Symptoms of swine flu are similar to most influenza infections: fever (100 F or greater), cough, nasal secretions, fatigue, and headache, with fatigue being reported in most infected individuals. Some patients may also get a sore throat, rash, body aches, headaches, chills, nausea, vomiting, and diarrhea. In Mexico, many of the initial patients infected with H1N1 influenza were young adults, which made some investigators speculate that a strong immune response, as seen in young people, may cause some collateral tissue damage.The incubation period from exposure to first symptoms is about one to four days, with an average of two days. The symptoms last about one to two weeks and can last longer if the person has a severe infection.
Some patients develop severe respiratory symptoms and need respiratory support (such as a ventilator to breathe for the patient). Patients can get pneumonia (bacterial secondary infection) if the viral infection persists, and some can develop seizures. Death often occurs from secondary bacterial infection of the lungs; appropriate antibiotics need to be used in these patients. The usual mortality (death) rate for typical influenza A is about 0.1%, while the 1918 “Spanish flu” epidemic had an estimated mortality rate ranging from 2%-20%. Swine (H1N1) flu in Mexico had about 160 deaths and about 2,500 confirmed cases, which would correspond to a mortality rate of about 6%, but these initial data were revised and the mortality rate worldwide was estimated to be much lower. Fortunately, the mortality rate of H1N1 remained low and similar to that of the conventional flu (average conventional flu mortality rate is about 36,000 per year; projected H1N1 flu mortality rate was 90,000 per year in the U.S. as determined by the president’s advisory committee, but it never approached that high number).
Fortunately, although H1N1 developed into a pandemic (worldwide) flu strain, the mortality rate in the U.S. and many other countries only approximated the usual numbers of flu deaths worldwide. Speculation about why the mortality rate remained much lower than predicted includes increased public awareness and action that produced an increase in hygiene (especially hand washing), a fairly rapid development of a new vaccine, and patient self-isolation if symptoms developed.
Can swine flu be prevented with a vaccine?
The CDC recommends for the 2014-2015 flu season that everyone 6 months old and older should get a flu shot to prevent or reduce the chance of getting the flu. The best way to prevent novel H1N1 swine flu is vaccination. The 2014 CDC recommendations that apply to H1N1, H3N2, and other flu viruses are almost identical to those above-mentioned recommendations for patients at risk when vaccine doses are limited and are as follows:
- Are aged 6 months through 4 years (59 months)
- Are aged 50 years and older
- Have chronic pulmonary (including asthma), cardiovascular (except hypertension), renal, hepatic, neurologic, hematologic, or metabolic disorders (including diabetes mellitus)
- Are immunosuppressed (including immunosuppression caused by medications or by human immunodeficiency virus)
- Are or will be pregnant during the influenza season
- Are aged 6 months through 18 years and receiving long-term aspirin therapy and who therefore might be at risk for experiencing Reye’s syndrome after influenza virus infection
- Are residents of nursing homes and other chronic-care facilities
- Are American Indians/Alaska Natives
- Are morbidly obese (body-mass index is 40 or greater)
- Are health-care personnel
- Are household contacts and caregivers of children aged younger than 5 years and adults aged 50 years and older, with particular emphasis on vaccinating contacts of children aged younger than 6 months
- Are household contacts and caregivers of people with medical conditions that put them at higher risk for severe complications from influenza
- As in previous recommendations, all children aged 6 months to 8 years of age who receive a seasonal influenza vaccine for the first time should receive two doses. Children who received only one dose of a seasonal influenza vaccine in the first influenza season should receive two doses rather than one in the following influenza season.
- A newly approved inactivated trivalent vaccine containing 60 mcg of hemagglutinin antigen per influenza vaccine virus strain (Fluzone High-Dose [Sanofi Pasteur]) is an alternative inactivated vaccine for people 65 years of age and older.
The CDC occasionally makes changes and updates its information on vaccines and other recommendations about the current flu pandemic. The CDC states, “for the most accurate health information, visit http://www.cdc.gov or call 1-800-CDC-INFO, 24/7.” Caregivers should check the vaccine package inserts for more detailed information on the vaccines when they become available.