What is a Pandemic? Influenza outbreaks may be referred to as epidemics or pandemics. An epidemic is a widespread outbreak of disease that occurs in one community, population or region. Epidemics of seasonal or ‘ordinary’ influenza are common and occur at around the same time each year (generally in the winter months in temperate climates).
A pandemic is an outbreak of disease that occurs on a much larger scale. Unlike an epidemic, a pandemic is not restricted to one area; instead the disease spreads around the world and affects hundreds of thousands of people or more globally. Pandemic influenza occurs when a new influenza virus develops that is so different to previous strains that people have little or no immunity to it.
Influenza viruses occur in a variety of animals (including pigs, birds and horses) ) and humans. All influenza viruses change quickly and often to produce new variations or ‘strains’. Sometimes a virus from an animal or bird undergoes a genetic change that produces a pandemic influenza virus that can infect humans. For this to happen, the virus must adapt so that it can spread rapidly and reliably between humans.
There are two possible ways this could happen:
gradual changes over time, increasing the ability of the virus to infect humans
if an animal or person is infected with both animal/bird and human influenza at the same time, the two viruses could combine resulting in a new type of virus able to spread from human to human. This is sometimes referred to as a virus ‘jumping’ the species barrier.
How pandemic and seasonal influenza vary A new pandemic virus spreads in the same way as normal influenza; through the air by coughs and sneezes or by hand/face contact after touching a surface contaminated with the virus.
In a pandemic the symptoms could be more severe than ‘ordinary’ or seasonal influenza and people of any age could be at risk of serious illness because they have little or no natural immunity to it.
When a pandemic virus emerges potentially everyone is at risk and, until a pandemic starts and the characteristics of the new virus are fully understood, it is not possible to predict with any certainty who will be the most vulnerable. It will not necessarily be the same groups as for seasonal influenza (children and the elderly).
It is also difficult to estimate the exact number of people who could be affected as this will depend on the characteristics of the pandemic virus and how capable it is of causing disease.
The symptoms may be more severe than ‘ordinary’ influenza and people of any age could be at risk of serious illness. Because of the numbers of people who could become ill, there are likely to be many deaths.
Treatment of pandemic influenza is similar to that for seasonal influenza. The most effective way to prevent people becoming infected is through vaccination but, as it takes several months to develop a vaccine against the new virus and produce enough for large scale vaccination, it is likely that there will not be an effective vaccine available at the start of a pandemic. In those people who are affected antiviral medicines such as Tamiflu® (oseltamivir) or Relenza® (zanamivir), given early in treatment can help reduce the severity of the condition. There is more information in the Treatment section.
Governments have been stockpiling the antiviral drugs that are used to treat influenza and will use them in the most effective way to try and prevent the rapid spread of infection.
Pandemics in history Pandemics occur infrequently; the world saw three in the last century – the last in 1968. All three pandemics affected enormous numbers of people, causing many deaths and huge disruption to society and the economy. A pandemic can occur in just one wave or in several waves weeks or months apart, each of which may last 6 to 8 weeks.
The three pandemics of the twentieth century were: “Spanish flu” in 1918, “Asian flu” in 1957, and “Hong Kong flu” in 1968. The World Health Organisation has estimated that 40 to 50 million people worldwide died as a result of the 1918 pandemic. It is very important to remember that this was before the advent of today’s modern antiviral medicines.
The subsequent pandemics were less severe but still resulted in an estimated 2 million deaths in 1957 and 1 million deaths in 1968. Again even these later pandemics were before the development of modern antiviral medicines that are now used to relieve the severity of the symptoms.
Global impact: cost, disruption, healthcare Because of the enormous numbers of people who could become ill, an influenza pandemic is likely to cause widespread disruption and would impact on all aspects of daily life with serious social and economic consequences.
According to WHO, current epidemiological models project that a pandemic could result in 2 to 7.4 million deaths globally and if an influenza pandemic were to occur, we could expect:
rapid virus spread around the world because of the high level of global traffic
vaccines, antiviral agents and antibiotics (to treat secondary infections) to be in shorter supply than usual; it is likely to take several months before any vaccine becomes available
medical facilities to be severely stretched and possibly overwhelmed with influenza and non-influenza patients
widespread illness to result in shortages of personnel to provide essential community services.
(Ref WHO Pandemic preparedness)
The impact on the global economy could be significant and organisations would be affected by staff shortages, supply chain disruption, travel or transport restrictions and potential disruptions to essential services.
It is impossible to predict which groups within the population are likely to be worst affected by a pandemic, but the levels of staff absence will vary depending on factors such as the age groups most affected, the need to care for family members, stress, bereavement, possible closure of educational facilities, and potential travel disruption.
Because of the potential impact on everyday life, with modern ways of travel allowing the virus to traverse the globe in literally 24 hours, the WHO and governments around the world have been monitoring the situation and preparing for some years for the likelihood that one day there will be another pandemic.
WHO Phase of alert Experts at WHO are continually monitoring the situation to assess the likelihood of a pandemic emerging. WHO uses a scale of six phases of alert to describe the current threat and the level of pandemic preparations that are needed. Phase 1 is the lowest risk and Phase 6 the highest. The different phases are defined according to how easily the virus spreads between humans and the characteristics of the virus strain. The scales date back to 2005 and have been introduced following the SARS epidemic in Asia in 2007. The influenza A (H1N1) is now the first outbreak in which this scale is being used and tested.
For each phase there are recommended actions for WHO, international governments, communities and industry. The Director General of WHO takes the decision on when to move from one phase to the next and the alert phase is well publicised.
During Phases 1-3 infections are mainly animal infections with few human cases; during Phase 4 there is sustained human-human transmission; Phases 5 and 6 are characterised by widespread human infection. WHO has also defined two periods of activity following a pandemic: the Post Peak phase when there is a possibility of recurrent events and a Post Pandemic Phase when disease activity has returned to seasonal levels.
Phase 1
No influenza virus circulating in animals is reported to have infected humans
Phase 2
Influenza virus circulating in animals is known to have infected humans and is considered a potential pandemic threat
Phase 3
Sporadic human cases or clusters of human infection caused by a virus with pandemic potential but human-human spread is not sufficient to cause community outbreaks
Phase 4
Human to human spread of a virus with pandemic potential is able to cause community level outbreaks. Pandemic risk is increased but a pandemic is not inevitable
Phase 5
Human to human spread of a virus with pandemic potential has occurred in at least two countries within a WHO region. This is a strong pandemic signal and pandemic preparation time is short.
Phase 6
Community level outbreaks in more than one WHO region. Pandemic underway.
Post Peak Period
Levels of pandemic influenza in most countries with adequate surveillance have dropped below peak levels
Post Pandemic Period
Levels of influenza activity returned to those seen for seasonal influenza in most countries with adequate surveillance
Treatments The availability of modern medicines and vaccines means that the world is now better equipped than it has ever been to cope with the threat posed by an influenza pandemic.
Vaccines
In the same way that a vaccine is developed each year to protect against ‘seasonal’ influenza, developing a vaccine against pandemic influenza could help prevent people becoming infected and would be an effective way to reduce the effects of the virus.
However, development of a vaccine against the specific pandemic virus can only begin when the strain has emerged and is fully characterised. Vaccine production will then take several months before enough is available for large scale vaccination, so it is unlikely that a vaccine will be available for the first wave of a pandemic.
Major manufacturers like Solvay will be working with WHO and health regulatory bodies around the world to produce effective vaccines as fast as possible.
Antiviral medicines
Antiviral medications such as Tamiflu® (oseltamivir) and Relenza® (zanamivir) can reduce the effects of the influenza virus in people who have already been infected and reduce the risk of symptoms developing in people they have been in contact with. These medicines have to be given within 2 days of the development of symptoms if they are to help limit the severity of influenza symptoms and reduce the likelihood of serious complications.
The current pandemic will be the first in history where these medications have been available. Please note: Antiviral medications are only available via a doctor/prescription – you should consider very carefully before purchasing these yourself over the internet, as there is a possibility that there will be some fakes on the market. It can never be ascertained in advance whether antivirals will be effective against an influenza pandemic. An antiviral medicine may be effective at the start, but viral resistance may appear during an outbreak.
Governments and health authorities around the world have been developing stocks of antiviral medications, as part of their plan to prepare for a pandemic.
Other treatments
Other treatment for influenza includes rest, ensuring enough fluid intake and taking medicines to help reduce fever and pain (such as paracetamol (acetaminophen) and ibuprofen).
If a complication such as bacterial pneumonia develops it may require additional treatment e.g. antibiotics. It is important to note that antibiotics will only work in some of the complications of influenza. Antibiotics only work against types of bacteria, not against viruses like influenza.
People who become seriously ill with influenza and its complications may need to be treated in hospital.
What is a pandemic?
