For me an important factor is that we have three different pints of data that suggest the new strain is more infectious. First, it’s rapidly replacing the existing strain in areas where it is preset. Second, those areas are seeing surges of infections that don’t occur in other areas. Third, it seems like individuals infected with the new strain have 3 or 4 times the viral load of individuals with the previous strain—which would neatly explain higher transmissiblility. I’m going with an 85% chance that this is genuinely more transmissible.
I’m not at all sure our current wave will fade before the new strain starts making an impact so I’m 50% on two waves.
Higher peak viral load does correlate with more severe symptoms but not that strongly. I think it’s unlikely that this strain is less virulent than the previous one because most transmission happens before symptom onset and there isn’t as much selective pressure for that as their would be for a virus with more normal kinematics. Post herd immunity there’ll probably be selective pressure for longer incubation periods and that might lead to less virulence, but that’s further down the road. Because most severe disease happens when viral load has gone down I figure it’s most likely that how well the virus is able to fool the host’s immune system causes both peak viral load and severe disease but I’m very unsure about this. Still, this is only a half order of magnitude in max viral load and that varies by many orders of magnitude between individuals and is still only weakly correlated with disease severity so even if it has an effect I don’t expect it will be large.
Other sources of evidence (albeit weaker): the nature of the mutations (some of which have been studied prior to emergence of the new strain), the related evidence from South Africa.
For me an important factor is that we have three different pints of data that suggest the new strain is more infectious. First, it’s rapidly replacing the existing strain in areas where it is preset. Second, those areas are seeing surges of infections that don’t occur in other areas. Third, it seems like individuals infected with the new strain have 3 or 4 times the viral load of individuals with the previous strain—which would neatly explain higher transmissiblility. I’m going with an 85% chance that this is genuinely more transmissible.
I’m not at all sure our current wave will fade before the new strain starts making an impact so I’m 50% on two waves.
Higher peak viral load does correlate with more severe symptoms but not that strongly. I think it’s unlikely that this strain is less virulent than the previous one because most transmission happens before symptom onset and there isn’t as much selective pressure for that as their would be for a virus with more normal kinematics. Post herd immunity there’ll probably be selective pressure for longer incubation periods and that might lead to less virulence, but that’s further down the road. Because most severe disease happens when viral load has gone down I figure it’s most likely that how well the virus is able to fool the host’s immune system causes both peak viral load and severe disease but I’m very unsure about this. Still, this is only a half order of magnitude in max viral load and that varies by many orders of magnitude between individuals and is still only weakly correlated with disease severity so even if it has an effect I don’t expect it will be large.
Other sources of evidence (albeit weaker): the nature of the mutations (some of which have been studied prior to emergence of the new strain), the related evidence from South Africa.