By Dorothy H. Crawford
“It’s only a virus.” How often do GPs utter those words over the course of a working day? They mean, of course, that your symptoms are mild, non-specific, and don’t warrant any treatment. If you just go home and rest you’ll recover in a few days. But that does not apply to all viruses, and the flu is one that can vary enormously in severity. It may be relatively mild like the 2009 pandemic strain, but it can also be a killer. Just consider the H5N1 bird flu that emerged in 1997, which kills around 60% of those it infects. Now a new bird flu virus is on the loose — H7N9 — that seems to be almost as deadly as its predecessor.
H7N9 was first reported this February in China. By the beginning of June, it had caused 132 known infections, including 37 deaths. This has galvanised flu experts around the world into action. While the virus hunters are trying to locate the origin of the outbreak and stop the virus from spreading any further, other scientists are racing to make a vaccine against it.
So far there is both good news and bad news to report. One piece of good news is that, to date, H7N9 has not succeeded in spreading effectively from one person to another. At present, each new infection seems to be acquired either directly or indirectly from an infected animal — presumably some kind of domestic poultry. But the bad news is that flu viruses mutate quickly and this one already has many of the mutations it needs to spread easily between humans — a recipe for a pandemic.
Again, on the positive side, H7N9 has not yet spread outside China, and at the time of writing, there seems to be a lull in new cases. However, cases are scattered widely across China with no obvious source. Scientists must find its origin in order to stop it from spreading further, generally by closing local live poultry markets and culling infected flocks. But so far they are baffled. While they have detected infected birds in several markets, they can’t find the virus on any of the farms that supply the birds. Until they pinpoint the source, the question of whether to close markets remains an open one; while on the one hand this would prevent transport of infected birds, on the other it risks the trade going underground.
Scientists trying to make a vaccine also face a dilemma. Flu vaccines take several months to prepare so it’s best to get ahead of the game, but start too early and the virus may mutate to become unrecognisable to immunity generated by the vaccine. Generally the gap between the start of an epidemic and vaccine availability is plugged by using anti-viral drugs. But the Chinese often give anti-virals to poultry and so, unsurprisingly, some cases are already resistant to drugs like Tamiflu. Another piece of bad news comes from early stage vaccine development. Apparently, H7N9 only stimulates a weak immune response. This means that around 13 times more of the vaccine would be needed to protect against this virus than is required with other flu strains. So if there is a pandemic there will be less vaccine to go around. Conventional flu vaccine strains are laboriously grown in hens’ eggs, making the whole process difficult to scale up. However, on the plus side, a synthetic vaccine is being developed which could cut the production time by up to a month.
With all the uncertainty about the origin of H7N9, the speed and randomness of its mutations and the unpredictability of its spread, we are left with many unanswered questions to discuss and debate.
Dorothy H. Crawford is the Robert Irvine Professor of Medical Microbiology and the Assistant Principal for Public Understanding of Medicine at the University of Edinburgh. She is the author of Virus Hunt: The search for the origin of HIV/AIDs, as well as The Invisible Enemy: A Natural History of Viruses , Deadly Companions: How Microbes Shaped our History, and Viruses: A Very Short Introduction.
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This is an interesting and topical article but because there is so much hype and misrepresentation by the pharmaceutical companies some things need to be clarified.
The most blatant hype is in the sentence: ” the gap between the start of an epidemic and vaccine availability is plugged by using anti-viral drugs.”
Er no actually! Anti-virals are a product of marketing genius – the pharmaceutical giants have long been faced with the dilemma that pandemic viruses are bad for business. By definition it is a new and highly contagious virus and it takes at least 6 months to develop a vaccine by which time two ‘waves’ will have passed and the main market is as an ingredient in the next annual ‘flu vaccine. A neat coup was pulled in Europe over Swine Flu where GSK sold Pandemrix (a bird ‘flu vaccine that was already licensed) that they said was effective against the new H1N1 before quietly substituting the actual H1N1 six months later (with no change of name or apparently re-licensing) The USA weren’t having any of it and that stunt is unlikely to work again!
Now ‘anti-virals’ have no guarantee that they will work against a new virus – the perfect product really. Plus they need to be administered within a small window when a person first falls ill which is not going to happen during a deadly pandemic; they will sit in a warehouse probably!
The choice of words used by the Pharmaceutical companies is always careful: they say that the new vH7N9 virus ‘has become resistant to’ their anti-virals. This is disingenuous because to say the least because most cases did not receive the drug in the crucial early window so they must be talking about a very small sample of later cases. Hence, applying Occam’s razor, the more scientific position is that there are, at present, no convincing evidence that they are effective.
It is good to see an article flagging up the difficulties experienced when attempting to make a mock up vaccine for H7N7 in 2008 which they abandoned. But I would point out that mutation is not the main worry here. The WHO have been monitoring H5N1 for 16 years now and it hasn’t mutated to become a human virus. Mutation is a random process so this is not altogether surprising. More of a risk is re-assortment between a virus already infectious between humans and a new virus against which we have no resistance whatsoever. The likely scenario here is Vh7N9 meeting an H1N1 in a pig or child and reassorting (gene-swapping) to generate a new virus with all three characteristics required for a pandemic. H1N1 is still the more dangerous as recent cases in Vietnam have shown – young adults being killed rapidly by a ‘cytokine storm’ reaction. Old folk pegging out over several weeks does not fit our present model – though that may need to be revised of course (Popper).
Fascinating stuff but please do be on your guard against the carefully chosen vocabulary offered by the pharmaceutical companies (it is best to paraphrase what they offer!)
The bottom line is that like Foot & Mouth Disease in the UK in 2001 (the most contagious virus known to human or animal medicine) when it happens it will be very fast. And remembering the four days it took the 2000 Fuel Blockade to bring our resupply by road infrastructure to a halt it might seem sensible for the government to encourage us to do a wee bit of preparedness planning whilst the shops are full?
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