How the world caught the flu

Swine flu is the first flu pandemic of the 21st century, but what do we really know about it? And what is likely to happen next in the ongoing drama of Pandemic H1N1?

IN MID-MARCH, news broke that a new strain of flu virus similar to one seen in pigs was infecting humans in Mexico. By mid-April, confirmed cases started popping up in the US and, slowly but surely, the virus crept around the world. Then eventually, after much speculation, the World Health Organization (WHO) officially declared a flu pandemic on June 11th. It was the first to be classified as such in 41 years, by which point around 70 countries (including Ireland) had reported new cases of the virus and the infection was spreading within communities.

As the story bubbled along, the new bug brought with it many problems – not only illness, but also media hype over its potentially catastrophic impact and even consternation as to what to call it.

The term “Mexican flu” was unpopular in its country of origin for obvious reasons, and the pork industry was keen to lose the tag of “swine flu”.

As the virus started to spread, the WHO coined the tongue-twisting handle “influenza type A (H1N1)” and now refers to it as “Pandemic (H1N1) 2009”, yet the term “swine flu” has remained in popular use. But, whatever you call it, the new pandemic virus has been detected in over 120 countries, has killed more than 700 people and its spread is “unstoppable”, according to WHO. So, what have we learned?

How does it compare with older outbreaks?

This is not the first flu pandemic, nor is it likely to be the last. Every year, the seasonal flu sweeps around the world, but scientists can predict the nature of “drifting” changes in the virus and design vaccines accordingly.

A pandemic can happen when a “shift” happens in a flu virus, the resulting strain passes easily between humans and it spreads to different regions of the world. Within the last century, we have seen three flu pandemics with major consequences, the most fatal being the “Spanish flu” in 1918/1919 caused by a particularly nasty H1N1 strain, which killed over 40 million people worldwide. It’s still considered the worst-case scenario on the modern pandemic yardstick.

In 1957 an Asian flu pandemic (this time a H2N2 virus) killed around 100,000 people, then in 1968 around 700,000 died in the “Hong Kong flu” pandemic (H3N2).

In 1997 the first human case of avian or “bird flu” (H5N1) cropped up, and human infections started to build around 2004 and 2005. But, while the H5N1 virus could cause severe illness and even death, it didn’t spread easily among humans and the much talked about pandemic never took flight.

However, the bird flu threat did prompt the WHO to instruct countries around the world to officially prepare for a future pandemic, and from that grew Ireland’s national preparedness plan.

What do we know about H1N1?

There are some advantages to hosting a pandemic in the 21st century – not least being the close surveillance of the virus. Since its emergence, the new H1N1 has been tracked and analysed as it spreads around the world, with scientists combing samples of the virus for mutations or changes in its makeup.

“No previous pandemic has been detected so early, watched so closely in real time right at the very beginning,” reassured WHO’s director-general Margaret Chan.

So what are they finding out? There’s little information in the public domain, but no substantial changes have been detected in the genetic makeup of the virus since its leap to fame in Mexico. However, it continues to be watched because one of the big fears is that the virus will develop resistance to anti-viral drugs such as Tamiflu and Relenza, which can help manage the infection. Already there have been a handful of isolated H1N1 cases showing reported drug resistance in Japan, Denmark, Canada and Hong Kong. None of those strains showed signs of spreading, but authorities (including the Health Service Executive here) are recommending that anti-viral drugs be handed out judiciously to help reduce the chance of more widespread drug-resistance becoming a problem.

Who has proved most vulnerable?

One of the hallmarks of a pandemic flu virus is that it affects young people and H1N1 is no exception. Based on statistics from Canada, Chile, Japan, the UK and the US, most cases are cropping up in patients with a median age of between 12 and 17, according to WHO figures. Data also suggest that people with underlying conditions such as asthma, obesity, diabetes, cancer or heart disease could be at greater risk of severe symptoms.

Media reports have recently leapt on the observation that the virus could put pregnant women at risk of severe illness, and earlier this month the National Childbirth Trust in the UK went so far as to suggest that women considering having a child should delay becoming pregnant. Medical authorities roundly denounced that advice, saying it was a disproportionate response.

Meanwhile, medical journal, the Lancet, this week carries an online report from the US Centers for Disease Control that analysed 34 cases of pregnant women infected with H1N1. They argue that, while pregnant women may not be more vulnerable to infection than the general population, they may be more prone to complications once they have the virus and should be leapfrogged to the top of the queue for treatment if they are infected.

How does the virus affect the body?

Most people who fall ill with the pandemic H1N1 virus are in for several days of discomfort and lethargy, but in medical terms the symptoms are described as “mild to moderate”. A small percentage of patients will have more severe symptoms. So far the death rate from pandemic H1N1 infection runs at less than 0.5 per cent, but the exact molecular events that lead to death from the infection are unclear.

Previous and severe pandemic viruses, such as that of 1918, are thought to have triggered an overwhelming and inappropriate immune over-response in patients who died – the so called “cytokine storm” where inflammation runs riot in the body and can damage tissues and organs.

Is a vaccine near?

One of the most hotly anticipated steps in the strategy against pandemic H1N1 is the preventative vaccine, due to be rolled out in autumn. “Manufacturers are expected to have vaccines for use around September,” says the WHO website, www.who.int.

Vaccine trials are already underway in Australia, and the US National Institute of Allergy and Infectious Diseases (NIAID) is due to start early trials of two pandemic vaccines in August – there is reportedly no shortage of willing volunteers.

And when asked by Naturereporter Declan Butler whether the virus could change genetically and undermine the vaccine, the NIAID's Anthony Fauci was upbeat.

“You never can predict that, but things look encouraging to me from a molecular-virological standpoint. If you look at the molecular and genetic make-up of the virus from the very first isolates in early April, compared to what we are seeing now in late July, it’s virtually an identical virus everywhere. So it doesn’t look like it is under pressure to mutate to a significant degree. We hope it stays that way for the autumn and winter season.”

The best case scenario

As the saying goes: if you have seen one flu pandemic, you have seen one flu pandemic. Predicting how pandemic viruses are going to shape up over time is a dark art, but based on models from previous situations, large outbreaks tend to come in waves a few months apart.

The first wave might be relatively mild, but the second and possibly third waves can bring more serious illness and mortality. The best case scenario for the current H1N1 pandemic is that the virus continues to cause only mild symptoms in the majority of humans it infects, that the vaccinations will protect people against illness and that the anti-viral medication continues to help patients who need it.

The worst case scenario

That the pandemic H1N1 virus undergoes substantial change, possibly swapping genetic sequences with other strains of flu virus, and becomes resistant to anti-viral drugs, causes more severe illness and higher rates of mortality and renders useless the preventative vaccine that is currently being made.

The likelihood of all those “worst case” events lining up in a row is small, but experts point out that even in such a dire situation, medicine is very different now compared with 1918, when the world had just been through a major war, science knew little about viruses and there were no antibiotics to help people recover from secondary infections.

In Tuesday’s HealthPlus: Boosting your immunity against swine flu