H1N1 Influenza (Swine Flu) Follow-up

Updated: Nov 23, 2016
  • Author: Michael Stuart Bronze, MD; Chief Editor: Russell W Steele, MD  more...
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Follow-up

Deterrence/Prevention

Vaccination campaign

The 2009 influenza A (H1N1) monovalent vaccine was released in mid October. The immunization series consisted of 2 doses for children younger than 10 years, consisting of an initial dose and a booster to be administered several weeks later. Adults and children 10 years and older received a single dose. Targeted populations recommended to receive the 2009 H1N1 vaccine included pregnant women, household contacts and caregivers of children younger than 6 months, healthcare and emergency medical services personnel, children aged 6 months to 18 years, young adults aged 19-24 years, and persons aged 25 through 64 years with conditions associated with higher risk of medical complications from influenza. [41, 42]

A separate seasonal influenza vaccine was needed for the 2009/2010 influenza season because it was too late to incorporate the new strain into the regular influenza vaccine already in production. Now H1N1 is a component of the trivalent and quadrivalent influenza vaccines.

A 2011 CDC analysis reaffirms the importance of vaccinating pregnant women regardless of trimester and prompt treatment with a neuraminidase inhibitor (ie, within 2 d of symptom onset) if influenza occurs during pregnancy. [34]

There are only a limited number of studies that describe the safety of giving influenza vaccine to pregnant women. A 2012 study in Denmark found no evidence of an increased risk of fetal death associated with exposure to an adjuvanted pandemic A/H1N1 2009 influenza vaccine during pregnancy. [43]

Community precautions

The CDC recommends the following actions when human infection with H1N1 influenza (swine flu) is confirmed in a community [1] :

  • Household contacts who are not ill
    • Remain home at the earliest sign of illness.
    • Minimize contact in the community to the extent possible.
    • Designate a single household family member as caregiver for the patient to minimize interactions with asymptomatic persons.
  • School dismissal and childcare facility closure
    • Strong consideration should be given to close schools upon a confirmed case of H1N1 flu or a suspected case epidemiologically linked to a confirmed case.
    • Decisions regarding broader school dismissal within these communities should be left to local authorities, taking into account the extent of influenzalike illness within the community.
    • Cancelation of all school or childcare related gatherings should also be announced.
    • Encourage parents and students to avoid congregating outside of the school if school is canceled.
    • Duration of schools and childcare facilities closings should be evaluated on an ongoing basis depending on epidemiological findings.
    • Consultation with local or state health departments is essential for guidance concerning when to reopen schools. If no additional confirmed or suspected cases are identified among students (or school-based personnel) for a period of 7 days, schools may consider reopening.
    • Schools and childcare facilities in unaffected areas should begin preparation for possible school closure.
  • Social distancing
    • Large gatherings linked to settings or institutions with laboratory-confirmed cases should be canceled (eg, sporting events or concerts linked to a school with cases); other large gatherings in the community may not need to be canceled at this time.
    • Additional social distancing measures are currently not recommended.
    • Persons with underlying medical conditions who are at high risk for complications of influenza should consider avoiding large gatherings.

Preventive measures for health care personnel

The CDC has issued interim recommendations for controlling the spread of H1N1 influenza in health care settings. [44] Recommended measures for care of patients with suspected or confirmed H1N1 influenza include the following:

  • Place patients in a single-patient room with the door kept closed. An airborne-infection isolation room with negative-pressure air handling can be used, if available. Air can be exhausted directly outside or can be recirculated after filtration by a high efficiency particulate air (HEPA) filter.
  • Suctioning, bronchoscopy, or intubation should be performed in a procedure room with negative-pressure air handling.
  • Patients should wear a surgical mask when outside their room.
  • Encourage patients to wash their hands frequently and to follow respiratory hygiene practices. Cups and other utensils used by the ill person should be washed with soap and water before use by other persons.
  • Standard, droplet, and contact precautions should be used for all patient care activities and maintained for 7 days after illness onset or until symptoms have resolved.
  • Health care personnel should wash their hands with soap and water or use hand sanitizer immediately after removing gloves and other equipment and after any contact with respiratory secretions.
  • Personnel providing care to or collecting clinical specimens from patients should wear disposable nonsterile gloves, gowns, and eye protection (eg, goggles) to prevent conjunctival exposure.
  • As per previous recommendations regarding mask and respirator use during influenza pandemics, personnel engaged in aerosol-generating activities (eg, collection of clinical specimens, endotracheal intubation, nebulizer treatment, bronchoscopy) and/or resuscitation involving emergency intubation or cardiac pulmonary resuscitation should wear a fit-tested disposable N95 respirator.
  • Pending clarification of transmission patterns for the 2009 H1N1 influenza A (swine flu) virus, personnel providing direct patient care for suspected or confirmed cases should wear a fit-tested disposable N95 respirator when entering the patient's room.

2009 H1N1 vaccine efficacy and adverse effects

Zhu et al (2009) assessed the safety and immunogenicity of the 2009 H1N1 vaccine in a randomized clinical trial in populations ranging in age from 3-77 years. In the study, 2200 individuals received one dose, 2103 (95.6%) of whom received a second dose or placebo. A single 15-mcg dose of hemagglutinin antigen without alum adjuvant induced a typically protective immune response in most participants aged 12-60 years. Severe adverse effects were not observed. Mild injection-site reactions were reported in up to 16% of individuals. [45]

Communication from the US FDA Commissioner, Margaret Hamburg, summarized safety data after 11.3 million doses of intranasal and 34.9 million doses of injectable vaccine were distributed. Analysis of 3783 reports of adverse events was reported to the vaccine adverse event reporting system (VAERS) through November 24, 2009, based on 438,376 people vaccinated. The vast majority (94%) of adverse events described were classified as nonserious (eg, soreness at site of injection). No cases of Guillain-Barré syndrome have been reported. As of December 30, 2009, nearly 100 million doses of H1N1 vaccine had been distributed. [46]

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Prognosis

A review of medical records from the 2009 US pandemic found hospitalized patients with pandemic H1N1 and pneumonia were at risk for severe outcomes including ARDS, sepsis, and death. However, patients often received delayed antiviral treatment (>2 days after illness onset). Patients with H1N1 and pneumonia should receive early and aggressive treatment with antibiotics and influenza antiviral agents. [47]

In a multicenter study in Britain consisting of over 1,500 patients, independent predictors of severe outcome included age 55-64 years, certain chronic lung diseases, underlying neurological disease, obesity, delayed admission (≥5 days after illness onset), pneumonia, and others. [48]

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Patient Education

See the patient education article Swine Flu.

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