On 11 June 2009 the World Health Organisation (WHO) declared that the 2009 influenza A (H1N1) virus, better known as swine flu, had become a pandemic. A new virus was stalking the globe, with huge potential consequences for the world’s population.

Some people have called it a false alarm, but swine flu is not to be sneezed at (Box 1. What is swine flu?). It is new, which means that few people have immunity to it. It is also highly contagious; since it was first detected in April 2009 it has spread to nearly every country on the planet.

Click for an up-to-date map showing countries affected by swine flu.

So far the death rate seems to be comparable to ‘normal’ or seasonal flu; however, it is affecting younger people more and having less impact on older adults. By January 2010 there had been 12,799 officially confirmed deaths associated with swine flu worldwide (although this is only a small proportion of the total number). In Australia, there had been 37,562 confirmed cases of swine flu and 191 deaths. However, although health authorities don’t have the full picture yet, there are fears that the 2009 H1N1 virus will change into something more deadly. Since most people have low immunity to it, a more virulent form of the virus could be disastrous.

This has happened before. In 1918, when the world was just beginning to recover from the ravages of World War 1, an even more deadly enemy struck – the Spanish flu. This disease started quietly, like swine flu, but then mutated. Within two years an estimated 50 million people were dead from it, which was more than three times the number of people killed in the war.

Related site: H1N1 Vax assist Provides information for consumers on the H1N1 vaccine developed in Australia. (CSL Limited, Australia)

But pandemic need not equate to pandemonium or panic. Today’s global travel might help diseases to spread with frightening speed, but our defences are better. Effective antiviral medicines, for example, are widely available today (Box 2: Antiviral drugs for treating the flu). Even more importantly, we have a much greater ability to develop vaccines to fight new viruses and to produce them on a large scale. In Australia, one company – CSL Limited – has already made an effective swine flu vaccine and manufactured millions of doses to be made available to all Australians.

The making of a vaccine

The ‘H’ in H1N1 stands for haemagglutinin and the ‘N’ stands for neuraminidase; both are proteins found on the surface of the influenza (flu) virus. They exist in many different forms and combinations across the different flu strains, and these are represented by numbers. For example, H1N1 is characteristic of a swine-related flu while H5N1 is a form of the avian (bird) flu.

Flu virus names like H1N1 and H5N1 come from the different forms of the haemagglutinin (H) and neuraminidase (N) proteins on their surface. (Image: Centres for Disease Control and Prevention)

Vaccines work by stimulating the body’s immune system to produce antibodies which recognise antigens – molecules like the H and N proteins – on the surface of the microorganism (Box 3: How vaccines work). To do this, weakened or killed microorganisms – such as viruses – are injected into the body to introduce the antigens to the immune system. In the case of influenza most of the vaccines currently used – and all of those used in Australia – use killed viruses.

The most common technique for growing virus for a flu vaccine is more than 50 years old and can be traced to Sir Frank Macfarlane Burnet, one of Australia’s most distinguished scientists and winner of a Nobel Prize in Physiology or Medicine. In the 1930s, Macfarlane Burnet pioneered the use of hens’ eggs to grow and study viruses. These days the allantoic cavity of fertilised hens’ eggs is used to both create an initial ‘seed’ virus and to scale up production of the virus for the final vaccine.

In April 2009, when health authorities became aware that a virulent new strain of the flu virus had surfaced, a pre-planned process was initiated, led by the WHO. Scientists at the WHO Collaborating Centres for Influenza, isolated three representative strains of the new virus from patients in Mexico and California and sent samples to vaccine manufacturers.

At CSL, the first step in preparing the swine flu strains for vaccine manufacture was a process called ‘reassortment’, which normally takes around four weeks to complete. Most wild flu viruses reproduce poorly under laboratory conditions; reassortment is designed to mix the genes of the wild, virulent flu with those of a harmless ‘donor’ strain (in the case of the swine flu vaccine, an H3N2 vaccine strain). The aim is to produce a hybrid ‘seed’ virus that has the outer antigens of the swine flu virus – so that it will stimulate the production of antibodies in the person being vaccinated – and the inner characteristics and therefore multiplying ability of the high-yielding donor virus.

To produce a swine flu vaccine as quickly as possible, hens’ eggs were injected with the donor virus and one of the three swine flu strains and incubated for about two days. Flu viruses have eight strands of RNA; during incubation, the RNA from the two strains mix together with the potential to produce up to 256 combinations, called ‘reassortants’.

The next step was to select the best vaccine candidate from the reassortants. Those with the outer characteristics of the donor virus – and therefore of no use for the vaccine – were eliminated by adding antibodies that are effective against the H3N2 virus. From the remaining reassortants, the combinations that grew best were selected. These were tested to ensure that they had the outer characteristics of H1N1, and they were also injected into ferrets to test the immune response. The most successful reassortants from this process constituted the seed viruses for vaccine production.

At the CSL laboratory, a series of tests was then conducted to find the optimal growth conditions for the seed virus. These were used to produce the vaccine as follows:

• Seed virus was injected into the allantoic cavities of hens’ eggs, and incubated for about two days to allow the virus to replicate. One egg produces enough virus for around one shot of the vaccine, so to make enough vaccine for every Australian requires many millions of eggs.

• The viruses were extracted from the allantoic fluid of the eggs.

• The purified and concentrated viruses were killed using chemicals and treated with detergents to break the viruses into ‘subunit’ forms.

• The vaccine concentrate containing viral antigens was tested in clinical trials – using volunteers – to determine the amount needed to stimulate adequate immunity, and to ensure its safety.

• Individual doses were packaged into vials and syringes, which were sealed, inspected and labelled to show the vaccine batch, lot numbers, and expiry date.

This process of vaccine development and production although effective, has been described by some as old-fashioned and slow in the face of a highly virulent and contagious disease outbreak. Research is under way to develop faster, easier techniques. There is also hope that, eventually, a ‘universal’ flu vaccine will be developed (Box 4. New flu vaccines).

In Australia, the first flush of swine flu has passed, but further waves are expected. By the time it comes again it is hoped that most of the population will have been vaccinated, so will have developed immunity against the virus. Australians will hopefully be forearmed against, what could still turn out to be, a pig of a problem.

Related Nova topics:

Immunisation – protecting our children from disease

Bird flu – the pandemic clock is ticking

Kissing the Epstein-Barr virus goodbye?

Cancer immunotherapy – redefining vaccines

Box 1 | What is swine flu?

In its current form, the novel H1N1 flu virus produces symptoms similar to those of normal seasonal flu – cough, runny nose, headache, muscle and joint pain, fever, and sore throat. In some cases, it can also cause vomiting and diarrhoea. Like seasonal flu, people catch swine flu by breathing in droplets coughed or sneezed out by an infected person. They can also catch it by touching droplets or respiratory secretions that have landed on a surface, such as a door knob or hand rail, then inadvertently transferring the virus to their mouth or eyes.

Influenza viruses are continually adapting to their environment by mutating and swapping genes – referred to as reassortment. The swine flu is a reassortant virus, and has been created by the natural mixing of genetic material from avian, human and pig viruses over time to produce the current swine flu virus. It is possible that the virus will reassort again or mutate, to emerge later in a more lethal form.

There is debate about the extent of immunity to swine flu that exists within the global human population. Vaccine manufacturers have been surprised that most people require only one shot of vaccine to develop good immunity; usually, two vaccinations are required to produce adequate immunity against a novel flu virus. Older people are surprisingly resistant to the virus, which suggests that they might have acquired immunity by being exposed to related strains in the past.

Related sites

• What is pandemic (H1N1) 2009? (World Health Organisation)

• 2009 H1N1 flu (‘swine flu’) and you (Centres for Disease Control and Prevention, USA)

Box 2 | Antiviral drugs for treating the flu

A vaccine works by stimulating the body’s immune system and preparing it for a possible invasion by pathogens such as a flu virus. If the body is infected by the virus before the vaccine has been administered, however, vaccines are unhelpful. Until recently, the body was then on its own: either the immune system would kick in to eliminate the virus, or it wouldn’t. Now, however, modern medicine has provided an option for treating existing viral infections: antiviral drugs.

Two types of antiviral drug are available for use against the flu today: ion channel inhibitors, and neuraminidase inhibitors. Ion channel inhibitors, like amantadine, block the release of viral RNA (its genetic material) into the cytoplasm of a host cell, affecting the virus’s ability to replicate. Flu viruses, however, rapidly become resistant to ion channel inhibitors, reducing their usefulness in treating new strains.

Neuraminidase is an antigen attached to the surface of the flu virus involved in the release of the virus from its host cells (and therefore the spread of the virus in the body). In the 1970s an Australian scientist, Graeme Laver, isolated neuraminidase. He went on to collaborate with another Australian, Peter Colman, to work out its molecular structure. Ultimately, this resulted in the development of drugs to treat flu.

Related sites

• Antiviral medication and treatment (Influenza Specialist Group, Australia)

• 2009 H1N1 and seasonal flu: What you should know about flu antiviral drugs (Centres for Disease Control, USA)

• Relenza flu treatment (Powerhouse Museum, Australia)

Box 3 | How vaccines work

Our bodies have an immune system that consists of many elements.  We have an innate immunity that helps protect against any invading microorganism, however, once a virus or bacterium gets past our first line of defence the body starts to produce a specific immune response against that organism referred to as acquired immunity.  These specific responses then will usually provide a strong long-term protection against further attacks of the disease.  Vaccines make use of this specific immune response to diseases by introducing a harmless version of a disease-causing microorganism to the body, either killed organisms or organisms that have been modified so that they no longer produce disease (in the case of the current influenza vaccines used in Australia the killed viruses are broken into small fragments to make them even more acceptable to the body). This ‘tricks’ the immune system into developing specific immunity against that microorganism.

The two potent weapons of acquired immunity are the antibody and the T-cell. They operate at different levels: antibodies at the molecular level and T-cells at the cellular level.

Antibodies

Antibodies are protein molecules that move freely in the bloodstream. They are manufactured by white blood cells in response to the presence of molecules on the surface of the disease-causing microorganism. These molecules are known as antigens. A particular antibody will combine best with the antigen that caused the production of that antibody: thus, the antibody is said to be specific for its antigen. Antibodies react chemically with these antigens in such a way that the microorganism or toxin is neutralised and destroyed before a cell is infected.

T-cells

At the cellular level, the body manufactures what are known as cytotoxic T lymphocytes – also called killer T-cells. These white blood cells recognise certain antigens produced by microorganisms and kill cells that harbour them.

If an invading virus evades the antibodies and infects a cell, the T-cells may recognise the infected cell and kill it. Thus the two weapons of acquired immunity, the antibody and the T-cell, complement each other.

Thanks for the memory

Once an infection has been overcome, or a person has been vaccinated, antibodies and T-cells remain in the body, often for years and sometimes for life, acting as a kind of ‘memory’. If the microorganism attacks again, these antibodies ‘remember’ it. They combine with the antigens on the surface of the microorganism and immobilise it so it is no longer able to damage cells in the body. If, despite the efforts of the antibodies, some cells in the body become infected, the memory T-cells are mobilised rapidly to kill the infected cells. Thus, the body has acquired immunity against that particular disease.

Active immunisation

Vaccination works by introducing harmless versions of a disease-causing microorganism or certain antigens of it to the immune system of uninfected individuals. The immune system then produces antibodies and, when required, T-cells specific to the microorganism. The body is thus equipped with the right armoury should infection by the real microorganism occur. The vaccines used in vaccination are of several types:

• live, attenuated microorganisms;

• killed microorganisms; and

• only one, or a few, antigens of the microorganisms. This type is called a subunit vaccine.

Passive immunisation

Protection against some infections may be achieved by passive immunisation. With this type of immunisation, antibodies produced in one person are introduced into another. These antibodies are injected into the host shortly before the expected exposure to a disease-causing microorganism. The antibodies are obtained from the blood plasma of people who have had the disease (or have been immunised against it). Injection of the antibodies confers immediate protection against infection for a short time (weeks). It may also be effective if given shortly after such exposure; for example, after being bitten by a snake or rabid dog.

Related sites

• How your immune system works (How Stuff Works, USA)

• Immunisation – protecting our children from disease (Nova: Science in the news, Australian Academy of Science)

• Vaccines – How and why? (Access Excellence, USA)

Box 4 | New flu vaccines

The ‘egg’ method of vaccine production has worked for more than 50 years. But with a global population of well over six billion people, and growing, the task of producing enough vaccine to protect everyone against the constantly evolving flu virus is daunting – and also a significant cost for health authorities. Moreover, when a deadly form of the virus arises, a turn-around of several months to produce a new vaccine could cost millions of lives. The challenge, therefore, is to develop techniques to produce effective vaccines more rapidly and at a lower cost. Also, because influenza viruses are constantly changing by mutation, and new strains from birds and animals can establish themselves in the human population, scientists are also searching for the ‘holy grail’ of flu research: a single ‘universal’ vaccine capable of warding off all strains of the virus. Several approaches towards these objectives are being tested.

Live attenuated vaccine

Traditionally, the flu vaccine has contained a killed version of the virus (or parts of it). The advantage of killing the virus is that there is no risk that the vaccine will cause the disease when administered; the disadvantage is that the killed-virus vaccine can result in a weak response from the body’s immune system.

Recently, a nasally delivered, live attenuated (weakened) flu vaccine has been produced and is now in use in the United States. Live attenuated vaccines have a significant advantage over killed vaccines because – although they are weakened – they induce an immune response as if they were genuinely infectious pathogens. The live vaccine is able to reproduce to a limited extent in the body, increasing the efficiency of delivery and, often, helping to maintain immunity over time. Live attenuated vaccines stimulate the production of antibodies in a similar way to killed vaccines. But, unlike killed vaccines, they may also stimulate cell-mediated immunity and immunity at the site of infection, in the case of influenza in the respiratory tract. A potential risk with the use of live virus vaccines is the possibility that they might revert to a dangerous form, however, in most cases this is very remote. While they have been very successful for many diseases, technical problems such as stability have delayed their introduction for influenza.

Cell culture

Vaccine virus can be grown in cell cultures, eliminating the need for hens’ eggs. The advantages of cell culture include a reduction in manufacturing time, the elimination of potential allergic reactions to egg components, and the ability to rapidly ‘scale up’ production in the face of a pandemic. The use of a ‘closed’ system is also less prone to bacterial contamination than eggs and protects the operators from the viruses. Cell culture techniques can also be used in combination with genetically-engineered virus antigens to speed up the development of new vaccines.  This was demonstrated recently at the University of Queensland, using a US patented procedure, to develop a swine flu vaccine in just a few weeks.

Reverse genetics

Reverse genetics involves the use of extracted flu virus genetic material to quickly create reassortant vaccine strains without handling dangerous viruses. In some cases this has already replaced the process of culturing new viruses together with a donor strain, and the sometimes laborious process of selecting a vaccine reassortant with the correct characteristics.

Adjuvants

On their own, existing non-living vaccines stimulate primarily the production of antibodies. To increase their effectiveness, an adjuvant can be added to trigger an innate immune response. This aids in the generation of more robust immunity including cell-mediated responses. Adjuvants include aluminium salts, oil-in-water emulsions and some materials with detergent activity; the search is on for others that are even more effective.

Universal vaccine

Existing flu vaccines target the antigens haemagglutinin and neuraminidase on the surface of the virus. These antigenic proteins are constantly changing, meaning that the scientists must continually adapt the vaccines to ensure they remain effective. Some flu proteins, on the other hand, are called ‘conserved’ proteins because they are common to all strains of the virus, and they rarely change. A vaccine that could effectively target a conserved protein might theoretically provide protection against all types of flu, including the swine and avian varieties. Many scientists searching for a universal flu vaccine are focusing on M2, a conserved protein that protrudes from the surface of flu viruses. Others hope to overcome the problems of the constantly changing surface antigens, by targeting a region within the haemagglutinin molecule that is conserved.

Several groups, including Australia’s John Curtin School of Medical Research, have developed candidate universal vaccines and some are being tested in human safety trials.

Related sites

• Australian Broadcasting Corporation
• Universal flu vaccine (Catalyst, 2 July 2009,)
• New swine flu vaccine developed (News in Science, 29 June 2009)

• Scientific American
• Egg beaters (23 February 2004)
• Boosting vaccine power (October 2009, pages 52-59)
• Vaccine manufacturing: Challenges and solutions (Nature Biotechnology, 8 November 2006)
• A long search for a universal flu vaccine (New York Times, 18 May 2009)

Activities

Other activities

• Australian Broadcasting Corporation
• Swine flu – students learn about the influenza virus and swine flu through analysis of a news story. Focus questions and a range of activities are provided to increase the students’ understanding of flu eg, creating a glossary of terms, internet research on the Spanish flu pandemic and creating an educational game/quiz on swine flu.

• Discovery Education (USA)
• Common vaccinations – students review the basics of how vaccines work then create and present a group poster on a common vaccine. Internet access or research materials are required.

• Public Broadcasting Service (USA)
  • Making vaccines – an online, interactive resource in which students can make six types of vaccine in a virtual laboratory.
  • Disease warriors – students play two games that model how vaccines protect a population. They then complete a worksheet to highlight key concepts.

• Science upd8, UK
• PiggiFlu is coming – a complex activity in which students simulate a swine flu pandemic in the school. A simpler classroom-based version is also provided.
• Killer flu – students learn how a virus spreads and make predictions about death rates with and without mass vaccination.

Further reading

21 April 2010, pages 1112-1113
Portrait of a year-old pandemic (by Declan Butler)
Looks at the lessons learnt from the first year of H1N1.

Useful sites

Health Emergency (Australian Government Department of Health and Aging)

• Get vaccinated
  Provides information on the influenza A (H1N1) vaccine available in Australia.
  http://www.healthemergency.gov.au/internet/healthemergency/publishing.nsf/Content/vaccine

• Q & As on pandemic vaccine
  Answers a series of commonly asked questions on the swine flu vaccine, grouped into the following categories: ‘Getting vaccinated’, ‘Travel & international’,  ‘Targeting/priority groups’,  ‘Specific groups’ and ‘Information of safety’.
  http://www.healthemergency.gov.au/internet/healthemergency/publishing.nsf/Content/pandemic-vaccine-qna-toc

H1N1 vax assist (CSL Limited, Australia)

Provides consumer information on the swine flu vaccine (from the Australian manufacturers of the vaccine).
http://www.h1n1vax.com.au

World Health Organisation

• Pandemic (H1N1) 2009
  Links to a range of up-to-date and reliable information on swine flu including frequently asked questions, prevention and treatment of swine flu and regular updates on the swine flu pandemic.
  http://www.who.int/csr/disease/swineflu/en/index.html

• Pandemic influenza vaccine manufacturing process and timeline
  Briefly explains each of the steps involved in making the influenza A (H1N1) vaccine and the time taken for each step.
  http://www.who.int/csr/disease/swineflu/notes/h1n1_vaccine_20090806/en/index.html

2009 H1N1 Flu (Centres for Disease Control and Prevention, USA)

Links to a range of information on swine flu from an American perspective, including 2009 H1N1 flu ('swine flu') and you which covers the symptoms, prevention and treatment of swine flu.
http://www.cdc.gov/h1n1flu/

The H1N1 virus (Scitable, Nature Education)

Presents information and links to reliable, clearly written resources on influenza A (H1N1).
http://www.nature.com/scitable/spotlight/The-H1N1-Virus-6902675
 

Influenza Specialist Group (Australia)

Provides current information on influenza, its treatment and prevention from medical and scientific specialists from Australia and New Zealand.
http://www.influenzaspecialistgroup.org.au

Company vaccine production (The European Scientific Working Group on Influenza)

Provides a video showing the egg-based procedure for producing flu vaccine. (8.54MB)
http://www.flucentre.org/?q=node/156

Australian Broadcasting Corporation

• Experts debate swine flu mutation (In Depth, 4 August 2009)
  Discusses an outbreak of swine flu at an Australian piggery.
  http://www.abc.net.au/science/articles/2009/08/04/2645434.htm

• Influenza (ABC Health and Wellbeing, 8 July 2004)
  Explains what influenza is in terms of the types of flu viruses, symptoms of flu and prevention and treatment options.
  http://www.abc.net.au/health/library/stories/2004/07/08/1831345.htm

The 'flu' (Department of Molecular and Cellular Biology, Harvard University, USA)
Provides a useful summary of features of the flu, the infection process, viruses that have caused pandemics and prevention strategies.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/I/Influenza.html

A/H1N1 fatal during pregnancy (Science Alert, Australia)

Highlights findings of a study on the dangers of swine flu during pregnancy.
www.sciencealert.com.au/news/20102203-20744.html

Glossary

adjuvant. A substance that increases the effectiveness of a vaccine. Adjuvants used in combination with vaccine antigens enhance the body’s immune response. Examples include aluminium salts, oil-water emulsions and some detergent materials.

allantoic cavity. The cavity of the allantois within an egg, a membranous sac which is involved in gas exchange, storage of wastes and absorption of nutrients for the developing chick embryo. For a diagram see The anatomy of a ten-day old embryonated egg (Food and Agriculture Organisation of the United Nations).

antibody. A protein produced by the body’s immune system in response to a foreign substance (antigen). An antibody reacts specifically with the antigen that induced its formation to help the immune system inactivate a toxin or microorganism. Our bodies fight off an infection by producing antibodies.

antigen. Any foreign substance, usually a protein, that stimulates the body's immune system to produce antibodies. (The name antigen reflects its role in stimulating an immune response – antibody generating.)

attenuated. Weakened, less virulent. An attenuated virus is a live but weakened version of the virus. They are used to make vaccines that stimulate a strong immune response without causing disease.

cell culture. The artificial culture of cells under laboratory conditions. The cells are placed in a medium (often liquid) with the appropriate conditions, nutrients and chemicals to allow growth. Canine or monkey kidney derived cells can be cultured and used to grow influenza virus to produce a vaccine. Cell culture has the potential to rapidly develop and scale up production of vaccine virus in place of egg-based culture of the virus.

innate. Natural, inborn. The innate immune system is immunity that is naturally present and non-specific ie, it is not stimulated by exposure to an antigen. The innate immune system prevents infection by microorganisms in general eg, through the skin barrier, mucus secretion, stomach acid and non-specific white blood cells. It also aids in the production of a specific immune response.

mutated. Describes genetic material that has changed in amount or arrangement. A change in the sequence of a gene can be harmful or beneficial to an organism, and is a source of genetic variation. A mutation may enable a microorganism to evade detection by the immune system and cause disease, even though a person has been previously infected.

pandemic. The worldwide outbreak of a disease.

pathogen. An organism capable of causing a disease.

RNA (ribonucleic acid). A nucleic acid similar to DNA. In most organisms, RNA serves as a ‘read-out’ of the genetic information in DNA to facilitate various aspects of cell metabolism, particularly as a message for protein synthesis. However, in some viruses, including influenza, RNA is the primary genetic material instead of DNA, and is more prone to mutation than DNA. For more information see RNA (Nobelprize.org).

seed virus. The starter culture of virus for producing vaccine virus. An adapted virus from which larger quantities can be grown. Many of the seed viruses used for producing the flu vaccine are hybrids of pathogenic strains and a safe, fast growing strain. The resulting viruses are safer and easier to grow in quantity but still with the correct antigens to induce a protective immune response.

toxins. Substances, produced by microorganisms, which affect the functioning of another organism.

virulent. Able to cause severe illness or death. The virulence of an infective microorganism is measured as the proportion of people infected by the microorganism, who become severely ill or die.