I am beginning to grow concerned about the potentially increased infectivity of the recently discovered SARS-CoV-2 variant in England.
A single residue change in the receptor binding domain has potentially increased R0 for this variant by 56%. If this variant is genuinely 56% more infectious, it spells trouble.
tl;dr - Preliminary data makes the infectivity of this new strain difficult to gauge because of noisy real-world externalities. However, a non-peer reviewed paper published recently might just change my mind. According to this paper, the strain that is spreading wildly in the UK and now through most of the EU could hamper the effects of the vaccine roll out for months, all the while increasing cases and deaths in the interim.
The problem with the studies so far, are that they are determined from retroactive model fitting. The paper I have looked at makes predictions which will require data to be validated from the coming weeks. Meanwhile, the prevalence of this strain is said to be 2 months or so behind the UK so some earlier data can be scrutinised from their experience.
The increase in transmissibility was quoted to be initially as high as 70%, while the paper has it at 56%.
Any figure must be taken with a grain of salt because as we know, there are other mitigating factors that could lead to super spreading events or some other vector of exponential growth. That said, the prediction is pretty clear and how accurate it is will become clearer still in the coming months.
As mentioned previously, the US is around 2 to 3 months behind the UK and therefore there will be some inherent advantages in terms of reaching that (now adjusted) level of herd immunity to curb the epidemic.
- R0 has increased. If it was 2.0 then it is now 3.1; if it was 3.0, it is now 4.7. These are very significant increases. In preliminary data, we can see the strain is now becoming the prevalent one in the UK and is displacing all the other variants. Whatever measures were in place that could lead to an R0 of 1.0, would now lead to ~ 60% increases week on week.
- The vaccine and/or infection rate needed to reach herd immunity is now higher.
- This has implications for some vaccines such as the AstraZeneca vaccine from Oxford. A 75% effective vaccine would no longer be viable in stemming the epidemic, granted for personal protection they remain viable. But this furthermore highlights the importance of the Pfizer / Moderna vaccines.
- For the UK, the new strain changes the trajectory and pace of reaching herd immunity. A decline in case and death counts expected for Feb/March could now be completely reversed and even greatly exceeded. It is likely to get much worse before it gets better.
- In the US, assuming current projections for vaccine roll-out, we are likely to remain just ahead of the impact of this wave but huge uncertainties remain. Slowing the spread whilst increasing the production of vaccines will be vital in tilting the odds in our favour. It is also fervent to consider the one dose rollouts to achieve "good" production to twice as many people, as opposed to "perfect" production for half as many. This will be true even more so for the UK.
- Will the world pull together in this humanitarian crises? It would be a long shot, but diverting a significant share of early vaccines to the UK would go about saving a very significant number of lives, particularly if the predicted trajectories play out.