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Frequently asked questions
Answers to media professionals' most common questions and overview of WPRO activities.
THE VIRUS
What is Influenza A (H1N1)?
H1N1 is a newly identified influenza virus now spreading among humans. Its technical name is Influenza A (H1N1).
Why has it been called “swine flu”?
The virus is a genetic re-assortment, or a rearranging, of four different virus strains – two swine strains, one avian and one human. Because it contains two different swine genes, scientists initially described it as a 'swine influenza virus'. However, with the exception of an isolated herd in Canada, this virus has not yet been found in pigs. As the term 'swine flu' was causing some confusion and there is no evidence that this virus is circulating in pigs, WHO decided to change its name to the more scientific terms influenza A(H1N1).
What is a re-assortment?
When animals or humans are infected with two different flu viruses at the same time, those viruses can swap genes, thus generating a third type of virus. This process is called reassortment and usually produces new viruses that can be a mix of different genes. H1N1 is known as a “reassortant” as it is composed of swine, avian and human genes. This particular combination has not previously been seen in humans or swine, and the precise origin of the reassortment is uncertain.
What are the symptoms of influenza A(H1N1)?
As with seasonal flu, early symptoms include fever, coughing, headache, muscle and joint pain, sore throat and runny nose. Vomiting and diarrhoea can also occur. Some infected people may show no or only slight symptoms.
Can H1N1 be fatal?
H1N1 has not caused a high number of fatalities, as most sufferers have recovered. However, deaths have been reported in two groups of people – people with underlying medical conditions and also, unusually, young previously healthy adults between the ages of 25 and 44. The major cause of death from H1N1 has been respiratory failure and major organ failure, following severe respiratory distress.
How is H1N1 different from seasonal flu?
Although it is still very early in the outbreak and data are still limited there appear to be four major differences between influenza A(H1N1) and seasonal influenza:
- Influenza A(H1N1) appears to be more transmissible between humans than seasonal influenza. With seasonal influenza we usually see around 10% of the population being infected, with influenza A(H1N1) we are have seen that around 30% of the population in affected areas have become infected
- Seasonal influenza usually infects people of all ages. So far only a very small number of cases of influenza A(H1N1) have been reported in people over the age of 50, the vast majority of cases are in people under the age of 50 and those with underlying health conditions.
- Seasonal influenza tends to cause severe disease only in the very young and the elderly. Influenza A(H1N1) in contrast has caused severe illness in otherwise healthy people between the ages of 25 and 44 and those with underlying health conditions.
- Unlike seasonal flu, between 40% and 50% of H1N1 sufferers have experienced diarrhoea.
EXPOSURE AND TRANSMISSION
Who is most at risk of infection?
H1N1 has been most prevalent in the young adult population, in contrast to seasonal flu to which the young and elderly are usually the most vulnerable. This should not be taken to mean that the young and elderly may not be vulnerable as well to becoming infected. Others also at higher risk are those with underlying health conditions eg asthma, diabetes, heart conditions, chronic disease and pregnant women.
How is it contracted?
It can be caught just like a normal flu; by breathing in air contaminated with infected droplets from a sneeze or cough by an infected person, or by touching infected hands or surfaces and then touching your eyes, nose or mouth.
Are we detecting all cases?
In areas where a lot of cases are being reported, testing is focusing on those people with more severe illness. This means that it is likely that reported figures are, even now, an underestimate of the true picture. In some high burden countries it is likely that at some point in the near future testing will be restricted further to priority cases only. Authorities will test only a small number of people and provide estimates and situation descriptions instead of exact case counts. In addition, based on early data from Mexico it seems likely that some people will be infected but not show any symptoms. If this is confirmed in other studies, it means that it will not be possible to detect all cases.
How long can an infected person spread H1N1 flu to others?
People with A(H1N1) influenza should be considered potentially contagious as long as they are symptomatic and possible for up to 7 days following illness onset. Children, especially younger children, might potentially be contagious for longer periods.
Is there a risk from drinking water?
The chance of catching H1N1 from drinking water is considered to be very low. Tap water treated by conventional disinfection processes is unlikely to pose any risk for transmission of influenza viruses. It isn’t yet known whether H1N1 can be eradicated by water treatment such as chlorination, but as chlorination has been shown to kill seasonal and avian flu it is thought likely that H1N1 would be similarly affected.
Should people avoid travel?
WHO is not recommending travel restrictions as experience has shown that stopping travel does not stop the spread of a virus. People who are ill should delay travel plans. Returning travelers who become ill should contact their health care provider.
Could it combine with H5N1?
It is theorectically possible that if a human or a pig were to be infected with influenza A(H1N1) and influenza A(H5N1) at the same time that a third virus could be produced through reassortment. There is currently no evidence that it has or is likely to occur but authorities in areas where influenza A(H5N1) is known to be circulating in poultry and where humans cases have occurred are increasing their vigilance. If you are sick with influenza you should avoid close contact with people and with animals.
Is transmission from humans to pigs possible?
Transmission from humans to pigs is thought possible. On May 2, the Canadian Food Inspection Agency announced that a herd of swine infected with H1N1 probably caught it from a worker recently returned from Mexico showing flu symptoms. The pigs fell ill shortly afterward. Further investigations taking place into risks of back-transmission to swine.
What are the chances of a second wave of infection?
This virus is a serious threat to global health and continued vigilance is crucial, even though H1N1 hasn’t caused a high number of deaths. It is a new virus and may yet mutate into a more severe strain as it moves among humans and animals. Everyone should remain on maximum alert.
Can H1N1 be contracted by eating pork?
No. Influenza viruses are not known to be transmissible to people through eating processed food products derived from pigs. The cooking process will kill any viruses present in the raw meat, so long the meat is cooked at a core temperature of at least 70°C/158°F. As is always the case, meat from sick pigs or pigs found dead should not be processed or eaten by humans.
TREATMENT
Do antivirals help?
This is currently not known for certain, and WHO is working with public health authorities and clinicians to gather information on how effective antiviral drugs are against H1N1. As this is a new virus, only a small number of people have been treated for it with antivirals. Testing in WHO Collaborating Centres indicate that H1N1 is sensitive to oseltamivir and zanamivir, but resistance to another class of antivirals known as adamantanes.
Are there enough of these antivirals?
At present we don’t know how much we will need, but existing stockpiles are unlikely to meet demand. Therefore, prudent use of antivirals is essential. It is very important that governments and public health authorities work together to boost global antiviral stockpiles. This is vital to protect people from H1N1 and also from future viruses.
What is WHO doing to increase stocks of antivirals?
WHO’s top priority is to galvanize the international community to provide emergency stocks of antivirals to countries most in need. WHO wants antiviral manufacturers to produce more, at more affordable prices, and has approached donors and governments to secure extra resources for poor countries.
What has WHO been told by antiviral manufacturers regarding a scaling up of production?
WHO understands that manufacturers plan to dramatically increase production of antiviral drugs.
Could a resistant strain evolve?
Resistance to antiviral drugs used for influenza can develop. WHO is monitoring antiviral drug resistance to ensure treatments are as effective as possible.
How long before a vaccine is developed?
A vaccine will take around 5 to 6 months to develop. WHO is receiving valuable information daily on the epidemiological pattern, number of people who might be affected, and the seriousness of disease, which will help in vaccine production.
How much vaccine will be needed?
Global vaccine needs are conservatively estimated at between 1 billion and 2 billion doses in first year.
Will developing nations get the vaccine quickly?
It is essential that developing nations get equitable access to a vaccine. WHO is working now to make sure this happens. This could occur through manufacturers donating vaccine to WHO as occurred for avian flu and support from development banks.
THE NATURE OF A PANDEMIC
What exactly does WHO mean by a “pandemic”? Does it mean mass fatalities are likely or inevitable?
A pandemic is a worldwide epidemic of a disease. It does not necessarily mean mass fatalities. A pandemic refers to how far across the globe the disease has spread, rather than its severity, and as such a pandemic can result in a low fatality count. It may start mild and become severe, or vice versa. It may also start mild and stay that way, or start severe and stay severe. It could last between 18 months and two years and come in waves.
What do Pandemic Alert Phases 5 and 6 mean?
Phase 5 means there have been sustained community-level breakouts of the virus in at least two countries in one WHO region. At that point a pandemic is considered imminent. Phase 6 is triggered when a sustained community-level infection is confirmed in a country in second WHO region, at which point WHO considers a pandemic to have started.
How is the current situation different from previous pandemics such as 1918?
Times have changed. Science has progressed and made the world better equipped to counter a pandemic. In 1918, precautions were not as sophisticated as they are now. Now we have continual global surveillance of influenza viruses to ensure early detection of unusual outbreaks. WHO has a network or more than 120 National Influenza Centres in over 90 countries to monitor the spread of influenza. Unusual outbreaks are reported immediately, enabling a timely and efficient response. On the other hand, in some ways the dynamics and interconnections of modern life have made us more vulnerable. Growth in international travel and the increased size of urban conurbations has added to the risk of viruses spreading around the globe faster than in the past.
How has WHO approached the crisis?
An epidemic of this kind is by nature unpredictable. Authorities are trying to understand the nature of the virus, inhibit its spread, and push for ways to quickly find effective antiviral drugs and a vaccine.
INFECTION TRENDS
Why has the death toll been comparatively low to date?
There are signs that H1N1 may be less deadly than originally feared. This should not be taken to mean the worst is over. Although it is the end of the influenza season in the northern hemisphere, it is the start of influenza season in the southern hemisphere and infections may increase in other countries.
Could H1N1 spread faster in Asia during the southern winter?
Flu is usually seasonal, and therefore the virus could spread south into Asia with the onset of the southern winter. While there is no cause for alarm, there is certainly a case for enhanced vigilance to ensure Asia is well-prepared. Concern is warranted, as Asia contains many developing countries and has a younger population who may be more susceptible to the virus.
Could a new, perhaps even more severe, flu virus be created from H1N1 and spread?
H1N1 is a recently discovered virus and it may mutate into a more severe flu strain. Any movement back and forth between humans and pigs and from person to person could increase the risk of mutation, leading to a more severe strain. There is as yet no evidence that this has happened but extreme vigilance is necessary.
How can the world be better prepared next time?
Our past experience with flu epidemics has made the world much better prepared. Still, there is good reason to further bolster our defences. Stockpiles of antiviral drugs should be increased. There is a need for a quicker way of manufacturing vaccines to ensure as many people as possible are vaccinated.