What is swine flu

Swine flu was the popular name for flu caused by a relatively new type of flu virus responsible for a global flu outbreak (or pandemic) in 2009-10. It’s now just a normal type of seasonal flu and is included in the annual flu vaccine.

The scientific name for the swine flu virus is A/H1N1pdm09 – sometimes shortened to “H1N1”.

Swine flu (swine influenza) is a respiratory disease of pigs caused by type A influenza viruses that regularly cause outbreaks of influenza in pigs. Influenza viruses that commonly circulate in swine are called “swine influenza viruses” or “swine flu viruses.” Like human influenza viruses, there are different subtypes and strains of swine influenza viruses. The main swine influenza viruses circulating in U.S. pigs in recent years have been, swine triple reassortant (tr) H1N1 influenza virus, trH3N2 virus, and trH1N2 virus ¹. Swine flu viruses can cause high levels of illness in swine herds, but usually cause few deaths. Common signs in sick pigs include fever, depression, coughing (barking), discharge from the nose or eyes, sneezing, breathing difficulties, eye redness or inflammation, and going off feed. However, influenza-infected pigs also may not appear ill or be only mildly ill. Swine influenza viruses may circulate among swine throughout the year, but most outbreaks occur during the late fall and winter months similar to outbreaks of seasonal influenza in humans.

Swine flu viruses do not normally infect humans. However, sporadic human infections with influenza viruses that normally circulate in swine and not people have occurred. When this happens, these viruses are called “variant viruses.” They also can be denoted by adding the letter “v” to the end of the virus subtype designation. Human infections with H1N1v, H3N2v and H1N2v viruses have been detected in the United States. Most commonly, human infections with variant viruses have occurred in people exposed to infected pigs (e.g., children near pigs at a fair or workers in the swine industry). In addition, there have been documented cases of multiple persons becoming sick after exposure to one or more sick pigs. Also, cases of limited person-to-person spread of variant viruses have occurred.

Influenza viruses that infect pigs may be different from human influenza viruses. Thus, influenza vaccines made against human influenza viruses are generally not expected to protect people from influenza viruses that normally circulate in pigs. In addition, because pigs are susceptible to avian, human and swine influenza viruses, they potentially may be infected with influenza viruses from different species (e.g., ducks and humans) at the same time. If this happens, it is possible for the genes of these viruses to mix and create a new virus. This type of major change in the influenza A viruses is known as antigenic shift. If this new virus causes illness in people and can be transmitted easily from person-to-person, an influenza pandemic can occur. This is what happened in 2009 when an influenza A H1N1 virus with swine, avian and human genes emerged in the spring of 2009 and caused the first pandemic in more than 40 years.

“Swine flu” pandemic 2009-10

The virus was first identified in Mexico in April 2009. It became known as swine flu because it’s similar to flu viruses that affect pigs.

It spread rapidly from country to country because it was a new type of flu virus that few young people were immune to.

Overall, the outbreak wasn’t as serious as originally predicted, largely because many older people were already immune to it. Most cases in the US were relatively mild – although serious cases still occurred.

The relatively small number of cases resulting in serious illness and death were mostly in younger adults and children – particularly those with underlying health problems – and pregnant women.

On August 10 2010, the World Health Organization (WHO) declared the pandemic officially over.

How are variant influenza viruses spread?

Influenza viruses can be directly transmitted from pigs to people and from people to pigs. These infections have most commonly been reported after close proximity to infected pigs, such as in pig barns and livestock exhibits housing pigs at fairs. Infected pig cough or sneeze and droplets with influenza virus in them can spread through the air. If these droplets land in your nose or mouth, or are inhaled, you can be infected. There also is some evidence that you might get infected by touching a surface with virus on it and then touching your mouth or nose. A third way to possibly get infected is to inhale droplets or dust containing influenza virus. Scientists aren’t really sure which of these ways of spread is the most common.

Human-to-human transmission of variant flu viruses also has occurred, though this method of spread has been limited. This kind of transmission is thought to occur in the same way that seasonal flu transmits in people, which is mainly through coughing or sneezing by people who are infected. People also may become infected by touching something with flu viruses on it and then touching their mouth or nose. It’s important to note that in most cases, variant flu viruses have not shown the ability to spread easily and sustainably from person to person.

“Swine flu” now

Influenza viruses that normally circulate in pigs are called “variant” viruses when they are found in people. Influenza A H3N2 variant viruses (also known as “H3N2v” viruses) with the matrix (M) gene from the 2009 H1N1 pandemic virus were first detected in people in July 2011. The viruses were first identified in U.S. pigs in 2010. In 2011, 12 cases of H3N2v infection were detected in the United States (Indiana, Iowa, Maine, Pennsylvania, and West Virginia). In 2012, 309 cases of H3N2v infection across 12 states were detected. In 2013, 19 cases of H3N2v across five states were detected ².

Human infections with H1N1v, H3N2v and H1N2v viruses have been detected in the United States. Most commonly, human infections with variant viruses occur in people with exposure to infected pigs (e.g., children near pigs at a fair or workers in the swine industry). This is thought to happen mainly when an infected pig coughs or sneezes and droplets with influenza virus in them spread through the air. If these droplets land in your nose or mouth, or are inhaled, you can be infected. There also is some evidence that you might get infected by touching something that has virus on it and then touching your own mouth or nose. A third way to possibly get infected is to inhale particles containing influenza virus. Scientists aren’t really sure which of these ways of spread is the most common.

Swine influenza has not been shown to be transmissible to people through eating properly handled and prepared pork (pig meat) or other products derived from pigs.

Influenza H1N1 complications

Influenza complications include:

• Worsening of chronic conditions, such as heart disease and asthma
• Pneumonia
• Neurological signs and symptoms, ranging from confusion to seizures
• Respiratory failure

H1N1 swine flu causes

Influenza viruses infect the cells lining your nose, throat and lungs. The virus enters your body when you inhale contaminated droplets or transfer live virus from a contaminated surface to your eyes, nose or mouth.

You can’t catch swine flu from eating pork.

Risk factors for H1N1 swine flu

If you’ve traveled to an area where many people are affected by swine flu (H1N1 flu), you may have been exposed to the virus, particularly if you spent time in large crowds.

Swine farmers and veterinarians have the highest risk of true swine flu because of their exposure to pigs.

H1N1 flu prevention

The Centers for Disease Control and Prevention recommends flu vaccination for all people older than 6 months of age. An H1N1 virus is one component of the seasonal flu shot for 2014-15. The flu shot also protects against two or three other influenza viruses that are expected to be the most common during the flu season.

The vaccine will be available as an injection or a nasal spray. The nasal spray is approved for use in healthy people 2 through 49 years of age who are not pregnant. The nasal spray isn’t recommended for people who are older than 50, younger than 2, pregnant or allergic to eggs, or people who have asthma or a compromised immune system, or those who use aspirin therapy.

These measures also help prevent swine flu (H1N1 flu) and limit its spread:

• Stay home if you’re sick. If you have swine flu (H1N1 flu), you can give it to others. Stay home for at least 24 hours after your fever is gone.
• Wash your hands thoroughly and frequently. Use soap and water, or if they’re unavailable, use an alcohol-based hand sanitizer.
• Contain your coughs and sneezes. Cover your mouth and nose when you sneeze or cough. To avoid contaminating your hands, cough or sneeze into a tissue or the inner crook of your elbow.
• Avoid contact. Stay away from crowds if possible. And if you’re at high risk of complications from the flu — for example, you’re younger than 5 or you’re 65 or older, you’re pregnant, or you have a chronic medical condition such as asthma — consider avoiding swine barns at seasonal fairs and elsewhere.
• Reduce exposure within your household. If a member of your household has swine flu, designate only one household member to be responsible for the ill person’s personal care.

Pigs can be infected with their own influenza viruses (called swine influenza) that are usually different from human flu viruses. While rare, influenza can spread from pigs to people and from people to pigs. When people get swine flu viruses, it’s usually after contact with pigs. This has happened in different settings, including fairs. The Centers for Disease Control and Prevention ³ recommends people take the following actions to help prevent the spread of flu between pigs and people.

CDC Recommendations for People with High Risk Factors:

• Anyone who is at high risk of serious flu complications planning to attend a setting where pigs will be present should avoid pigs and swine barns.
• People who are at high risk of serious flu complications include children younger than 5 years, people 65 years and older, pregnant women, and people with certain long-term health conditions (like asthma and other lung disease, diabetes, heart disease, weakened immune systems, and neurological or neurodevelopmental conditions).

CDC Recommendations for People Not at High Risk:

• Don’t take food or drink into pig areas; don’t eat, drink or put anything in your mouth in pig areas.
• Don’t take toys, pacifiers, cups, baby bottles, strollers, or similar items into pig areas.
• Avoid close contact with pigs that look or act ill.
• Take protective measures if you must come in contact with pigs that are known or suspected to be sick. This includes minimizing contact with pigs and wearing personal protective equipment like protective clothing, gloves and masks that cover your mouth and nose when contact is required.
• Wash your hands often with soap and running water before and after exposure to pigs. If soap and water are not available, use an alcohol-based hand rub.
• To further reduce the risk of infection, minimize contact with pigs in the pig barn and arenas.
• Watch your pig (if you have one) for illness. Call a veterinarian if you suspect illness.
• Avoid contact with pigs if you have flu symptoms. Wait to have contact with pigs until 7 days after your illness started or until you have been without fever for 24 hours without the use of fever-reducing medications, whichever is longer. If you must have contact with pigs while you are sick, take the protective actions listed above.

People with high risk factors who develop flu symptoms should call a health care provider. Tell them about your high risk factor and any exposure to pigs or swine barns you’ve had recently. Human seasonal flu vaccine will not protect against commonly circulating swine influenza viruses, but prescription influenza antiviral drugs can treat infections with these viruses in people.

Flu Vaccination

Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP)—United States, 2017-18 ⁴

• Routine annual influenza vaccination is recommended for all persons aged ≥6 months who do not have contraindications.
• Emphasis should be placed on vaccination of high-risk groups and their contacts and caregivers (no hierarchy is implied by order of listing):
  • Children aged 6-59 months;
  • Adults aged ≥50 years;
  • Persons with chronic pulmonary (including asthma), cardiovascular (except isolated hypertension), renal, hepatic, neurologic, hematologic, or metabolic disorders (including diabetes mellitus);
  • Persons who are immunocompromised due to any cause, (including medications or HIV infection);
  • Women who are or will be pregnant during the influenza season;
  • Children and adolescents (aged 6 months through 18 years) receiving aspirin- or salicylate-containing medications and who might be at risk for Reye syndrome;
  • Residents of nursing homes and other long-term care facilities;
  • American Indians/Alaska Natives;
  • Persons who are extremely obese (BMI ≥40); and
• Caregivers and contacts of those at risk:
  • Health care personnel in inpatient and outpatient care settings, medical emergency-response workers, employees of nursing home and long-term care facilities who have contact with patients or residents, and students in these professions who will have contact with patients;
  • Household contacts and caregivers of children aged ≤59 months (i.e., <5 years), particularly contacts of children aged <6 months, and adults aged ≥50 years; and
  • Household contacts and caregivers of persons who are in one of the high-risk categories listed.

Influenza Vaccine Composition for 2017-2018

• All 2017-18 influenza vaccines licensed in the United States will contain hemagglutinin (HA) derived from influenza viruses antigenically similar to those recommended by FDA.
• 2017–18 trivalent vaccines:
  • an A/Michigan/45/2015 (H1N1)pdm09–like virus;
  • an A/Hong Kong/ 4801/2014 (H3N2)–like virus; and
  • a B/Brisbane/60/2008–like virus (Victoria lineage).
• 2017–18 quadrivalent vaccines:
  • the same three HA antigens as trivalent vaccines, plus
  • a B/Phuket/3073/2013–like virus (Yamagata lineage).

Timing of Vaccination

• Optimally, vaccination should occur before onset of influenza activity in the community.
  • Vaccination should be offered by end of October, if possible.
  • Vaccination should be offered as long as influenza viruses are circulating and unexpired vaccine is available.
• Children aged 6 months through 8 years who require 2 doses should receive their first dose as soon as possible after vaccine becomes available, and the second dose ≥4 weeks later.

Guidance for Use in Specific Situations

Volume per Dose for Children and Adults

• Children aged 6 through 35 months may receive either:
  • 0.5mL FluLaval Quadrivalent (IIV4) intramuscularly, or
  • 0.25mL Fluzone Quadrivalent (IIV4) intramuscularly.
  • Note that dose volume differs for these two brands. Care should be taken to administer the correct dose.
• Children aged 3 through 17 years may receive 0.5mL intramuscularly of an age-appropriate IIV formulation.
• Adults aged 18 years and older may receive 0.5mL intramuscularly of an age-appropriate IIV or RIV.
  • Alternatively, adults aged 18 through 64 years may receive 0.1mL intradermally of Fluzone Intradermal Quadrivalent (administered using the included delivery device).
• If a smaller intramuscular dose (e.g., 0.25mL) is administered to an adult, an additional dose should be administered to provide a full 0.5mL dose. If the error is discovered later (after the recipient has left the vaccination setting), a full 0.5mL dose should be administered as soon as the recipient can return.

Number of Doses for Children Aged 6 Months through 8 Years

• Determine the number of doses needed for this age group as follows:
  • Has the child received ≥2 doses of trivalent or quadrivalent influenza vaccine before July 1, 2017? (*Note: Doses need not have been given during same or consecutive seasons)
    • If Yes: 1 dose of 2017-18 influenza vaccine
    • If No/Don’t Know: 2 doses of 2017-18 influenza vaccine (administered ≥4 weeks apart)

Pregnant Women

• All women who are pregnant or who might be pregnant during the influenza season should receive influenza vaccine.
  • Any licensed, recommended, and age-appropriate, influenza vaccine may be used.
  • LAIV is not recommended for use in any population for 2017-18. Providers who use it should note that LAIV should not be used during pregnancy.
• Influenza vaccine can be administered at any time during pregnancy, before and during the influenza season.

Adults Aged ≥65 years

• May receive any age-appropriate IIV (standard- or high-dose, trivalent or quadrivalent, adjuvanted or unadjuvanted) or RIV.
• High-dose IIV3 exhibited superior efficacy over comparator standard-dose IIV3 in a large randomized trial, and may provide better protection than standard dose IIV3 for this age group.
• However, vaccination should not be delayed to find a particular product if an appropriate one is available.

Immunocompromised Persons

• LAIV is not recommended for use in any population for 2017-18. Providers who use it should note that LAIV should not be used for immunocompromised persons.
• Immunocompromised persons should receive an age-appropriate IIV or RIV
• Immune response to vaccines might be blunted in immunocompromised persons.
• Timing of vaccination might be a consideration (e.g., in some period before or after an immunocompromising intervention).
• The Infectious Diseases Society of America (IDSA) has published detailed guidance for the selection and timing of vaccines for persons with specific immunocompromising conditions.

High-Risk Persons and their Caregivers and Contacts

• High-risk persons and their caregivers and contacts (including those of immunosuppressed persons) may receive any age-appropriate IIV or RIV
• LAIV is not recommended for use in any population for 2017-18. Providers who use it should note that health care personnel or hospital visitors who receive LAIV should avoid providing care for severely immunosuppressed persons (those requiring a protected environment) for 7 days after vaccination.

Persons with a History of Egg Allergy

• Persons who are able to eat lightly cooked egg (e.g., scrambled egg) without reaction are unlikely to be egg-allergic.
• Persons who have experienced only hives after exposure to egg should receive any licensed, recommended, age-appropriate influenza vaccine (i.e., IIV or RIV).
• Persons reporting symptoms other than hives, such as angioedema, respiratory distress, lightheadedness, or recurrent emesis; or who required epinephrine or another emergency medical intervention, may also receive any licensed and recommended influenza vaccine that is otherwise appropriate.
  • Additionally, for these persons, vaccine should be administered in an inpatient or outpatient medical setting and supervised by a health care provider who is able to recognize and manage severe allergic conditions.
• A previous severe allergic reaction to influenza vaccine, regardless of the component suspected of causing the reaction, is a contraindication to future receipt of the vaccine.

Vaccination Issues for Travelers

• Travelers who wish to reduce the risk for influenza infection should consider influenza vaccination, preferably ≥2 weeks before departure.
• Persons at high risk for complications of influenza who were not vaccinated during the preceding fall or winter should consider receiving influenza vaccine before departure, if they plan to travel to the tropics, with organized tourist groups or on cruise ships, or to the Southern Hemisphere during April–September.
• Influenza vaccine formulated for the Southern Hemisphere might differ in viral composition from Northern Hemisphere vaccine.
• Southern Hemisphere influenza vaccines are generally not available in the U.S.

Vaccination and Influenza Antiviral Medications

• IIV and RIV may be administered to persons receiving influenza antiviral medications for treatment or chemoprophylaxis.
• LAIV is not recommended for use in any population for 2017-18.  If used, note that influenza antivirals may reduce the effectiveness of LAIV, if administered within 48 hours before to 2 weeks after vaccination.

Swine flu symptoms

People who have been infected with variant viruses have had symptoms similar to the symptoms of regular human seasonal influenza. These include fever, lethargy, lack of appetite and coughing. Some people also have reported runny nose, sore throat, eye irritation, nausea, vomiting and diarrhea.

H1N1 flu signs and symptoms in humans are similar to those of other flu strains:

• a sudden fever – a temperature of 38 °C (100.4 °F) or above (but not always)
• aching body
• feeling tired or exhausted
• dry, chesty cough
• sore throat
• runny or stuffy nose
• watery, red eyes
• headache
• difficulty sleeping
• fatigue
• loss of appetite
• diarrhea or tummy pain
• nausea and vomiting

The symptoms are similar for children, but they can also get pain in their ear and appear less active.

H1N1 flu symptoms develop about one to three days after you’re exposed to the virus.

How can human infections with variant influenza H1N1 virus be diagnosed?

To diagnose variant influenza A virus infection, a respiratory specimen would generally need to be collected within the first 4 to 5 days of illness (when an infected person is most likely to be shedding virus). However, some people, especially children, may shed virus longer. Since the 2009 H1N1 pandemic, state health departments have the ability to test for novel (non-human) influenza viruses. However, if a variant influenza virus is suspected, it is sent to CDC for further testing.

Swine flu treatment

Most cases of flu, including H1N1 flu, require only symptom relief. If you have a chronic respiratory disease, your doctor may prescribe additional medications to help relieve your symptoms.

There are three different antiviral drugs that are recommended for use in the United States for the treatment of influenza: oseltamivir (Tamiflu), peramivir (Rapivab®) and zanamivir (Relenza).

The antiviral drugs oseltamivir (Tamiflu) and zanamivir (Relenza) are sometimes prescribed within the first day or two of symptoms to reduce the severity of your symptoms, and possibly the risk of complications. But, flu viruses can develop resistance to these drugs.

Generic oseltamivir and Tamiflu® are available as a pill or liquid suspension and are FDA approved for early treatment of flu in people 14 days old and older. Relenza® is a powder that is inhaled and approved for early treatment of flu in people 7 years of age and older. (Note: Relenza® is not recommended for people with breathing problems like asthma or COPD.) Rapivab® is given intravenously by a health care provider and is approved for early treatment of flu in people 2 years of age and older.

To treat the flu, oseltamivir and zanamivir are usually prescribed to be taken twice daily for 5 days, although people hospitalized with the flu may need antiviral treatment for longer than 5 days. Peramivir is given one time intravenously over a period of 15 to 30 minutes.

To make development of resistance less likely and maintain supplies of these drugs for those who need them most, antivirals are reserved for people at high risk of complications.

High-risk groups are those who:

• Are in a hospital, nursing home or other long-term care facility
• Are younger than 5 years of age, particularly children younger than 2 years
• Are 65 years and older
• Are pregnant or within two weeks of delivery, including women who have had pregnancy loss
• Are younger than 19 years of age and are receiving long-term aspirin therapy, because of an increased risk of developing Reye’s syndrome, a rare but
• potentially fatal disease that can occur when using aspirin during a viral illness
• Are morbidly obese, defined as having a body mass index above 40
• Have certain chronic medical conditions, including asthma, emphysema, heart disease, diabetes, neuromuscular disease, or kidney, liver or blood disease
• Are immunosuppressed due to certain medications or HIV
• Are American Indians or Native Alaskans

When used for treatment, antiviral drugs can lessen symptoms and shorten the time you are sick by 1 or 2 days. However, starting them later can still be helpful, especially if the sick person has a high-risk health condition or is very sick from the flu (for example, hospitalized patients). Follow your doctor’s instructions for taking these drugs.

Antiviral drugs can prevent serious flu complications, like pneumonia. For people at high risk of serious flu complications, treatment with antiviral drugs can mean the difference between milder or more serious illness possibly resulting in a hospital stay.

The most common reported side effects of antiviral drugs for flu are nausea and vomiting. Other less common side effects also have been reported.

Can children take antiviral drugs?

Yes. Oseltamivir is recommended by the CDC and American Academy of Pediatrics (AAP) for early treatment of flu in people of any age, and for the prevention of flu (i.e., prophylaxis) in people 3 months of age and older. Zanamivir is recommended for early treatment of flu in people 7 years of age and older, and for the prevention of flu in people 5 years of age and older. Peramivir is recommended for early treatment in people 2 years of age and older.

Can pregnant women take antiviral drugs?

Yes. Oral oseltamivir is recommended for treatment of pregnant women with flu because compared to other recommended antiviral medications it has the most studies available to suggest that it is safe and beneficial during pregnancy.

Lifestyle and home remedies

If you develop any type of flu, these measures may help ease your symptoms:

• Drink plenty of liquids. Choose water, juice and warm soups to prevent dehydration.
• Rest. Get more sleep to help your immune system fight infection.
• Consider pain relievers. Use an over-the-counter pain reliever, such as acetaminophen (Tylenol, others) or ibuprofen (Advil, Motrin IB, others), cautiously. Also, use caution when giving aspirin to children or teenagers. Though aspirin is approved for use in children older than age 3, children and teenagers recovering from chickenpox or flu-like symptoms should never take aspirin. This is because aspirin has been linked to Reye’s syndrome, a rare but potentially life-threatening condition, in such children. Remember, pain relievers may make you more comfortable, but they won’t make your symptoms go away faster and may have side effects. Ibuprofen may cause stomach pain, bleeding and ulcers. If taken for a long period or in higher than recommended doses, acetaminophen can be toxic to your liver.

1. Swine Influenza. https://www.cdc.gov/flu/swineflu/[↩]
2. Influenza A (H3N2) Variant Virus. https://www.cdc.gov/flu/swineflu/h3n2v-situation.htm[↩]
3. Take Action to Prevent the Spread of Flu Between Pigs and People. https://www.cdc.gov/flu/swineflu/variant/preventspreadfactsheet.htm[↩]
4. 2017-18 Summary of Recommendations. https://www.cdc.gov/flu/professionals/acip/2017-18summary.htm[↩]