Questions and answers on the pandemic (H1N1) 2009

What is the influenza A(H1N1)v virus?

The present influenza A(H1N1)v virus is a new virus subtype of influenza affecting humans, which contains segments of genes from pig, bird and human influenza viruses in a combination that has never been observed before anywhere in the world. New viruses are often the result of a re-assortment of genes from two other viruses (swap of genes). This A(H1N1)v virus is the result of a combination of two swine influenza viruses that contained genes of avian and human origin.

What is the origin of the 2009 pandemic influenza A(H1N1) virus?

Influenza A viruses are single stranded RNA virus with eight different genetic segments.

The two Mechanisms whereby Pandemic Influenza Originates:

  • when two viruses co-infect the same cell, new viruses can be produced that contain segments from both parental strains (a re-assortment)
  • One genetic segment codes for the haemagglutinine, one for neuraminidase
  • Nine different Hs and 16 different Ns have been identified
  • These decide the naming of the strain: H1N1, H5N1, H7N7, etc.
  • In principle thus 9 x 16 = 144 different strains possible. Most are only avian.
  • Extensive public databases of sequenced influenza viruses already available
  • New virus has been sequenced by
    • sequence alignment,
    • cluster analyses by principal component analysis,
    • phylogenetic tree, we can trace the origin of the virus.
  • Closest relatives to this new strain found in swine
  • Six genetic segments from North America and two from European/Asian swine influenza
  • One North American segment closely related to swine H3N2 isolates from 1998 that had human, swine and avian origin
  • However, the virus has not been reported from pigs, neither in Mexico nor in the US, is this due to:
    • in sufficient surveillance?
    • 'silent’ infection in pigs?
    • very recent re-assortment?

What is the difference between the pandemic (H1N1) 2009 and swine influenza?

The typical swine influenza (swine flu) is an acute viral infection of the respiratory tract in pigs, caused by type A influenza virus. The mortality rate is low in pigs and recovery usually occurs within 7–10 days. Swine-origin influenza infections also occur in wild birds, poultry, horses and humans, but transmission between species is considered a rare event. So far three influenza type A virus subtypes have been found in pigs: H1N1, H1N2 and H3N2.

Zoonotic human infections with swine influenza viruses have been detected occasionally since the late 1950s, usually in persons with direct exposure to pigs (e.g. people working on pig farms, etc.). In Europe, since 1958 a total of 17 cases have been reported. In the US in 1976, an outbreak of swine influenza virus infections in humans was detected among recruits in a military camp in Fort Dix, New Jersey. A link to pigs was presumed but never established. Instead there was limited human-to-human transmission, with over 200 infections resulting in 12 hospitalisations and one death.

In contrast to the swine influenza virus, the new influenza A(H1N1)v virus is capable of human-to-human transmission.

What is the difference between seasonal influenza and the 2009 pandemic?

This table lists the ten characteristics whereby the new pandemic virus differs from the ‘old’ seasonal especially as it appeared in its later years (2000/2001 to 2008/9 season).

There are also a number of similarities such as the family of viruses, that both are human adapted viruses and that they are transmitted in the same way. What is unknown at present is how the ‘new’ seasonal influenza – that which will presumably appear in the autumn and winter of 2010/11 will be the same as or differ from the ‘old’ seasonal influenza.

See Eurosurveillance (Volume 15, Issue 1, 07 January 2010) for discussion: A new decade, a new seasonal influenza: the Council of the European Union Recommendation on seasonal influenza vaccination

 Seasonal Influenza 2000/1 to 2008/92009 Pandemic Influenza
Circulating Influenza VirusesTwo A viruses (H1N1), (H3N2) & some B viruses - blend varied with seasonAlmost exclusively the pandemic (H1N1), a few (H3N2) & increasing numbers of B viruseslatterly
When waves occurredIn season - mostly starting after Christmas in recent yearsStarted out of season with Spring/Summer wave then an early Autumn/Winter wave in Europe
Intensity of transmissionVariable year on year, with local heterogeneity but estimated to be 5 to 15% per annumHard to estimate, local heterogeneity, estimated to be over 15% through serological studies reviewed by WHO and in New Zealand
Setting for transmissionProbably any setting where people come togetherSchools are considered especially important, along with household transmission
Experiencing severe diseaseThose in clinical risk groups and older peopleYoung children, pregnant women and those in clinical risk groups.  About 30% with severe disease were outside risk groups.  Many born before mid-1950s were immune, but those not experienced severe disease. Donaldson et al
Premature DeathsConsidered that around 90% were in those aged 65 years or older Thompson et al

In confirmed reported deaths around 80% were under age 65 years (Reports to ECDC)   

Increase in all-cause deaths in children detected across eight EU countries by Euromomo system

Mortality and Years of Potential Life Lost (YPLL)Few confirmed deaths reported each year in official statistics. Have been estimates of up to 40,000 in a bad year using  statistical methods

Substantial numbers of confirmed deaths announced by EU/EFTA Member States (n = 2900) but recognised to be an underestimate.

Not estimated in any EU member states but estimated in the US

Acute respiratory distress syndromeExtremely rareUncommon but has been recorded in many countries, even in young fit adults. This is partially explained by the tropism of the pandemic virus for epithelial receptors that predominate in the lung alveoli while the previous seasonal viruses bind best to receptors found predominately in the upper airways.
Pathological FindingsViral pneumonia rare but secondary bacterial infections more common in fatal casesFatal viral pneumonias relatively common with alveolar lining cells, including type I and type II pneumocytes the primary infected cells. In fatalities more than 25% also had bacterial infections.
Antiviral resistanceCommon and transmissible oseltamivir resistance in A(H1N1) emerged in season 2007/8 Meijer et alObserved most often following antiviral treatment of susceptible individuals. However to date (July 2010) only transmitting very rarely in certain circumstances. Resistant seasonal A(H1N1) seemingly displaced by the new influenza, at least for now.


What are the symptoms of influenza A(H1N1)v?

Symptoms of influenza A(H1N1)v in humans are usually similar to regular human seasonal influenza symptoms:

  • Fever
  • Respiratory symptoms such as cough or runny nose
  • Sore throat
  • Possibly other symptoms such as
    • Body aches (particularly muscle pain)
    • Headache
    • Chills
    • Fatigue
    • Vomiting or diarrhoea (not typical in seasonal influenza but reported in a substantial number of cases of influenza A(H1N1)v )

In some cases, severe complications could occur even in normally healthy persons who become infected with the virus (see Q17).

How do people become infected with influenza A(H1N1)v?

People become infected with influenza A(H1N1)v in the same way as with seasonal influenza. There are three routes of transmission:

  • airborne: via droplets from an infected person who is sneezing or coughing in a face-to-face situation;
  • direct (skin) contact: by hand, contaminated by an infected droplet, touching the mouth;
  • indirect (skin) contact: through any material (e.g. door handle) contaminated by an infected droplet, touched by the hand that then touches the mouth.

How long is the incubation period? How long can an infected person spread the influenza A (H1N1)v virus to others?

Ongoing investigations suggest that the incubation period is from one to seven days. At the current time, it is believed that this virus has the same properties in terms of spread as seasonal influenza viruses. Based on that, adults who are sick can infect others for approximately five days after symptoms start, and children are infectious for approximately seven days after symptoms start. However, it is prudent to consider someone infectious for the entire time they have symptoms.

Can the influenza A (H1N1)v virus be transmitted to humans by eating pork and pork products?

No. The influenza virus is not transmitted by eating properly handled and cooked pork and pork products. The European Food Safety Authority (EFSA) and ECDC are not aware of any scientific evidence to suggest that influenza viruses can be transmitted to humans through the consumption of meat such as pork and pork products.

Regardless of the present epidemic, longstanding food safety advice is to avoid eating raw meat in order to prevent possible risk of food-borne illness. It is always recommended to follow proper food hygiene practices in kitchens and to wash hands and all surfaces and equipment with soap after handling raw meat. Cooking pork thoroughly (to an internal temperature of 70°C) kills viruses and bacteria.

Can the influenza A(H1N1)v virus be passed back and forth between humans and pigs?

Canadian officials reported on 2 May 2009 that a farm worker infected with the influenza A(H1N1)v virus had passed the virus to pigs in Alberta, Canada, and there have been similar cases in Argentina and Australia. WHO food safety scientists confirmed that there is a risk that the disease could also infect people who work closely with sick pigs on farms or in slaughterhouses. In the past, several cases were documented in which people caught swine flu from contact with infected pigs.

However, health officials repeated that it is safe to eat properly cooked pork as the virus cannot be transmitted by eating properly handled and cooked pork or pork products (see Q6). The main risk of this human-to-animal infection is that a new re-assortant virus could emerge from pigs co-infected by the pandemic virus and by another swine virus. This could lead potentially to a ‘new’ virus with possible increased severity.

Is there a vaccine against influenza A(H1N1)v?

Regulatory authorities have licensed pandemic vaccines in several countries, including Australia, China and the United States. In the European Union, the European Commission has granted authorisation to three vaccines for influenza pandemic (H1N1) 2009, following the positive scientific opinion issued by the Committee for Medicinal Products for Human Use (CHMP) at the European Medicines Agency (EMEA).

The products concerned are Focetria® (Novartis), Pandemrix® (GlaxoSmithKline) and Celvapan® (Baxter). The vaccines are authorised for use in all Member States of the EU and the EEA (Iceland, Liechtenstein and Norway). That should ensure that sufficient vaccines will be available before the start of the flu season and will reduce the risks for illnesses and deaths for European Citizens.

In addition, the National Regulatory Agency in Hungary provided a national licence of a pandemic vaccine produced by the Hungarian manufacturer Omninvest on 29 September 2009 for use in Hungary.

Vaccine production capacity has increased recently, which is a reassuring sign for Europe in terms of potentially having sufficient vaccine available to cover the needs of the population. Eventually the decision of who will get the vaccine is the responsibility of the Member States and individual doctors advising patients.

Is the human seasonal influenza vaccine effective against influenza A(H1N1)v?

There are certain similarities between the usual H1N1 human influenza viruses (covered by the seasonal vaccine) and the influenza A (H1N1)v virus but recent evidence suggests no significant cross-protection.

Can influenza A(H1N1)v be treated?

So far, most human cases of influenza A(H1N1)v are mild and probably most patients will recover by themselves. Current evidence suggests that the influenza A(H1N1)v virus is susceptible to antiviral medications such as neuraminidase inhibitors but resistant to amantadanes. Antivirals could alleviate symptoms and reduce the course of the disease and are essential in the treatment of severe cases.

Can the virus be resistant to antiviral treatment?

Cases of pandemic (H1N1) 2009 that were resistant to the antiviral medicine oseltamivir (Tamiflu®, a neuraminidase inhibitor) were reported in a few countries. So far, these findings appear to be isolated cases and these virus strains are thought to be unfit (i.e. will not transmit from person to person) though this is still under investigation to be confirmed and established. Hence there is no immediate public health impact.

It is too early to predict if oseltamivir-resistant viruses will spread. It is possible that these will remain isolated findings.

The good news is that the oseltamivir-resistant viruses identified are not resistant to zanamivir.

WHO is closely monitoring the situation through its Global Influenza Surveillance Network and other networks and will provide updated information when available.

What is the mortality rates from influenza?

Number of deaths reported from the 2009 influenza A(H1N1) pandemic are sometimes compared to the number of deaths from seasonal influenza. One perspective is that fewer people have died from the 2009 influenza pandemic than from ordinary seasonal influenza. This has led to the 2009 influenza pandemic sometimes been characterised as a mild pandemic, or even as a ‘false pandemic’.

When comparing the deaths from seasonal influenza with the reported deaths from the pandemic influenza, the following has to be taken into account: For seasonal influenza exact number of deaths are not accurately measured in any EU country. Instead, statistical methods are used to estimate mortality through looking at the surges of deaths (excess mortality) that take place in association with influenza epidemics. 

There have been around 3,000 confirmed deaths from the pandemic influenza. This is based on confirmed cases of influenza (usually through laboratory tests). This is a very different way of measuring mortality from the estimate method.

It is thus grossly misleading to compare the estimates from non-pandemic years with the numbers of confirmed deaths from the pandemic.

Accurate assessments of pandemic deaths will likely be possible only one to two years from now, and then only in certain countries with sophisticated surveillance systems.

It is also misleading to say that the 2009 influenza pandemic is “just like seasonal influenza”, even if the numbers of deaths end up being similar. The pattern of deaths from the 2009 pandemic influenza has differed significantly from the previous seasonal influenza in several ways: 

  1. In the cases reported to ECDC with severe respiratory infection from pandemic influenza who died, nearly 80% are in people under 65 years, while for previous seasonal flu the proportion is about 90% in people over 65. 
  2. 30% of the pandemic deaths are in entirely healthy people.
  3. Surveillance of all-cause mortality in a number of EU countries has shown an increase in deaths among children during the pandemic as found by the EUROMOMO system and published in Eurosurveillance. (See Eurosurveillance., Volume 15, issue 5, 4 February).
  4. A number of deaths have been from Acute Respiratory Distress Syndrome – this is very rare in seasonal influenza.
  5. But it remains true that the majority of deaths have been in people with chronic underlying conditions, following the pattern of the old seasonal influenza.

Importantly not all people who die as a result of influenza have the infection recognized and in some cases the tests are done too late to detect the infection. In other instances there are no tests available. As a consequence it is important to note that the deaths reported as being due to influenza are always an underestimate, this is especially true in the case with seasonal influenza affecting older people but is probably less the case for this pandemic.

What was the number of fatal cases as of April 2010?

Announced number of new and cumulative confirmed fatal 2009 pandemic influenza A(H1N1) cases in EU and EFTA countries, as of Week 17 - 2010

CountryNumber of new fatal Cases since previous weekCumulative number 
of fatal cases
EU and EFTA countries
Austria 40
Belgium 19
Bulgaria 40
Cyprus 8
Czech Republic 102
Denmark 33
Estonia 21
Finland 44
France 344
Germany 254
Greece 141
Hungary 134
Iceland 2
Italy 244
Latvia 34
Lithuania 23
Luxembourg 3
Malta 5
Netherlands 62
Norway 29
Portugal 122
Romania 122
Slovakia 56
Slovenia 19
Spain 271
Switzerland 18
United Kingdom 474

 * Deaths reported from France include 1 in Guyana, 9 in New Caledonia, 7 in the French Polynesia, 7 in La Réunion, 1 in Martinique, 2 in Mayotte, 5 in Guadeloupe and 312 in mainland France.

What is being done in the European Union about the situation?

In the European Union, ECDC is following the epidemiological situation and assessing the risks: daily situation updates including regular risk assessments are published on the Centre’s website, and different types of guidance documents have been prepared, such as information on personal protective measures to be taken, information for travellers, guidance for management of cases and contacts and others. A common European case definition has been developed, which is used for the daily reporting of cases on the EU level. In addition, the diagnostic capacity for this novel virus is being strengthened in the European Member States.

The European Commission is working closely with the EU Member States on all risk management issues within the Early Warning and Response System (EWRS) and EU Health Ministers have got together in extraordinary meetings to discuss the situation and reinforce the need for the EU to work together and join forces.

The development of a pandemic: how does flu spread?

One of the components of the definition of a pandemic virus is that it is a novel influenza virus; therefore many people, if not most people, have little or no immunity to it – less than to ordinary seasonal virus. We do not yet know what proportion of people will be in this situation.

In a pandemic, some people will have no symptoms at all (asymptomatic infections) and many will have mild symptoms. However, a small proportion will have more severe symptoms and will benefit from hospitalisation and a very small proportion of the group will die prematurely, usually from complications of the influenza infection.

The best way of estimating these proportions is to look back to the experience of previous pandemics: those of 1918, 1957 and 1968. These three pandemics differed in many of their characteristics, especially in their severity.

What should I do if I want to travel?

Influenza spreads from person to person through coughing or sneezing, or by direct or indirect contact with respiratory secretions from infectious persons. Therefore, the risk of transmission of influenza can be significantly reduced by some simple methods.

In response to the outbreak of the new influenza A(H1N1) ECDC suggests the following:

1. Before you travel

  • If you have any underlying chronic disease, contact your doctor.
  • Get familiar with simple methods how to protect yourself (see below).

2. During your travel

Simple methods how to protect yourself are:

  • Avoid close contact with sick people: Signs of influenza may be one or more of the following symptoms: fever, cough, sore throat, runny nose, body aches, headache, chills and fatigue. Some people have reported diarrhoea and vomiting associated with infection by the new influenza virus.
  • Wash or clean your hands frequently: Washing or disinfecting your hands thoroughly will help protect you from viruses. Wash your hands thoroughly with soap and water, especially after you cough or sneeze. And don’t just rinse them quickly, you should wash your hands for at least 20 seconds each time. Alcohol-based hand cleaners also effectively reduce the amount of influenza virus on contaminated hands and are easy to use. Liquids or gels are more effective than alcohol-soaked tissues.
  • Avoid touching your eyes, nose or mouth: Viruses are often spread when a person touches something that has been contaminated and subsequently touches their eyes, nose or mouth.

If you are ill and suspect influenza you should:

  • Stay at home or in your hotel room unless you need to seek medical attention. Children with fever or influenza like symptoms should seek prompt medical attention.

The use of prophylaxis with neuraminidase inhibitors (e.g. Tamiflu®, Relenza®) is a decision to be taken by a physician, based on the individual risk assessment.

Persons being immunised with the seasonal vaccine need to be aware this will not protect them against the new influenza A(H1N1) virus.

3. After you return

In case you develop fever (38ºC or more) and influenza-like symptoms (such as a runny nose, sore throat, cough, fatigue, general body pains) within seven days of your return from travel, you should rapidly seek medical attention by telephone, informing the persons you consult about your recent travel, in accordance to your national health authorities’ recommendations.


What should I do to keep from getting the flu?

There are everyday actions that can help prevent the spread of germs that cause respiratory illnesses like influenza. Take these everyday steps to protect your health: wash your hands frequently (and don’t just rinse

them under running water – wash them thoroughly for 20 seconds), try to stay in good general health, get plenty of sleep, be physically active, manage your stress, drink plenty of fluids, and eat nutritious food. Try not to touch surfaces that may be contaminated with the flu virus. Avoid touching your eyes, nose or mouth: germs spread this way. Avoid close contact with people who are sick and avoid crowds and mass gatherings.

What groups are most likely to suffer severe illness if become infected?

A small proportion of those infected have been affected more severely, some have had to go into hospital and a few of these have died despite medical care. However, these are mostly special individuals in ‘risk groups’. This means people who, if they are infected, are more likely to experience severe disease.

Almost all of those who have become very ill or died in Europe and North America have been those in previously recognised risk groups namely:

  • People of all ages with chronic underlying conditions – diabetes, cardiovascular disease, chronic respiratory disease and other conditions which impair breathing, such as extreme obesity;
  • Pregnant women; and
  • Young children (especially those under two years of age).

Overall, pregnant women are more likely to expect more severe illness from influenza A(H1N1)v than other people. The European Medicines Agency (EMEA) has ruled that pregnant women may be treated with the neuraminidase inhibitor oseltamivir.

It should be noted that severe disease and even deaths have, in rare cases, been reported in previously healthy persons. This has even happened in Europe in adults and children (first deaths reported on 10 July 2009). These are to be expected and are a source of concern. These cases are being investigated by the countries.

So far, it is striking in North America and Europe that there is an underrepresentation of older people among those infected and falling sick.

What surfaces are most likely to be sources of contamination?

The virus can be spread when a person touches something that is contaminated and then touches his or her eyes, nose, or mouth. Droplets from a cough or sneeze of an infected person move through the air. The virus can be spread when a person touches respiratory droplets from another person on a surface like a desk, books and door handles, for example, and then touches their own eyes, mouth or nose before washing their hands. Studies have shown that the influenza virus can survive and infect a person for up to 2–8 hours after being deposited on the surface.

What household cleaning should be done to prevent the spread of influenza virus?

It is important to keep all surfaces clean, especially bedside tables, surfaces in bathrooms and kitchen counters, by wiping them down with a household disinfectant according to directions on the product label.

What is the best way to keep from spreading the virus when I am sick?

  • If you are sick, limit your contact with other people as much as possible. Do not go to work or school if ill for seven days or until your symptoms go away (whichever is longer).
  • When you cough or sneeze, cover your nose and mouth with a tissue. Throw the tissue in the bin after you have used it and wash your hands afterwards.
  • Wash your hands often with soap and water, especially after you cough or sneeze. Alcohol-based hand cleaners are also effective.

What is the best technique for washing my hands to avoid getting the flu?

Washing your hands often will help protect you from germs. Wash with soap and water or clean with alcohol-based hand cleaner. We recommend that you wash your hands – with soap and warm water – for at least 20 seconds. When soap and water are not available, alcohol-based disposable hand wipes or gel sanitisers may be used. You can find them in most supermarkets and pharmacies. If using gel, rub your hands until the gel is dry. The gel does not need water to work; the alcohol in it kills the germs on your hands.​

Page last updated 8 Oct 2009