CHAPTER 4 Influenza A (H1N1) The Pandemic 2009
In April 2009 the first cases of a new strain of influenza were identified in Mexico and then new cases in the USA were classified as a new type of influenza virus. Within days, 2 Scottish people who had recently returned from holiday in Mexico were identified as the first UK cases. This new influenza strain was identified as Influenza A (H1N1)v. In response to initial reports of significant illness and death in Mexico, the UK and Scottish Governments and Public Health Organisations prepared to respond to a potential pandemic. The existing contingency and pandemic influenza plans were enacted and UK-wide political, civil service and scientific advisory structures were urgently established to manage the UK's response to the potential pandemic. The (H1N1)v virus spread very rapidly across the world and the World Health Organization ( WHO) officially declared a pandemic on 11 June 2009.
Like seasonal flu, infection with influenza A (H1N1)v could cause little or no symptoms, or cause an unpleasant but self-limiting disease. However, this virus did cause severe illness in a minority of people who experienced bronchitis, viral pneumonia or secondary bacterial pneumonia. Other complications of (H1N1)v included ear infections, tonsillitis, septic shock, meningitis and encephalitis. The groups of people most likely to be admitted to hospital were those with underlying medical conditions and pregnant women. Complications in pregnant women included pneumonia and cardio-respiratory complications.
Ministers took the key decisions within the UK Civil Contingencies arrangements designed to respond to major threats to the UK population. These UK-wide arrangements ensured that decisions were taken as soon as evidence was gathered and reviewed and consensus was sought across the UK countries. Once taken, decisions were rapidly implemented and shared openly and quickly with the public via the media. The relative novelty of this new strain of influenza meant however that time was necessary to collect enough information to estimate the potential impact of (H1N1)v on the UK population.
The Scottish Government responded to the pandemic using previously determined and practised resilience and health protection structures. The overall response was effectively composed of two phases: the containment phase which aimed to limit the spread of influenza infection and the treatment phase which aimed to mitigate the impact of influenza on health and ensure the continued routine functioning of society. The UK operated a containment policy for some two months from the emergence of the (H1N1)v virus. The containment phase included:
- Testing patients suspected of having (H1N1)v
- Offering antivirals to all suspected or confirmed cases
- Taking throat swabs from suspected cases
- Treating cases without waiting for diagnostic confirmation
- Contact tracing and prophylaxis of close contacts with antivirals
- Closure of schools based on health risk assessments
- Self-isolation of cases in the community
- Investigation of cases and contacts.
The purpose of containment was to slow the spread of the virus in the population and gather more information about the virus, including its severity, the groups at most risk and transmissibility of the virus. This information would increase the effectiveness of any future pandemic-specific vaccination programme.
As the pandemic progressed affecting many communities, Scotland moved into the treatment phase. Surveillance, investigation and risk assessment processes were adjusted and continued. Emphasis was switched to limiting impact by treatment and care, infection control and immunisation. Health Protection Scotland ( HPS) worked closely with other UK health protection agencies to ensure a consistent UK response.
As the pandemic evolved, it became clear that the original information coming out of Mexico on the severity of the illness was not being replicated in Europe and that the impact of the (H1N1)v pandemic would not be as severe as first feared. (H1N1)v mainly affected younger people who on the whole, had better health. However certain groups of people were particularly affected by this influenza strain:
- Those with ongoing illnesses such as heart disease, respiratory disease and diabetes
- Pregnant women
- Children under 5 years of age.
Significant numbers were admitted to hospital in Scotland and sadly a proportion, some of whom had been previously healthy, died. In light of this evidence the UK Health Departments, with expert scientific advice, offered immunisation to defined groups in the population with the aim of lowering their risk of significant disease and death. In addition frontline NHS and social care staff were offered the vaccine to reduce their risk when caring for those ill with (H1N1)v and to limit the possible effect on health and social care provision.
The (H1N1)v immunisation programme formed an important part of the overall UK pandemic response aiming to mitigate the impact of (H1N1)v rather than further limiting spread. Health Protection Scotland co-ordinated the influenza A (H1N1)v vaccination programme working with the Scottish Government, 20 NHS Boards, 1,024 General Practices, the Scottish Prison Service, and 32 local authorities. The Scottish Government established a Steering Group to oversee the programme.
Surveillance: This was a key part of the response to (H1N1)v; monitoring the spread and impact of the infection in Scotland. The Scottish Influenza Surveillance Reporting scheme collected information on the number of consultations for influenza like illness or acute respiratory illness from Scottish General Practices. There was an increasing trend in consultations until mid to late November followed by a sharp decline in December and a rise to a further, smaller peak in late December, followed a decreasing trend (see Figure 8).
Figure 8: consultation rates PIPeR practices
Although experts eventually considered that (H1N1)v was a virus causing illness of relatively mild severity, influenza (H1N1)v still caused considerable illness in Scotland. From May 2010 nearly 100,000 people in Scotland were prescribed courses of antiviral treatment. Figure 9 shows the similarity in the time trends of presentations of influenza like illness to GPs in Scotland and of the proportion of throat swabs submitted and found to be positive for (H1N1)v. The circulation of the (H1N1)v Influenza virus reached its height in the final weeks of 2009 and effectively ceased circulating after the first 3 months of 2010.
FIGURE 9: ILIARI and swab positivity for (H1N1)v among GPs in Scotland 2009/2010
Immunisation: On 13 August 2009, the Scottish Government announced details of the clinical priority groups for Phase 1 of the immunisation programme: Ministers agreed that frontline health and social care staff workers would also be offered vaccination alongside the first priority groups as these staff were at increased risk of infection and of transmitting that infection to susceptible patients. In September 2009 the Scottish Government issued further guidance on the priority staff and occupational groups including definitions for staff providing healthcare in non NHS settings that would also be included in the vaccination programme.
In November, 2009, Phase 2 of the immunisation programme offered vaccination to all young children aged over six months and up to five years of age. The reason was that children under the age of five years had consistently the highest levels of hospital admissions with the (H1N1)v infection.
Uptake figures for the (H1N1)v vaccine campaign in Scotland, estimated in April 2010 were:
- Those in clinical 'at risk' groups 54%
- Those aged under 5 years 66%
- Those aged 5-64 years 52%
- Those aged 65 years 56%.
Apart from the thousands of people treated with (H1N1)v influenza at home or by primary care services, a large number of people experienced more severe illness. As at 1 March 2010, a total of 1540 people with confirmed (H1N1)v infection had been admitted to hospital. Sixty-nine people died of confirmed (H1N1)v infection. Of those who died about 70% had underlying medical conditions including diabetes, respiratory conditions, obesity, renal/liver conditions, congenital abnormalities, immuno-suppression, pregnancy and cancer. In some cases, the patient had more than one of these conditions. Figure 10 below shows how numbers admitted to hospital increased sharply during the last 3 months of 2009, dropping equally sharply in the first few weeks of 2010 as the levels of circulating virus fell away and as increasing numbers were protected by vaccination.
Figure 10: cumulitive number of hospitalised cases of influenza (H1N1)v including new cases each week and death 09/10
On 10 August 2010, WHO Director-General Dr Margaret Chan announced that the (H1N1)v influenza pandemic was over. However, localised outbreaks of various magnitudes are likely to continue. The world is now in the post-pandemic period.
It is however, expected to re-appear as the dominant strain during the next flu season in 2010-2011. Based on knowledge about past pandemics, the (H1N1)v (2009) virus is expected to continue to circulate as a seasonal virus for some years to come. While the level of concern is now greatly diminished, vigilance on the part of national health authorities remains important. Such vigilance is especially critical in the immediate post-pandemic period, when the behaviour of the (H1N1)v (2009) virus as a seasonal virus cannot be reliably predicted.
In Scotland, the seasonal trivalent vaccines that are available do cover the (H1N1)v (2009) virus. The (H1N1)v virus is not currently known to be circulating in Scotland. But it is certain it will cause flu like illness in Scotland this winter and those in the groups offered influenza vaccination should have it.
I would like to take this opportunity to pay tribute to the unceasing efforts of all involved in responding to the 2009 pandemic. A great many people in many different services worked extremely hard to provide a coordinated and successful response to what could have potentially been a very severe threat to the health and wellbeing of the people of Scotland. Those services responding did so with a degree of professionalism that allowed normal services to continue to be provided.
Finally, we must not drop our guard. This was the first pandemic for nearly 50 years and its virulence was not as severe as first feared. However there are still many other influenza viruses out there including the avian strain - H5N1. These viruses constantly change and the probability of a new pandemic with a different virus is much the same as it was prior to May 2009.