Objective: To provide updated interim guidance on the use of antiviral agents for treatment and chemoprophylaxis of novel influenza (H1N1) virus infection, and assist clinicians in prioritizing use of antivirals for treatment or chemoprophylaxis of patients at higher risk for influenza-related complications. Additional revisions to these recommendations for antiviral treatment should be expected as the epidemiology and clinical presentation of novel influenza A (H1N1) virus infection is better understood. This guidance can be adapted according to local epidemiologic data and antiviral supply considerations.
High-risk groups: A person who is at high-risk for complications of novel influenza (H1N1) virus infection is defined as the same for seasonal influenza at this time. As more epidemiologic and clinical data become available, these risk groups might be revised.
- Children younger than 5 years old. The risk for severe complications from seasonal influenza is highest among children younger than 2 years old.
- Adults 65 years of age and older.
- Persons with the following conditions:
- Chronic pulmonary (including asthma), cardiovascular (except hypertension), renal, hepatic, hematological (including sickle cell disease), neurologic, neuromuscular, or metabolic disorders (including diabetes mellitus);
- Immunosuppression, including that caused by medications or by HIV;
- Pregnant women;
- Persons younger than 19 years of age who are receiving long-term aspirin therapy;
- Residents of nursing homes and other chronic-care facilities.
Transmission: Transmission of novel influenza A (H1N1) is being studied as part of the ongoing outbreak investigation, but limited data available indicate that this virus is likely transmitted in ways similar to other influenza viruses. Seasonal human influenza viruses are thought to be transmitted between persons primarily through large-particle respiratory droplet transmission (e.g., when an infected person coughs or sneezes near a susceptible person). Transmission via these large-particle droplets requires close contact between source and recipient persons because droplets do not remain suspended in the air and generally travel only a short distance (<>
Close contact, for the purposes of this document, is defined as having cared for or lived with a person who is a confirmed, probable or suspected case of novel influenza A (H1N1), or having been in a setting where there was a high likelihood of contact with respiratory droplets and/or body fluids of such a person. Examples of close contact include kissing or embracing, sharing eating or drinking utensils, physical examination, or any other contact between persons likely to result in exposure to respiratory droplets. Close contact typically does not include activities such as walking by an infected person or sitting across from a symptomatic patient in a waiting room or office.
Special Considerations for Children
Aspirin or aspirin-containing products (e.g. bismuth subsalicylate – Pepto Bismol) should not be administered to any confirmed or suspected ill case of novel influenza H1N1 virus infection aged 18 years old and younger due to the risk of Reye syndrome. For relief of fever, other anti-pyretic medications such as acetaminophen or non- steroidal anti-inflammatory drugs are recommended.
Children younger than 4 years of age should not be given over-the-counter cold medications without first speaking with a healthcare provider.
This novel (H1N1) influenza virus is sensitive (susceptible) to the neuraminidase inhibitor antiviral medications, zanamivir and oseltamivir. It is resistant to the adamantane antiviral medications, amantadine and rimantadine.
Antiviral Treatment for Novel (H1N1) Influenza
For antiviral treatment of novel influenza (H1N1) virus infection, either oseltamivir or zanamivir are recommended. Recommendations for use of antivirals may change as data on antiviral effectiveness, clinical spectrum of illness, adverse events from antiviral use, and antiviral susceptibility data become available.
Clinical judgment is an important factor in treatment decisions. Persons with suspected novel H1N1 influenza who present with an uncomplicated febrile illness typically do not require treatment unless they are at higher risk for influenza complications, and in areas with limited antiviral mediation availability, local public health authorities might provide additional guidance about prioritizing treatment within groups at higher risk for infection.
Treatment is recommended for:
- All hospitalized patients with confirmed, probable or suspected novel influenza (H1N1).
- Patients who are at higher risk for seasonal influenza complications (see above).
If a patient is not in a high-risk group or is not hospitalized, healthcare providers should use clinical judgment to guide treatment decisions, and when evaluating children should be aware that the risk for severe complications from seasonal influenza among children younger than 5 years old is highest among children younger than 2 years old. Many patients who have had novel influenza (H1N1) virus infection, but who are not in a high-risk group have had a self-limited respiratory illness similar to typical seasonal influenza. For most of these patients, the benefits of using antivirals may be modest. Therefore, testing, treatment and chemoprophylaxis efforts should be directed primarily at persons who are hospitalized or at higher risk for influenza complications.
Once the decision to administer antiviral treatment is made, treatment with zanamivir or oseltamivir should be initiated as soon as possible after the onset of symptoms. Evidence for benefits from antiviral treatment in studies of seasonal influenza is strongest when treatment is started within 48 hours of illness onset. However, some studies of oseltamivir treatment of hospitalized patients with seasonal influenza have indicated benefit, including reductions in mortality or duration of hospitalization even for patients whose treatment was started more than 48 hours after illness onset. Recommended duration of treatment is five days. Antiviral doses recommended for treatment of novel H1N1 influenza virus infection in adults or children 1 year of age or older are the same as those recommended for seasonal influenza .
Oseltamivir use for children <1>
Note: Areas that continue to have seasonal influenza activity, especially those with circulation of oseltamivir-resistant seasonal human influenza A (H1N1) viruses, might prefer to use either zanamivir or a combination of oseltamivir and rimantadine or amantadine to provide adequate empiric treatment or chemoprophylaxis for patients who might have seasonal human influenza A (H1N1) virus infection.
Antiviral Chemoprophylaxis for Novel (H1N1) Influenza
Post exposure antiviral chemoprophylaxis with either oseltamivir or zanamivir can be considered for the following:
- Close contacts of cases (confirmed, probable, or suspected) who are at high-risk for complications of influenza
- Health care personnel, public health workers, or first responders who haves had a recognized, unprotected close contact exposure to a person with novel (H1N1) influenza virus infection (confirmed, probable, or suspected) during that person’s infectious period. Information on appropriate personal protective equipment is available at: Interim Guidance for Infection Control for Care of Patients with Confirmed or Suspected Swine Influenza A (H1N1) Virus Infection in a Healthcare Setting and might be updated frequently as additional information on transmission becomes available.
Pre-exposure antiviral chemoprophylaxis should only be used in limited circumstances, and in consultation with local medical or public health authorities. Certain persons at ongoing occupational risk for exposure who are also at higher risk for complications of influenza (e.g., health care personnel, public health workers, or first responders who are working in communities with influenza A H1N1 outbreaks) should carefully follow guidelines for appropriate personal protective equipment or consider temporary reassignment.
Antiviral Use for Control of Novel H1N1 Influenza Outbreaks
Use of antiviral drugs for treatment and chemoprophylaxis of influenza has been a cornerstone for the control of seasonal influenza outbreaks in nursing homes and other long term care facilities.
At this time, no outbreaks of novel influenza A (H1N1) have been reported in such settings. However, if such outbreaks were to occur, it is recommended that ill patients be treated with oseltamivir or zanamivir and that chemoprophylaxis with either oseltamivir or zanamivir be started as early as possible to reduce the spread of the virus as is recommended for seasonal influenza outbreaks in such settings.
Chemoprophylaxis should be administered to all non-ill residents and should continue for a minimum of 2 weeks. If surveillance indicates that new cases continue to occur, chemoprophylaxis should be continued until approximately 7 days after illness onset in the last patient. In addition to antiviral medications, other outbreak-control measures include appropriate infection control, establishing cohorts of patients with confirmed or suspected influenza, restricting staff movement between wards or buildings, and restricting contact between ill staff or visitors and patients, and active surveillance for new cases. Medical directors of long-term care facilities should review their plans for outbreak control of influenza.
In addition to use in nursing homes, antiviral chemoprophylaxis also can be considered for controlling influenza outbreaks in other closed or semiclosed settings (e.g., correctional facilities, or other settings in which persons live in close proximity.
| Table 1. Antiviral medication dosing recommendations for treatment or chemoprophylaxis of novel influenza A (H1N1) infection. | |||
| Agent, group | Treatment | Chemoprophylaxis | |
| Oseltamivir | |||
| Adults | 75-mg capsule twice per day for 5 days | 75-mg capsule once per day | |
| Children ≥ 12 months | 15 kg or less | 60 mg per day divided into 2 doses | 30 mg once per day |
| 15-23 kg | 90 mg per day divided into 2 doses | 45 mg once per day | |
| 24-40 kg | 120 mg per day divided into 2 doses | 60 mg once per day | |
| >40 kg | 150 mg per day divided into 2 doses | 75 mg once per day | |
| Zanamivir | |||
| Adults | Two 5-mg inhalations (10 mg total) twice per day | Two 5-mg inhalations (10 mg total) once per day | |
| Children | Two 5-mg inhalations (10 mg total) twice per day (age, 7 years or older) | Two 5-mg inhalations (10 mg total) once per day (age, 5 years or older) | |
