Have you ever wondered why flu is still a thing? By which I mean, doesn’t it seem strange that we’ve got fabulous vaccines for measles, polio, rabies etc…. but for a virus that infects 5-15% of the population every year and causes about 250,000 to 500,000 deaths we only have a pretty shaky vaccine which has to be topped up and changed every season. Ever mused on why that is?
Influenza viruses are constantly changing in a bid to escape our body’s territorial army: the immune system. They do this in two ways:
1 Antigenic drift:
Small mutations in the DNA of influenza virus occur as the virus replicates over time. These small changes add up until the body’s immune system can no longer recognise the virus so well, and it can replicate stress-free. The key point here though, is that it’s a gradual, minor change.
2 Antigenic shift:
This is when two types of virus infect the same cell and exchange DNA to form a new type that the immune system won’t recognise. This typically happens when a human flu virus crosses with an animal flu virus, like bird or pig flu. This is a large and sudden mutation and most people won’t have pre-existing immunity – setting up the scene for a pandemic to occur.
So whilst antigenic drift is responsible for seasonal flu and has a vaccine which is only as accurate as our predictions from the southern hemisphere, antigenic shift is the real danger. The problem is that (unlike drift) antigenic shift doesn’t confer any cross protection (where the body recognises at least some parts of the virus and can mount an immune response) and the entire population is vulnerable.
Back in 1918, an unusually deadly influenza pandemic broke out, killing more than the total casualties of the first world war combined. The virus was of the H1N1 strain, which refers to the type of proteins sitting on the surface of the virus.
It’s recently been estimated that if the 1918 flu pandemic broke out today, it would probably kill more than 62 million people. To put this into perspective, an estimated 55.3 million people in the world die each year. The reason for this, despite the advances in modern medicine, is how influenza has evolved to spread rapidly throughout populations combined with the ease of global travel.
The most recent flu pandemic was the 2009 swine flu, which actually had the same H1N1 subtype as the 1918 flu. The world watched in horror as the newly discovered flu strain spread rapidly from its origin in Mexico across the Southern hemisphere.
The 2009 pandemic was responsible for 150,000+ deaths. This isn’t anywhere near the numbers of the 1918 flu, as luckily it turned out to be quite mild.
Current strategies for what to do in case of a new, even deadlier pandemic include a strong vaccination effort, antiviral drugs and combatting pneumonia (which some people are more vulnerable to after flu) with antibiotics.
Unfortunately, most of these mechanisms of protection aren’t really going to reach some of the poorer developing countries, which might enable the virus to gain global traction. What’s more, from past experience, normal supply of antiviral drugs doesn’t tend to meet pandemic demand and brings with it an inevitable lag of supply and demand.
Other ideas include school closures and travel restrictions to try and limit contact between people and prevent the spread of the virus.
(Header image by Navy Medicine from Washington, DC, USA (09-5036-043 influenza) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)%5D, via Wikimedia Commons)