Reasons why Covid variant could kill more people are uncertain

Those who may have been comforted in recent weeks by the evolutionary theory of virus mutation – that the more transmissible they become, the less lethal they are – may now be pondering the news that the variant that originated in Kent not only spreads more easily but may kill more people too.

Sarah Boseley www.theguardian.com

Britain’s chief scientific adviser, Sir Patrick Vallance, at the Downing Street press briefing, said it could be that in people over 60 with Covid, 13 or 14 might die in every 1000, instead of 10 as has been the case. The reasons still seem to be uncertain.

The theory of the tradeoff between infectivity and lethality goes that a virus is programmed for survival. If it is too deadly, it will kill off its hosts. So if it starts to spread more, the lethality reduces, because if it didn’t, there would be nobody left to infect.

Sars-CoV-2 has a way around that conundrum. It infects people before they know they are ill. So anyone carrying the virus could be walking around feeling fine and spreading it. By the time someone has been admitted to hospital and is fighting for their life on a ventilator, transmission to other people has already happened.

“The fact the people die is almost like a side-effect,” said Prof Deenan Pillay, a virologist at University College London.

One possible reason is that the increased transmissibility that we have been seeing in the virus is a result of people having a higher viral load – more of the virus in their respiratory system.

“It would then follow if that is the mechanism, then, with more viral replication going on, you can imagine that could correlate with worse disease,” said Pillay.

Until now, that has not been documented, he says. Vallance said they did not think a higher viral load was responsible. He said it may be that the new variant binds more solidly to the receptor and gets into cells more easily or grows more readily in certain cell types.

There is clearly a lot more work to do before they get real answers and the data may not be sufficient yet for that. Pillay points out that the results come from people tested in the community. These are not people with severe illness in hospital so the sample size of those who die is smaller.

Undoubtedly, this discovery is going to make other countries pull up the drawbridge on people wanting to visit from the UK. And that’s the right thing to happen, says Pillay. Border control has worked well in many places, such as Australia and New Zealand.

In fact, what this really tells us is just that we have got to use all the measures to control the virus that we know about already. There is no new way to deal with it. Increased lethality just means we have to try even harder not to catch it. Pillay points out that the first lockdown was more restrictive and better observed than the current one. There is more mobility, for one thing.

The news will strengthen hopes that we can be delivered from our sorry plight through mass vaccination, yet even that now looks less certain. There are suggestions that the variants originally found in South Africa and Brazil may be less susceptible to the vaccines we are now using.

The Mail reported remarks apparently made by the health secretary, Matt Hancock, at a webinar for travel agents. He said there was “evidence in the public domain” that the South African variant reduces vaccine efficacy by “about 50%”. Although he followed up by saying: “We are not sure of this data so I wouldn’t say this in public.”

The good news is that the vaccine manufacturers have consistently said they can tweak the vaccines to deal with variants – and there are indications that they are working out whether and how to do exactly that right now.