Interim Recommendations for Influenza Vaccination and Post-exposure Chemoprophylaxis to Prevent Influenza Virus Infection in People Being Actively Monitored for Potential Ebola Virus Exposure

Background

Active monitoring of people with potential Ebola virus exposure

Using CDC’s previously published Interim U.S. Guidance for Monitoring and Movement of Persons with Potential Ebola Virus Exposure, public health authorities in the states are responsible for the active monitoring of people with potential Ebola virus exposure until 21 days after the last potential exposure to ensure that, if these individuals become ill, they are identified as soon as possible after symptom onset so they can be rapidly isolated and evaluated. According to these current guidelines, when people under active monitoring because of potential risk of exposure to Ebola virus develop fever, they meet the case definition for a person under investigation (PUI) for Ebola and should be medically evaluated for the cause of fever, while remaining in isolation. This diagnostic evaluation will likely include testing of respiratory specimens for influenza. Preventing influenza transmission in this population may reduce the number of people requiring evaluation as a PUI.

Preventing influenza after exposure

Household contacts of people with suspected or confirmed influenza virus infection are at high risk for secondary influenza virus infection. Annual influenza vaccination is the best way to prevent influenza virus infection and is recommended for all people ≥6 months of age. For some people, influenza antiviral chemoprophylaxis could help prevent household influenza transmission. CDC has guidance on available antiviral agents and their use for influenza chemoprophylaxis. Good hand hygiene and cough etiquette are also important to prevent the transmission of influenza viruses.

Recommendations:

1. Public health authorities responsible for active monitoring of people with potential Ebola virus exposure should, at their first contact, inquire about influenza vaccination status. People who have not already been vaccinated during the current influenza season should be offered influenza vaccination.
2. During influenza season, public health authorities responsible for active monitoring of people with potential Ebola virus exposure should consider including assessment of household exposure to influenza, including household members with newly diagnosed influenza or fever and symptoms consistent with influenza, in their routine monitoring procedures.
3. People under active monitoring who have had close, prolonged exposure to a household contact with suspected or confirmed influenza may be offered counseling of the risks and benefits and post-exposure influenza antiviral chemoprophylaxis.
4. Antiviral chemoprophylaxis, with either oral oseltamivir or inhaled zanamivir (see Table 1 for dosing recommendations), should be considered only if it can be initiated within 48 hours of the first exposure to a household contact ill with suspected or confirmed influenza and continued for 7 days after the last known exposure. Antiviral chemoprophylaxis should not be initiated if the time of exposure is uncertain.
5. People under active monitoring who are taking influenza antiviral chemoprophylaxis should also be assessed on a daily basis for adherence to chemoprophylaxis.
6. During influenza season, public health authorities responsible for active monitoring of people with potential Ebola virus exposure should remind these persons and their families to use good hand hygiene and cough etiquette to reduce the risk of acquiring a respiratory virus infection such as influenza.

Influenza vaccination of persons with potential Ebola virus exposure

CDC recommends that all people aged 6 months and older be vaccinated annually. There are many influenza vaccine formulations available for the 2014-2015 season, including trivalent vaccines (which provide protection against two influenza A viruses [an H1N1 and an H3N2] and one influenza B virus), and quadrivalent vaccines (which provide protection against two influenza A viruses and two influenza B viruses). Different influenza vaccines have different approved age indications. An age-appropriate formulation of influenza vaccine should always be used. In addition to age specifications, some influenza vaccine types are not recommended for use in some populations (for example, pregnant women or people with specific allergies or certain chronic medical conditions). Package inserts should be consulted for approved age indications, information on contraindications and precautions, and complete information regarding vaccine components. In addition, the Advisory Committee on Immunization Practices (ACIP), Influenza Vaccine Recommendations, 2014-15 should be consulted for guidance in selecting an appropriate influenza vaccine formulation and for information on vaccination of specific populations.

At the first contact with a person under active monitoring because of potential Ebola virus exposure, public health officials should inquire about influenza vaccination history for the current season. If the person has not been vaccinated during the current season, vaccination should be offered as soon as possible, since delaying vaccination until the end of the 21-day monitoring period would result in a significant delay in protection. Influenza vaccination should also be offered to any unvaccinated members of the household, to limit the likelihood of exposure to influenza through household contacts.

The following caveats should be considered:

• Antibody development after vaccination takes about two weeks in adults and can take longer in children, depending on their age and vaccination history. Therefore, protection offered by vaccination may not occur until near the end of the 21-day active monitoring period.
• Administration of influenza vaccine may be associated with fever and symptoms such as myalgias, and arthralgias – signs and symptoms that are also associated with Ebola. These symptoms are generally uncommon among adults after influenza vaccination and usually resolve within 1 to 2 days.
• Because influenza antiviral medications interfere with the replication of influenza viruses, these drugs may reduce the effectiveness of live attenuated influenza vaccine (the intranasally-administered vaccine). If influenza antiviral medications are administered within 48 hours before or within 2 weeks after vaccination, the efficacy of the live attenuated vaccine may be compromised. Inactivated influenza vaccine should therefore be considered in persons who are taking antiviral chemoprophylaxis and for persons who may need influenza antiviral medications.

Key messages when offering antiviral chemoprophylaxis for influenza

• Annual influenza vaccination is the best way to prevent influenza because vaccination can be given well before influenza virus exposures occur and can provide safe and effective immunity throughout the influenza season, assuming a good match between circulating and vaccine virus strains.
• When given as post-exposure chemoprophylaxis, influenza antiviral medications are approximately 70% to 90% effective in preventing influenza in a household setting when the prevalence of antiviral-resistant viruses is low and when administered promptly, and are useful adjuncts to influenza vaccination.
• To be effective as post-exposure chemoprophylaxis, influenza antiviral medication must be started soon after exposure, taken each day for the duration of potential exposure to a person with influenza virus infection, and continued for 7 days after the last known exposure.
• Influenza antiviral chemoprophylaxis should generally not be given if more than 48 hours have elapsed since the first exposure to an infectious person. Influenza antiviral agents used for chemoprophylaxis have potential side effects (see attached package inserts).
  • Oseltamivir [PDF – 30 pages]: mild to moderate nausea and vomiting (can be reduced by taking with food)
  • Zanamivir [PDF – 18 pages]: bronchospasm (not recommended for persons with underlying airway disease such as asthma or chronic obstructive pulmonary disease)

Table 1: Recommended dosage and duration of antiviral medications for chemoprophylaxis of influenza

* Oral oseltamivir is approved by the FDA for chemoprophylaxis in persons 1 year of age and older. Although not part of the FDA-approved indications, use of oral oseltamivir for chemoprophylaxis in infants 3 months to 1 year of age is recommended by the CDC and the American Academy of Pediatrics. Because of limited data in infants <3 months of age, the use of oseltamivir for chemoprophylaxis is not recommended for children in this age group, unless the situation is judged to be critical. Inhaled zanamivir is FDA-approved and recommended for use in children 5 years of age or older.