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.

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

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.

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.

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.

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.

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.

Annual vaccination against influenza A and B viruses is recommended for everyone ≥6 months old without a contraindication. Available vaccines and recommendations for specific patient populations for the 2019-2020 season are listed in Tables 2 and 3.

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.

Persons planning to travel outside the US should be up to date on routine vaccines and, depending on their destination, duration of travel, and planned activities, may also receive certain travel-specific vaccines. Tickborne encephalitis and dengue vaccines, which are not available in the US, are reviewed in a separate article available online. Detailed advice for travel to specific destinations is available from the Centers for Disease Control and Prevention (CDC) at www.cdc.gov/travel/destinations/list. Recommendations for administration of vaccines as part of routine adult immunization are discussed in a separate issue.

Routine annual vaccination against influenza A and B viruses is recommended for everyone ≥6 months old. Recommendations for the current season for specific patient populations are listed in Tables 2 and 4.

The US Advisory Committee on Immunization Practices (ACIP) recommends routine use of the following vaccines in adults residing in the US: influenza, tetanus/diphtheria alone (Td) and in combination with acellular pertussis (Tdap), measles/mumps/rubella (MMR), varicella (VAR), herpes zoster (RZV; ZVL), human papillomavirus (HPV), and pneumococcal conjugate (PCV13) and polysaccharide (PPSV23) vaccines. For adults with certain medical conditions or occupational, behavioral, or other risk factors, hepatitis A (HepA), hepatitis B (HepB), meningococcal (MenACWY; MenB), and Haemophilus influenzae type b (Hib) vaccines are also recommended. Recommendations for vaccination against seasonal influenza and vaccination of travelers are reviewed separately.

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.

Routine annual vaccination against influenza A and B viruses is recommended for everyone ≥6 months old without a specific contraindication.

Annual vaccination against influenza A and B viruses is recommended for everyone ≥6 months old without a specific contraindication.

The FDA has approved Fluad (Seqirus), an adjuvanted trivalent seasonal influenza vaccine, for immunization of adults ≥65 years old. It will become available later this year for use during the 2016-2017 influenza season. Fluad is the second influenza vaccine to be approved in the US specifically for older adults; Fluzone High-Dose was the first. Fluad has been available in other countries for many years.

Annual vaccination against influenza A and B viruses is recommended for everyone ≥6 months old without a specific contraindication.

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.

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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Patients planning to travel to other countries should be up to date on routine immunizations and, depending on their destination, duration of travel, and planned activities, may also need to receive certain travel-specific vaccines. Common travel vaccines are listed in Table 2. More detailed advice for travelers is available from the Centers for Disease Control and Prevention (CDC) at www.cdc.gov/travel. Guidelines for routine adult immunization are discussed in a separate issue.

Annual vaccination against influenza A and B viruses has been shown to decrease influenza illness and its complications.

Annual vaccination against influenza A and B viruses has been shown to decrease influenza illness and its complications. Several new vaccines are available for the current season.

Two new trivalent influenza vaccines, Flucelvax (Novartis) and Flublok (Protein Sciences), will soon be available for prevention of seasonal influenza in adults ≥18 years old (Flucelvax) and 18-49 years old (Flublok). Unlike other available influenza vaccines, neither vaccine is produced in eggs, removing any concern regarding use in egg-allergic patients. Avoiding the use of eggs should allow for faster production of these 2 new vaccines, which could be especially beneficial during a pandemic.

Flucelvax is prepared in a similar manner to other influenza vaccines, but the influenza virus is grown in canine kidney cell culture instead of chicken eggs. In an unpublished study summarized in the package insert comparing Flucelvax with placebo in more than 11,000 patients during the 2007-2008 season, the new vaccine was effective in preventing about 84% of cases of influenza due to matching strains and was about 70% effective when non-matching strains were included.

Flublok is produced without use of influenza virus or chicken eggs; a gene that encodes for hemagglutinin antigen (HA) is introduced into baculovirus, a virus that infects insect cells, and the replicating baculovirus produces large amounts of HA. In a study in about 4,600 adults conducted during one influenza season, Flublok was about 45% effective compared to placebo in preventing culture-confirmed influenza despite a significant antigenic mismatch between the vaccine and circulating viruses (96% of circulating strains did not match the vaccine). It was 75% effective in preventing illness caused by matching strains.1

Both Flublok and Flucelvax provide protection against the same strains as the other vaccines available for the 2012-2013 influenza season.2

1. JJ Treanor et al. Protective efficacy of a trivalent recombinant hemagglutinin protein vaccine (FluBlok) against influenza in healthy adults: a randomized, placebo-controlled trial. Vaccine 2011; 29:7733.

2. Influenza vaccine 2012-2013. Med Lett Drugs Ther 2012; 54:77.

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Annual vaccination against influenza A and B viruses is the most effective method of preventing influenza and has been shown to decrease influenza illness and its complications. A new vaccine is available for the current season. Chemoprophylaxis and treatment of influenza was discussed in an earlier issue.

Vaccines recommended for routine use in US adults are reviewed here. Vaccines for travel have been reviewed separately.

Live-attenuated vaccines are generally contraindicated during pregnancy; inactivated vaccines can be given if indicated. A more detailed review of routine immunizations for adults will be available in the December issue of Treatment Guidelines from The Medical Letter.

Annual vaccination against influenza A and B viruses is the most effective method of preventing influenza and has been shown to decrease influenza illness and complications. For the current season, a new inactivated intradermal vaccine (Fluzone Intradermal) has been FDA-approved for use in adults 18-64 years old. An upcoming issue will review chemoprophylaxis and treatment of influenza.

Annual vaccination against influenza A and B viruses is the most effective method of preventing influenza. An upcoming issue of The Medical Letter will review drugs for chemoprophylaxis and treatment of influenza.

The FDA has licensed 4 new monovalent vaccines for prevention of respiratory illness caused by a new influenza A H1N1 virus that appears to be derived from a swine strain. The 5th vaccine should be licensed soon. All of these vaccines are expected to become available in October. An intranasal formulation is expected in the first week of October.

Two separate influenza vaccines will be available this season: the usual seasonal trivalent vaccine and a monovalent vaccine (not yet licensed by the FDA) directed at the novel H1N1 virus currently causing pandemic infection. The next issue of the Medical Letter will review the pandemic H1N1 vaccine.

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.

Annual immunization against influenza A and B is the most effective method of preventing infection and has been shown to reduce associated complications.

Since the publication of our article on influenza vaccine (October 9, 2006), a fourth inactivated vaccine (FluLaval - GlaxoSmithKline) has been approved by the FDA for use in people ≥18 years old. It is sold in 5-mL multi-dose vials. Each 0.5-mL intramuscular dose contains 25 mcg of mercury.

Annual immunization against influenza A and B is the most effective method of preventing infection and has been shown to reduce associated complications.

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.

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.

Production problems in some plants have delayed the availability of this year's influenza vaccine and may limit the total supply. These problems appear to be confined to the USA; no shortage is anticipated in Canada

A new trivalent influenza vaccine for intramuscular use is available for the 1999-2000 influenza season.

Patients planning to travel to other countries often ask pysicians for advice about immunizations and prevention of diarrhea and malaria. Legal requirements for entry and epidemiological conditions in different countries vary from time to time, often unpredictably, but some reasonable recommendations can be made.

A new trivalent influenza vaccine for intramuscular use is available for the 1998-1999 influenza season (Morbid Mortal Weekly Rep, 47, RR-6, May 1, 1998). Last year's vaccine was less effective than usual because of the appearance of a new variant (A/Sydney/5/97) after selection of the vaccine antigens (Morbid Mortal Weekly Rep, 47:196, 1998). Antigens in the current vaccine are A/Beijing/262/95-like (H1N1); A/Sydney/5/97-like (H3N2), and B/Harbin/07/94, antigenically equivalent to B/Beijing/184/93. Both H1N1 and the H3N2 antigens are new this year. A highly publicized live attenuated influenza vaccine given by nasal spray (FluMist) has not yet been approved by the FDA and will not be available in the USA for use in the current influenza season (RB Belshe et al, N Engl J Med, 338:1405, 1998).

A new trivalent influenza vaccine for intramuscular use is available for the 1997-1998 influenza season (Morbid Mortal Weekly Rep, 46 RR-9, April 25, 1997). Antigens in the current vaccine are A/johannesburg/82/96, antigenically equivalent to A/Bayern/07/95 (H1N1); A/Nanchang/933/95, antigenically equivalent to A/Wuhan/359/95 (H3N2); and B/Harbin/07/94, antigenically equivalent to B/Beijing/184/93. Only the H1N1 antigen is new this year. A highly publicized nasal spray flu vaccine still has not been approved by the FDA and will not be available in the USA for use in the current influenza season.

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 years delay is being attributed, in part, to the discontinuation 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 (MMWR Morb Mortal Wkly Rep, 50 RR-4:5, April 30, 2001).

A new trivalent influenza vaccine is available for the 1995-1996 influenza season. Influenza vaccine, made from inactivated virus grown in eggs, is recommended especially for elderly and high-risk patients, their household contacts and health-care personnel who may come in contact with such patients (Morbid Mortal Weekly Rep, 44, RR-3, April 21, 1995). Antigens in the current vaccine are derived from A/Texas/36/91/ (H1N1), A/Johannesburg and B/Harbin antigens are new this year.

Tacrolimus (Prograf - Fujisawa), previously called FK506 (Medical Letter, 33:94, 1991), has been approved by the US Food and Drug Administration for primary prevention of organ rejection in patients receiving liver transplants. The drug has also been used as rescue therapy for organ graft rejection unresponsive to cyclosporine (Sandimmune) and other immunosuppressive drugs.

Masoprocol cream 10% (meso-nordihydroguiaretic acid, Actinex - Reed and Carnrick) is now available in the USA for topical treatment of actinic keratoses.

A new trivalent influenza vaccine is available for the 1993-1994 influenza season. Vaccination may be even more important than usual this year because of the appearance late in last year's flu season of a new antigenic variant, which was associated with an increase in deaths (Morbid Mortal Weekly Rep, 42:385, May 28, 1993). Influenza vaccine is recommended especially for the elderly and high-risk patients, their household contacts, and health-care personnel who may come in contact with such patients (Morbid Mortal Weekly Rep, 42,RR-6, May 14, 1993).

A new trivalent influenza vaccine is now available for the 1991-1992 influenza season (Morbid Mortal Weekly Rep, 40, RR-6:1, May 24, 1991). Vaccination is recommended especially for elderly and high-risk patients, their household contacts, and health-care personnel who may come in contact with such patients. Antigens in the current vaccine are derived from A/Taiwan/1/86 (H1N1), A/Beijing/353/89 (H3N2), and B/Panama/45/90 are new this year.