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Swine influenza

The Emergency Committee, established in compliance with the International Health Regulations (2005), held its second meeting on 27 April 2009.

he Committee considered available data on confirmed outbreaks of A/H1N1 swine influenza in the United States of America, Mexico, and Canada. The Committee also considered reports of possible spread to additional countries.

On the advice of the Committee, the WHO Director-General decided on the following.

• The Director-General has raised the level of influenza pandemic alert from the current phase 3 to phase 4.
  
  The change to a higher phase of pandemic alert indicates that the likelihood of a pandemic has increased, but not that a pandemic is inevitable.
  
  As further information becomes available, WHO may decide to either revert to phase 3 or raise the level of alert to another phase.
  
  This decision was based primarily on epidemiological data demonstrating human-to-human transmission and the ability of the virus to cause community-level outbreaks.
  
  
• Given the widespread presence of the virus, the Director-General considered that containment of the outbreak is not feasible. The current focus should be on mitigation measures.
  
  
• The Director-General recommended not to close borders and not to restrict international travel. It was considered prudent for people who are ill to delay international travel and for people developing symptoms following international travel to seek medical attention.
  
  
• The Director-General considered that production of seasonal influenza vaccine should continue at this time, subject to re-evaluation as the situation evolves. WHO will facilitate the process needed to develop a vaccine effective against A(H1N1) virus.
  
  
• The Director-General stressed that all measures should conform with the purpose and scope of the International Health Regulations.

printable version Current WHO phase of pandemic alert Current phase of alert in the WHO global influenza preparedness plan Pandemic preparedness In the 2009 revision of the phase descriptions, WHO has retained the use of a six-phased approach for easy incorporation of new recommendations and approaches into existing national preparedness and response plans. The grouping and description of pandemic phases have been revised to make them easier to understand, more precise, and based upon observable phenomena. Phases 1–3 correlate with preparedness, including capacity development and response planning activities, while Phases 4–6 clearly signal the need for response and mitigation efforts. Furthermore, periods after the first pandemic wave are elaborated to facilitate post pandemic recovery activities. The current WHO phase of pandemic alert is 4. In nature, influenza viruses circulate continuously among animals, especially birds. Even though such viruses might theoretically develop into pandemic viruses, in Phase 1 no viruses circulating among animals have been reported to cause infections in humans. In Phase 2 an animal influenza virus circulating among domesticated or wild animals is known to have caused infection in humans, and is therefore considered a potential pandemic threat. In Phase 3, an animal or human-animal influenza reassortant virus has caused sporadic cases or small clusters of disease in people, but has not resulted in human-to-human transmission sufficient to sustain community-level outbreaks. Limited human-to-human transmission may occur under some circumstances, for example, when there is close contact between an infected person and an unprotected caregiver. However, limited transmission under such restricted circumstances does not indicate that the virus has gained the level of transmissibility among humans necessary to cause a pandemic. Phase 4 is characterized by verified human-to-human transmission of an animal or human-animal influenza reassortant virus able to cause “community-level outbreaks.” The ability to cause sustained disease outbreaks in a community marks a significant upwards shift in the risk for a pandemic. Any country that suspects or has verified such an event should urgently consult with WHO so that the situation can be jointly assessed and a decision made by the affected country if implementation of a rapid pandemic containment operation is warranted. Phase 4 indicates a significant increase in risk of a pandemic but does not necessarily mean that a pandemic is a forgone conclusion. Phase 5 is characterized by human-to-human spread of the virus into at least two countries in one WHO region. While most countries will not be affected at this stage, the declaration of Phase 5 is a strong signal that a pandemic is imminent and that the time to finalize the organization, communication, and implementation of the planned mitigation measures is short. Phase 6, the pandemic phase, is characterized by community level outbreaks in at least one other country in a different WHO region in addition to the criteria defined in Phase 5. Designation of this phase will indicate that a global pandemic is under way. During the post-peak period, pandemic disease levels in most countries with adequate surveillance will have dropped below peak observed levels. The post-peak period signifies that pandemic activity appears to be decreasing; however, it is uncertain if additional waves will occur and countries will need to be prepared for a second wave. Previous pandemics have been characterized by waves of activity spread over months. Once the level of disease activity drops, a critical communications task will be to balance this information with the possibility of another wave. Pandemic waves can be separated by months and an immediate “at-ease” signal may be premature. In the post-pandemic period, influenza disease activity will have returned to levels normally seen for seasonal influenza. It is expected that the pandemic virus will behave as a seasonal influenza A virus. At this stage, it is important to maintain surveillance and update pandemic preparedness and response plans accordingly. An intensive phase of recovery and evaluation may be required.

Swine influenza frequently asked questions

• What is swine influenza?
• What are the implications for human health?
• Where have human cases occurred?
• How do people become infected?
• Is it safe to eat pork and pork products?
• Which countries have been affected by outbreaks in pigs?
• What about the pandemic risk?
• Is there a human vaccine to protect from swine influenza?
• What drugs are available for treatment?
• What should I do if I am in regular contact with pigs?
• How can I protect myself from getting swine influenza from infected people?
• What should I do if I think I have swine influenza?

What is swine influenza?

Swine influenza, or “swine flu”, is a highly contagious acute respiratory disease of pigs, caused by one of several swine influenza A viruses. Morbidity tends to be high and mortality low (1-4%). The virus is spread among pigs by aerosols, direct and indirect contact, and asymptomatic carrier pigs. Outbreaks in pigs occur year round, with an increased incidence in the fall and winter in temperate zones. Many countries routinely vaccinate swine populations against swine influenza.

Swine influenza viruses are most commonly of the H1N1 subtype, but other subtypes are also circulating in pigs (e.g., H1N2, H3N1, H3N2). Pigs can also be infected with avian influenza viruses and human seasonal influenza viruses as well as swine influenza viruses. The H3N2 swine virus was thought to have been originally introduced into pigs by humans. Sometimes pigs can be infected with more than one virus type at a time, which can allow the genes from these viruses to mix. This can result in an influenza virus containing genes from a number of sources, called a "reassortant" virus. Although swine influenza viruses are normally species specific and only infect pigs, they do sometimes cross the species barrier to cause disease in humans.

What are the implications for human health?

Outbreaks and sporadic human infection with swine influenza have been occasionally reported. Generally clinical symptoms are similar to seasonal influenza but reported clinical presentation ranges broadly from asymptomatic infection to severe pneumonia resulting in death.

Since typical clinical presentation of swine influenza infection in humans resembles seasonal influenza and other acute upper respiratory tract infections, most of the cases have been detected by chance through seasonal influenza surveillance. Mild or asymptomatic cases may have escaped from recognition; therefore the true extent of this disease among humans is unknown.

Where have human cases occurred?

Since the implementation of IHR(2005)¹ in 2007, WHO has been notified of swine influenza cases from the United States and Spain.

How do people become infected?

People usually get swine influenza from infected pigs, however, some human cases lack contact history with pigs or environments where pigs have been located. Human-to-human transmission has occurred in some instances but was limited to close contacts and closed groups of people.

Is it safe to eat pork and pork products?

Yes. 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. The swine influenza virus is killed by cooking temperatures of 160°F/70°C, corresponding to the general guidance for the preparation of pork and other meat.

Which countries have been affected by outbreaks in pigs?

Swine influenza is not notifiable to international animal health authorities (OIE, www.oie.int), therefore its international distribution in animals is not well known. The disease is considered endemic in the United States. Outbreaks in pigs are also known to have occurred in North America, South America, Europe (including the UK, Sweden, and Italy), Africa (Kenya), and in parts of eastern Asia including China and Japan.

What about the pandemic risk?

It is likely that most of people, especially those who do not have regular contact with pigs, do not have immunity to swine influenza viruses that can prevent the virus infection. If a swine virus establishes efficient human-to human transmission, it can cause an influenza pandemic. The impact of a pandemic caused by such a virus is difficult to predict: it depends on virulence of the virus, existing immunity among people, cross protection by antibodies acquired from seasonal influenza infection and host factors.

Is there a human vaccine to protect from swine influenza?

There are no vaccines that contain the current swine influenza virus causing illness in humans. It is not known whether current human seasonal influenza vaccines can provide any protection. Influenza viruses change very quickly. It is important to develop a vaccine against the currently circulating virus strain for it to provide maximum protection to the vaccinated people. This is why WHO needs access to as many viruses as possible in order to select the most appropriate candidate vaccine virus.

What drugs are available for treatment?

There are two classes of such medicines, 1) adamantanes (amantadine and remantadine), and 2) inhibitors of influenza neuraminidase (oseltamivir and zanamivir).

Most of the previously reported swine influenza cases recovered fully from the disease without requiring medical attention and without antiviral medicines.

Some influenza viruses develop resistance to the antiviral medicines, limiting the effectiveness of treatment. The viruses obtained from the recent human cases with swine influenza in the United States are sensitive to oselatmivir and zanamivir but resistant to amantadine and remantadine.

Information is insufficient to make recommendation on the use of the antivirals in treatment of swine influenza virus infection. Clinicians have to make decisions based on the clinical and epidemiological assessment and harms and benefit of the treatment of the patient². For the ongoing outbreak of the swine influenza infection in the United States and Mexico, the national and the local authorities are recommending to use oseltamivir or zanamivir for treatment of the disease based on the virus’s susceptibility profile.

What should I do if I am in regular contact with pigs?

Even though there is no clear indication that the current human cases with swine influenza infection are related to recent or ongoing influenza-like disease events in pigs, it would be advisable to minimize contact with sick pigs and report such animals to relevant animal health authorities.

Most people are infected through prolonged, close contact with infected pigs. Good hygiene practices are essential in all contact with animals and are especially important during slaughter and post-slaughter handling to prevent exposure to disease agents. Sick animals or animals that died from disease should not be undergoing slaughtering procedures. Follow further advice from relevant national authorities.

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. The swine influenza virus is killed by cooking temperatures of 160°F/70°C corresponding to the general guidance for the preparation of pork and other meat.

How can I protect myself from getting swine influenza from infected people?

In the past, human infection with swine influenza was generally mild but is known to have caused severe illness such as pneumonia For the current outbreaks in the United States and Mexico however, the clinical pictures have been different. None of the confirmed cases in the United States have had the severe form of the disease and the patients recovered from illness without requiring medical care. In Mexico, some patients reportedly had the severe form of the disease.

To protect yourself, practice general preventive measures for influenza:

• Avoid close contact with people who appear unwell and who have fever and cough.
• Wash your hands with soap and water frequently and thoroughly.
• Practice good health habits including adequate sleep, eating nutritious food, and keeping physically active.

If there is an ill person at home:

• Try to provide the ill person a separate section in the house. If this is not possible, keep the patient at least 1 meter in distance from others.
• Cover mouth and nose when caring for the ill person. Masks can be bought commercially or made using the readily available materials as long as they are disposed of or cleaned properly.
• Wash your hands with soap and water thoroughly after each contact with the ill person.
• Try to improve the air flow in the area where the ill person stays. Use doors and windows to take advantage of breezes.
• Keep the environment clean with readily available household cleaning agents.

If you are living in a country where swine influenza has caused disease in humans, follow additional advice from national and local health authorities.

What should I do if I think I have swine influenza?

If you feel unwell, have high fever, cough and/or sore throat:

• Stay at home and keep away from work, school or crowds as much as possible.
• Rest and take plenty of fluids.
• Cover your mouth and nose with disposable tissues when coughing and sneezing and dispose of the used tissues properly.
• Wash your hands with soap and water frequently and thoroughly, especially after coughing or sneezing.
• Inform family and friends about your illness and seek help for household chores that require contact with other people such as shopping.

If you need medical attention:

• Contact your doctor or healthcare provider before travelling to see them and report your symptoms. Explain why you think you have swine influenza (for example, if you have recently travelled to a country where there is a swine influenza outbreak in humans). Follow the advice given to you for care.
• If it is not possible to contact your healthcare provider in advance, communicate your suspicion of having swine influenza immediately upon arrival at the healthcare facility.
• Take care to cover your nose and mouth during travel.

RELATED LINKS

- ¹ International Health Regulations (2005)
- ² Benefits and harms of influenza-specific antivirals

http://news.bbc.co.uk/2/hi/americas/8021547.stm