tomashek KM, Dodd LE, et al: Remdesivir for the treatment of Covid-19 - final report. N Engl J Med 383(19):1813-1826, 2020. doi: 10.1056/NEJMoa2007764

5. 5. WHO Solidarity Trial Consortium: Remdesivir and three other drugs for hospitalised patients with COVID-19: final results of the WHO Solidarity randomised trial and updated meta-analyses. Lancet 399(10339):1941-1953, 2022. doi: 10.1016/S0140-6736(22)00519-0

6. 6. Ader F, Bouscambert-Duchamp M, Hites M, et al: Remdesivir plus standard of care versus standard of care alone for the treatment of patients admitted to hospital with COVID-19 (DisCoVeRy): a phase 3, randomised, controlled, open-label trial. Lancet Infect Dis 22(2):209-221, 2022. doi: 10.1016/S1473-3099(21)00485-0

7. 7. RECOVERY Collaborative Group, Horby P, Lim WS, Emberson JR, et al: Dexamethasone in hospitalized patients with Covid-19. N Engl J Med 384(8):693-704, 2021. doi: 10.1056/NEJMoa2021436

8. 8. Marconi VC, Ramanan AV, de Bono S, et al: Efficacy and safety of baricitinib for the treatment of hospitalised adults with COVID-19 (COV-BARRIER): a randomised, double-blind, parallel-group, placebo-controlled phase 3 trial [published correction appears in Lancet Respir Med 2021 Oct;9(10):e102]. Lancet Respir Med 9(12):1407-1418, 2021. doi:10.1016/S2213-2600(21)00331-3

9. 9. Kalil AC, Patterson TF, Mehta AK, et al: Baricitinib plus remdesivir for hospitalized adults with Covid-19. N Engl J Med 384(9):795-807, 2021. doi:10.1056/NEJMoa2031994

10. 10. REMAP-CAP Investigators, Gordon AC, Mouncey PR, et al: Interleukin-6 receptor antagonists in critically ill patients with Covid-19. N Engl J Med 384(16):1491-1502, 2021. doi:10.1056/NEJMoa2100433

11. 11. RECOVERY Collaborative Group, Horby P, Lim WS, et al: Dexamethasone in hospitalized patients with Covid-19. N Engl J Med 384(8):693-704, 2021. doi:10.1056/NEJMoa2021436

12. 12. Vlaar APJ, Witzenrath M, van Paassen P, et al: Anti-C5a antibody (vilobelimab) therapy for critically ill, invasively mechanically ventilated patients with COVID-19 (PANAMO): a multicentre, double-blind, randomised, placebo-controlled, phase 3 trial. Lancet Respir Med 10(12):1137-1146, 2022. doi:10.1016/S2213-2600(22)00297-1

13. 13. Janiaud P, Axfors C, Schmitt AM, et al: Association of convalescent plasma treatment with clinical outcomes in patients with COVID-19: A systematic review and meta-analysis. JAMA 325(12);1185-1195, 2021, doi: 10.1001/jama.2021.2747

14. 14. Self WH, Semler MW, Leither LM, et al. Effect of hydroxychloroquine on clinical status at 14 days in hospitalized patients with COVID-19: a randomized clinical trial. JAMA 324(21):2165-2176, 2020. doi:10.1001/jama.2020.22240

15. 15. RECOVERY Collaborative Group, Horby P, Mafham M, et al. Effect of hydroxychloroquine in hospitalized patients with Covid-19. N Engl J Med 383(21):2030-2040, 2020. doi:10.1056/NEJMoa2022926

16. 16. Popp M, Stegemann M, Metzendorf MI, et al: Ivermectin for preventing and treating COVID-19. Cochrane Database Syst Rev. 7(7):CD015017, 2021. doi: 10.1002/14651858.CD015017.pub2

17. 17. Reis G,Silva EASM, Silva DCM, et al: Effect of early treatment with ivermectin among patients with COVID-19. N Engl J Med 386:1721-1731, 2022. doi: 10.1056/NEJMoa2115869

1. 1. Zhong D, Xiao S, Debes AK, et al: Durability of antibody levels after vaccination with mRNA SARS-CoV-2 vaccine in individuals with or without prior infection. JAMA 326(24):2524-2526, 2021. doi:10.1001/jama.2021.19996

For a detailed discussion of the vaccines approved in the United States, see COVID-19 vaccine.

Vaccination is the most effective way to prevent severe illness and death from COVID-19, including from the Delta and Omicron variants. In the United States in the fall of 2021, unvaccinated people were much more likely to die from COVID-19 than vaccinated people (with booster) (1).

In the United States, the CDC recommends nonimmunocompromised peopleCDC: Interim Clinical Considerations for Use of COVID-19 Vaccines in the United States). Children ages 6 months to 4 years should receive 1 to 3 doses of an mRNA 2023–2024 formulation (recommended doses and manufacturer vary depending on vaccination history), and children 5 to 11 years should receive 1 dose regardless of vaccination history of either mRNA 2023–2024 formulation. The CDC also recommends adults ages 65 years and over receive an additional updated 2023-2024 COVID-19 vaccine dose (see CDC: Older Adults Now Able to Receive Additional Dose of Updated COVID-19 Vaccine). Guidance for people who are moderately or severely immunocompromised can also be found at the CDC website. The updated 2023–­2024 vaccines target the XBB.1.5 Omicron variant. The 2023–­2024 formulation replaces the COVID-19 monovalent vaccines that targeted the original SARS-CoV-2 strain and the bivalent vaccines that targeted both the original virus and BA.4/BA.5 Omicron subvariants.

Multiple COVID-19 vaccines are currently in use worldwide. For more information on global vaccine approvals and clinical trials, see the UNICEF COVID-19 Vaccine Market Dashboard and the World Health Organization’s COVID-19 vaccine tracker and landscape.

mRNA vaccines do not contain viral antigen but rather deliver a small, synthetic piece of mRNA that encodes for the desired target antigen (the spike protein). After being taken up by cells of the immune system, the vaccine mRNA degrades after instructing the cell to produce viral antigen. The antigen is then released and triggers the desired immune response to prevent severe infection upon subsequent exposure to the actual virus.

Adenovirus vector vaccines contain a piece of the DNA, or genetic material, that is used to make the distinctive “spike” protein of the SARS-CoV-2 virus, which then triggers the desired immune response.

Protein subunit adjuvanted vaccines contain a recombinant SARS-COV-2 spike protein along with an adjuvant that triggers the desired immune response. This is a classic vaccine approach that has been used in the United States for over 30 years.

Two mRNA vaccines (2023–­2024 formulations of Moderna COVID-19 Vaccine and Pfizer-BioNTech COVID-19 Vaccine), and one protein subunit adjuvanted vaccine (2023–2024 formulation of Novavax COVID-19 Vaccine, Adjuvanted) are used in the United States (see CDC: COVID-19 Vaccination Clinical & Professional Resources). As of May 6, 2023, the adenovirus vector vaccine (Ad26.COV2.S) is no longer available for use in the United States due to the risk of serious adverse events. There is a plausible causal relationship between the adenovirus vector vaccine and a rare and serious adverse event—blood clots with low platelets (vaccine-induced thrombosis with thrombocytopenia syndrome, or VITTS).

In addition to staying up to date with COVID-19 vaccines, people can avoid being exposed to the virus by washing hands frequently, wearing face masks, maintaining social distance, avoiding poorly ventilated spaces and crowds, and taking other steps recommended by the Centers for Disease Control and Prevention (CDC). People should also have COVID-19 testing if they are exposed to an infected individual or have symptoms. Symptomatic individuals should follow recommendations for isolation.

To help prevent spread of SARS-CoV-2 from suspected cases, health care practitioners should use standard, contact, and airborne precautions with eye protection. Airborne precautions are particularly relevant for patients undergoing aerosol-generating procedures.

1. 1.  Johnson AG, Amin AB, Ali AR, et al: COVID-19 incidence and death rates among unvaccinated and fully vaccinated adults with and without booster doses during periods of delta and Omicron variant emergence — 25 U.S. Jurisdictions, April 4–December 25, 2021. MMWR Morb Mortal Wkly Rep 71:132–138. 2022. doi: 10.15585/mmwr.mm7104e2