Annual vaccination in the US against influenza A and B viruses is recommended for everyone ≥6 months old without a contraindication. Influenza vaccines available in the US for the 2024-2025 season are listed in Table 2.

Influenza is generally a self-limited illness, but pneumonia, respiratory failure, and death can occur, especially in patients at increased risk for influenza complications (see Table 1). Antiviral drugs recommended for treatment and chemoprophylaxis of influenza for the 2023-2024 season are listed in Table 2. Updated information on influenza activity and antiviral resistance is available from the CDC at www.cdc.gov/flu.

View the Comparison Chart: Antiviral Drugs for Influenza for 2023-2024

Annual vaccination in the US against influenza A and B viruses is recommended for everyone ≥6 months old without a contraindication. Influenza vaccines that are available in the US for the 2023-2024 season are listed in Table 2.

Annual vaccination in the US against influenza A and B viruses is recommended for everyone ≥6 months old without a contraindication. Influenza vaccines that are available in the US for the 2023-2024 season are listed in Table 2.

Influenza is generally a self-limited illness, but complications such as pneumonia, respiratory failure, and death can occur, especially in patients at increased risk for influenza complications (see Table 1). Antiviral drugs recommended for treatment and chemoprophylaxis of influenza this season are listed in Table 2. Updated information on influenza activity and antiviral resistance is available from the CDC at www.cdc.gov/flu. None of the drugs that are FDA-approved for treatment of influenza have clinically relevant antiviral activity against SARS-CoV-2.

View the Comparison Chart: Antiviral Drugs for Influenza for 2022-2023

Annual vaccination in the US against influenza A and B viruses is recommended for everyone ≥6 months old without a contraindication. Influenza vaccines that are available in the US for the 2022-2023 season are listed in Table 2.

Influenza is generally a self-limited illness, but complications such as pneumonia, respiratory failure, and death can occur, especially in patients at higher risk for complications (see Table 1). Antiviral drugs recommended for treatment and chemoprophylaxis of influenza this season are listed in Table 2. Updated information on influenza activity and antiviral resistance is available from the CDC at www.cdc.gov/flu.

View the Comparison Chart: Antiviral Drugs for Influenza for 2021-2022

Annual vaccination against influenza A and B viruses is recommended for everyone ≥6 months old without a contraindication.1 Available influenza vaccines for the 2021-2022 season are listed in Table 2.

The oral polymerase acidic endonuclease inhibitor baloxavir marboxil (Xofluza — Genentech) is now FDAapproved for post-exposure prophylaxis of influenza in patients ≥12 years old. Baloxavir was approved for treatment of acute uncomplicated influenza in patients ≥12 years old in 2018.1 Two neuraminidase inhibitors are FDA-approved for prophylaxis of influenza: oseltamivir (Tamiflu, and generics) in patients ≥1 year old, and zanamivir (Relenza) in patients ≥5 years old.2 Unlike oseltamivir and zanamivir, baloxavir is not FDA-approved for pre-exposure prophylaxis of influenza during institutional or community outbreaks.

Influenza is generally a self-limited illness, but complications such as pneumonia, respiratory failure, and death can occur, especially in patients at increased risk for influenza complications (see Table 1). Antiviral drugs recommended for treatment and chemoprophylaxis of influenza this season are listed in Table 2. Updated information on influenza activity and antiviral resistance is available from the CDC at www.cdc.gov/flu.

View the Comparison Chart: Antiviral Drugs for Influenza

Remdesivir (Veklury – Gilead), an investigational antiviral drug administered by IV infusion, is now available through an FDA Emergency Use Authorization (EUA) for treatment of COVID-19 in all hospitalized patients. An earlier EUA limited use of the drug to patients hospitalized with severe disease.

Annual vaccination against influenza A and B viruses is recommended for everyone ≥6 months old without a contraindication. Vaccination of all eligible persons can reduce the prevalence of influenza illness and symptoms that might be confused with those of COVID-19. Available vaccines and recommendations for specific patient populations for the 2020-2021 season are listed in Tables 2 and 3. Lower rates of influenza illness have been observed this season in the Southern Hemisphere, probably because of masking, social distancing, school closures, and travel restrictions.

Healthcare providers are often asked if drugs can be used past their expiration date. Because of legal restrictions and liability concerns, manufacturers do not sanction such use and usually do not comment on the safety or effectiveness of their products beyond the date on the label. Since our last article on this subject, more data have become available.

The severity and rapid spread of COVID-19 (caused by SARS-CoV-2) have raised questions about the use of some drugs in patients with the disease and whether currently available drugs could be effective in treating it. Definitive answers are lacking, but some recommendations can be made. For additional information on specific drugs, see our table Some Drugs Being Considered for Treatment of COVID-19.

View the Table: Treatments Considered for COVID-19

The severity and rapid spread of COVID-19 (caused by SARS-CoV-2) have raised questions about the use of some drugs in patients with the disease and whether currently available drugs could be effective in treating it. Definitive answers are lacking, but some recommendations can be made. For additional information on specific drugs, see our table Some Drugs Being Considered for Treatment of COVID-19.

Influenza is generally a self-limited illness, but pneumonia, respiratory failure, and death can occur. FDA-approved antiviral drugs for influenza are listed in Table 2. The neuraminidase inhibitors oseltamivir (Tamiflu, and generics), which is taken orally, and zanamivir (Relenza), which is inhaled, are approved for prophylaxis and treatment of acute uncomplicated influenza. The IV neuraminidase inhibitor peramivir (Rapivab) and the oral polymerase acidic (PA) endonuclease inhibitor baloxavir marboxil (Xofluza) are approved only for treatment. All of these drugs are active against both influenza A and influenza B viruses. Updated information on influenza activity and antiviral resistance is available from the CDC at www.cdc.gov/flu.

View the Expanded Table: Antiviral Drugs for Influenza

Patients may ask about taking elderberry for prevention and treatment of influenza. Products containing elderberry are promoted for relief of cold and flu symptoms and as an immune system booster.

View the Expanded Table: Antiviral Drugs for Seasonal Influenza

Antiviral drugs can be used for treatment and prophylaxis of seasonal influenza (see Table 1). Frequently updated information on influenza activity, influenza testing, and antiviral resistance is available from the CDC at www.cdc.gov/flu.

The FDA has approved baloxavir marboxil (Xofluza – Shionogi/Genentech), the first polymerase acidic (PA) endonuclease inhibitor, for single-dose, oral treatment of acute uncomplicated influenza in patients ≥12 years old. Baloxavir is the first drug with a new mechanism of action to be approved for treatment of influenza in almost 20 years.

Antiviral drugs can be used for treatment and prophylaxis of influenza. Frequently updated information on influenza activity, testing for influenza, and antiviral resistance is available from the CDC at www.cdc.gov/flu.

Antiviral drugs can be used for prophylaxis and treatment of influenza. Frequently updated information on influenza activity, testing for influenza, and antiviral resistance is available from the CDC at www.cdc.gov/flu.

Antiviral drugs can be used for treatment of influenza and as an adjunct to influenza vaccination1 for prophylaxis. Frequently updated information on influenza activity and antiviral resistance is available from the CDC at www.cdc.gov/flu.

The FDA has approved peramivir (Rapivab – BioCryst), an IV neuraminidase inhibitor administered as a single dose, for treatment of acute uncomplicated influenza in patients ≥18 years old who have had symptoms for no more than 2 days. Peramivir was available temporarily in the US during the 2009-2010 influenza season under an emergency use authorization for treatment of hospitalized patients. It has been available in some Asian countries since 2010. Peramivir is the third neuraminidase inhibitor to be approved in the US. Oseltamivir (Tamiflu), which is taken orally, and zanamivir (Relenza), which is inhaled, are approved for prophylaxis and treatment of influenza in children and adults.

Some readers of our article on Antiviral Drugs for Seasonal Influenza have expressed concerns regarding our recommendation for use of the oral neuraminidase inhibitor oseltamivir (Tamiflu) to treat high-risk patients with confirmed or suspected influenza illness, citing the British Medical Journal and The Cochrane Collaboration, which have contended that there is no acceptable evidence that the drug prevents complications or hospitalizations and have questioned the completeness of the results of controlled trials conducted by the manufacturer (Roche).

The CDC has announced that the most common influenza viruses circulating now are influenza A H3N2, which tend to cause more severe disease, and that about half of these viruses are antigenically different from the H3N2 strain in this year’s flu vaccine.1 Vaccination may still have a protective effect, even against drifted variants, and patients who have not received this year’s vaccine2 should be encouraged to do so.

Prompt treatment of confirmed or suspected influenza illness with antiviral drugs is recommended for hospitalized patients, for those with severe, complicated, or progressive illness, and for persons at high risk of complications: children <2 years old, adults ≥65 years old, women who are pregnant or ≤2 weeks postpartum, persons <19 years old receiving long-term aspirin therapy, morbidly obese patients (BMI ≥40), persons of American Indian/Alaskan Native heritage, residents of nursing homes or chronic-care facilities, and patients who are immunosuppressed or have chronic diseases such as asthma, diabetes, or heart, lung, or kidney disease.

The neuraminidase inhibitors oseltamivir (Tamiflu), which is taken orally, and zanamivir (Relenza), which is inhaled, taken within 48 hours after the onset of illness can decrease the duration of fever and symptoms in uncomplicated influenza and may reduce the incidence of pneumonia and death in high-risk patients.3 All of the influenza viruses tested to date for resistance to neuraminidase inhibitors this season have been susceptible to both oseltamivir and zanamivir.1

1. CDC health advisory regarding the potential for circulation of drifted influenza A (H3N2) viruses. Available at http://emergency.cdc.gov. Accessed December 18, 2014.
2. Influenza vaccine for 2014-2015. Med Lett Drugs Ther 2014; 56:97.
3. Antiviral drugs for seasonal influenza 2014-2015. Med Lett Drugs Ther 2014; 56:121.

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Antiviral drugs can be used for treatment of influenza and as an adjunct to influenza vaccination for prophylaxis. Frequently updated information on influenza activity and antiviral resistance is available from the CDC at www.cdc.gov/flu.

Antiviral drugs can be used for treatment of influenza and as an adjunct to influenza vaccination for prophylaxis. Frequently updated information on antiviral resistance is available at www.cdc.gov.

The drugs of choice for treatment of viral infections (other than HIV) and their dosages are listed in Tables 1-6 on the pages that follow. Some of the indications and dosages recommended here have not been approved by the FDA. Vaccines used for the prevention of viral infections are discussed elsewhere.

Antiviral drugs can be used as an adjunct to vaccination for prophylaxis and treatment of influenza. In recent years, the susceptibility of circulating influenza virus strains has evolved rapidly and treatment recommendations have changed during the influenza season. Frequently updated information on antiviral resistance is available at www.cdc.gov/flu/professionals/antivirals.

Antiviral drugs can be used for treatment and prophylaxis of influenza. In recent years, the susceptibility of circulating influenza strains has evolved rapidly and treatment recommendations have changed during the influenza season. The CDC influenza website provides frequently updated information on antiviral resistance (www.cdc.gov/flu).

Antiviral drugs can be used for treatment of patients with influenza and for prophylaxis when exposure to the disease occurs before or less than 2 weeks after vaccination. They can also be used to control institutional outbreaks of influenza. In recent years, the susceptibility of circulating influenza strains has evolved rapidly and treatment recommendations have changed during the influenza season. The CDC influenza web site provides frequently updated information on antiviral resistance (www.cdc.gov/flu)

The drugs of choice for treatment of non-HIV viral infections and their dosages are listed in Tables 1-6 on the pages that follow. Some of the indications and dosages recommended here have not been approved by the FDA. Vaccines used for the prevention of viral infections are discussed in another issue of Treatment Guidelines.

Currently circulating influenza virus is almost universally pandemic 2009 influenza A H1N1, but seasonal influenza strains could also appear soon. Antiviral drugs are an important adjunct to influenza vaccination for treatment and chemoprophylaxis of both pandemic and seasonal influenza. They may, however, interfere with the efficacy of FluMist, the live-attenuated intranasal vaccine, if they are administered within 48 hours before or <2 weeks after FluMist administration. Inactivated vaccines are not affected by antiviral drug therapy.

Since publication of our recent article on antiviral drugs for influenza, increased levels of resistance to oseltamivir (Tamiflu) have been detected in influenza A H1N1 strains.

Antiviral drugs are an important adjunct to influenza vaccination and can be used for treatment of patients with influenza within 2 days of the onset of illness and for chemoprophylaxis of influenza exposures that occur before or less than 2 weeks after vaccination. Patients who are immunocompromised or immunosuppressed, have pulmonary disease, are elderly or are healthcare workers may also be appropriate candidates for chemoprophylaxis.

Many drugs can cause psychiatric symptoms, but a causal connection is often difficult to establish. Psychiatric symptoms that emerge during drug treatment could also be due to the underlying illness, previously unrecognized psychopathology, or psychosocial factors. The withdrawal of some drugs can cause symptoms such as anxiety, psychosis, delirium, agitation or depression.

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Recent reports (D Kaye.Clin Infect Dis April 1, 2008;46:iii) indicate that 2 of the 3 components of this year's influenza vaccine (Med Lett Drugs Ther 2007;49:81), the influenza B and A/H3N2 antigens, do not matchup well with circulating strains. The B component is probably not protective. The A/H3N2 antigen in the vaccine probably provides some protection, particularly for high-risk patients. The third component, the A/H1N1 antigen, is protective against circulating A/H1N1 influenza viruses, but these viruses, unlike previous A/H1N1 strains, are developing some resistance to oseltamivir (Tamiflu), particularly in Europe; in the US and Canada, about 5% of influenza A/H1N1 isolates are resistant to oseltamivir in vitro.

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Antiviral drugs can be used for treatment of patients with influenza and for prophylaxis of influenza exposures that occur before or less than 2 weeks after vaccination. They can also be used to control institutional influenza outbreaks and for prophylaxis in years when circulating strains differ from those included in the vaccine.

The drugs of choice for treatment of non-HIV viral infections with their dosages and cost are listed in Tables 1-6. Some of the indications and dosages recommended here have not been approved by the FDA. Vaccines used in the prevention of viral infections are discussed in the "Adult Immunization" issue of Treatment Guidelines.

Antiviral drugs can be used to control institutional influenza outbreaks and for prophylaxis of influenza exposures that occur before or less than 2 weeks after vaccination with inactivated vaccine, or in years when circulating strains differ from those included in the vaccine. They can also be used for early treatment of patients with influenza.

Antiviral prophylaxis is indicated for influenza exposures that occur before (or less than 2 weeks after) vaccination with inactivated vaccine, or in years when circulating strains differ from those included in the vaccine. Antiviral drugs can also be used for treatment of patients who develop symptoms of influenza, regardless of vaccination status.
Please see Update: Influenza Resistance to Amantadine and Rimantadine

Annual immunization against influenza A and B is the most effective method of preventing infection and has been shown to reduce associated complications. A future issue of The Medical Letter will review drug prophylaxis and treatment of influenza.

The drugs of choice for non-HIV viral infections with their dosages and cost are listed in the tables that begin on page 24. Some of the indications and dosages recommended here have not been approved by the FDA.

Due to the unanticipated shortage in the US supply of inactivated influenza vaccine, many persons who normally would have received the vaccine will be unable to get it this year. Antiviral drugs can be used for prophylaxis of unvaccinated persons who are exposed to influenza, and for treatment of both vaccinated and unvaccinated patients who develop symptoms of the disease.

Unlike the last few years there is no early-season shortage of influenza vaccine. Immunization programs for all recommended individuals can proceed. There are 2 new influenza vaccine formulations available this year, FluMist, an intranasal vaccine and Fluzone, a pediatric formulation. Timing, indications, adverse effects, dosage and cost of the vaccines is discussed. The drugs that can be used for prophylaxis of influenza are also reviewed.

The choice of drugs for treatment of pneumonia depends on the most likely pathogens causing the infection and local antimicrobial resistance patterns. Factors such as severity of illness, presence of co-morbid conditions and whether the infection is community or hospital-acquired also need to be considered.

FluMist (MedImmune), the first live-attenuated and first intranasally administered influenza vaccine, has been approved by the FDA to prevent influenza in healthy people 5-49 years old. Given as a nasal spray, it stimulates immunity by viral replication in the upper respiratory tract. This vaccine apparently will be advertised directly to the public as a "needle-free" alternative to intramuscular influenza vaccine.

Influenza vaccine for the 2002-2003 season will include last year's A strains, A/New Caledonia/20/99 (H1N1)-like and A/Moscow/10/99 (H3N2)-like, and a new B strain, B/Hong-Kong/330/01-like (MMWR Morb Mortal Wkly Rep 2002; 51:503).

The drugs of choice for non-HIV viral infections with their dosages and cost are listed in the table that begins on the next page. Since the last Medical Letter issue on this subject, some new drugs and some new recommendations for old drugs have been added.

The centers for Disease Control and Prevention is anticipating a delay, but not a shortage, of influenza vaccine for the 2001-2002 season. Last year manufacturing problems led to a substantial delay in vaccine availability. This year's delay is being attributed, in part, to the dicontinuation of the Fluogen (King) brand of vaccine. The 2001-02 vaccine will include A/New Caledonia/20/99 (H1N1)-like, A/Moscow/10/99 (H3N2)-like, and B/Sichuan/379/99-like antigens.

The drugs of choice for non-HIV viral infections with their dosages and cost are listed in the [article's] table.

Zanamivir, a neuraminidase inhibitor taken by inhalation, has been approved by the FDA for treatment of influenza. Oseltamivir phosphate, an oral neuraminidase inhibitor, will probably be approved soon.