Pandemic influenza

What is it?

  • Influenza, or the flu, is a virus disease that can range from very mild to deadly. Flu outbreaks happen around the world every year. But every once in a while, there is a pandemic, a worldwide epidemic that can cause large numbers of deaths. Pandemics, which occurred three times in the 20th century, are unpredictable, impossible to stop, and potentially catastrophic.
  • There are three types of influenza virus, called A, B and C. Influenza A is the most prevalent and is the type that can cause pandemics. It comes in many ‘subtypes’, which are given names such as H1N1, H3N2, et cetera.

A U.S. Army Camp Hospital in France during the 1918-1919 flu pandemic. Credit: U.S. Army photographer.

What are the symptoms?

  • Influenza A and B can cause fever, cough, a runny nose, sneezing, headaches, muscle and joint pains, and a sore throat. In most patients, symptoms last about a week, although the cough can take longer to resolve. In some groups, influenza can become a very serious disease that can end in death. They include pregnant women, children under 5, the elderly, and people with other diseases, such as HIV/AIDS, asthma, heart and lung diseases and diabetes. Between 250,000 and 500,000 people are estimated to die from flu every year around the world.
  • Influenza C causes a mild disease only, mostly in children.

How does it spread?

  • Flu spreads very easily. When people cough or sneeze, they release thousands of tiny droplets laden with the flu virus that can infect other people.
  • There are outbreaks of two influenza viruses A (H1N1 and H3N2) and of influenza B every year. These ‘annual’ or ‘seasonal’ outbreaks happen in the winter in the northern and southern hemisphere, and year-round in tropical areas.
  • One unique feature of flu viruses is that they constantly change the proteins on their surface, which are used by our immune system to ‘recognise’ a threat it has seen before. As a result, immunity against flu often doesn’t last long. When we get infected with, say, subtype H3N2 today, our immune system will learn to defend itself against that strain, but a couple of years from now, H3N2 may have changed so much that the immune system does not recognise it and we get sick again.

What are influenza pandemics?

  • Flu pandemic are rare events; they’re something completely different from annual flu outbreaks. When a completely new strain of flu arrives, nobody’s immune system has ‘seen’ that virus before, so everyone is vulnerable. That means that many more people get sick than during the annual outbreak. If the virus is a very virulent one, many people can die.
  • The most notorious example was the pandemic flu of 1918-1919, also known as the Spanish flu, which scientists think killed between 20 and 40 million people, or between 3% and 6% of the world population. There have been three more pandemics since then, in 1958, 1968, and 2009. All three were far less severe than the Spanish flu, but the 2009 pandemic was unusual because there were many young people among the approximately 200,000 deaths. Young people aren’t usually considered at high risk.
  • A major worry is that a really serious pandemic could strike in the future, for instance caused by the bird flu virus H5N1, if it learned how to spread between humans. Today, a flu pandemic with a 3% fatality rate globally would kill more than 200 million people in less than two years; it could overwhelm health systems worldwide, paralyse countries, and cause chaos.

How is it treated?

  • There are a few antiviral drugs for influenza; the most widely used one is oseltamivir, also known as Tamiflu. According to WHO, it can reduce complications and deaths if given within 48 hours after symptoms begin. But its effects are modest at best, and several influenza strains have developed resistance against oseltamivir; in other words, it’s not a great drug. Still, many countries have stocked millions of doses of the drug to be prepared for the next pandemic.
  • Drugs have virtually no impact on the spread of influenza, because patients still produce lots of virus and can infect others. During a pandemic, drugs might help keep people alive, but they won’t stop the virus from circling the globe.

Oseltamivir, sold under the brand name Tamiflu, has a modest effect at best. Credit: Moroni/Wikipedia

How can it be prevented?

  • For seasonal influenza outbreaks, vaccine companies develop a new vaccine twice a year, once for the northern and once for the southern hemisphere. These vaccines are designed to match the three specific strains (influenza A H1N1 and H3N2, and influenza B) that are going around that year. (There is no vaccine for influenza C.) Flu vaccines don’t work as well as most other vaccines; in some years, they only reduce the risk of disease by half. And because the virus changes from year to year, you need to get a new shot every year to remain protected.
  • In rich countries, the number of people who get a flu vaccines has steadily grown; the U.S., for instance, now recommends it not only for people at high risk, but for everyone older than 6 months. In the 2015/2016 season, 59% of people under 18 got the vaccine, and 42% of those 18 and older. In developing countries, annual flu vaccinations are not widely used because of the cost.
  • Pandemic flu vaccines are an entirely different story. Such vaccines need to be developed very quickly once a new strain emerges and then produced in massive amounts to protect millions or even billions of people. The world currently does not have the vaccine production capacity to do this. In the 2009 pandemic, it took more than 6 months to develop the vaccine and ramp up production, and most of the vaccine was delivered after the pandemic was past its peak. This drove home the fact that the world really wasn’t ready for a flu pandemic. It still isn’t today.
  • Every one of us can reduce the risk of flu transmission by covering our nose mouth during coughing and sneezing and washing our hands frequently.
  • Scientists hope they can come up with a ‘universal’ influenza vaccine that would do away with the need to produce a different shot every year. The ideal vaccine would also protect against pandemic strains and would be cheap and easy to produce in large quantities.

President Barack Obama gets vaccinated against a new pandemic influenza strain in December 2009.  Credit: White House (Pete Souza)

What’s the outlook?

  • Until better vaccines are produced and rolled out worldwide, seasonal influenza will keep exerting a substantial toll every year, especially in countries where few people are vaccinated.
  • Many countries are trying to prepare for flu pandemics, for instance by improving surveillance, increasing their capacity to diagnose flu, strengthening their health systems, and stockpiling drugs. (WHO provides guidance on these issues.)
  • But many countries remain ill-prepared, and currently, pandemic vaccines are impossible to produce fast enough to cover the demand. That means the world is vulnerable when the next pandemic strikes; we can only hope that it will be the milder variety, and not a major killer like the Spanish flu of 1918.


WHO’s main influenza page.

All about influenza type A, B and C.

The story of the 1918 influenza pandemic.

Preventing the flu, by the U.S. Centers for Disease Control and Prevention.