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.
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.
Reasons why Covid variant could kill more people are uncertain Wire Services/ The Guardian.