Soon, the statistics will no longer show “delta variant” or “alpha variant”, but “L452R” mutation – fairly typical of delta – or “E484K” for example.
In the meantime, the delta variant sometimes reaches maddening levels. The graph below indicates its percentage of detection over the last four weeks (in yellow), but also over the last 24 hours (in blue):
Thus, in Italy, the delta variant rate is “only” 7.4 over the last four weeks, but rises to a quarter on the last screened tests. In the United Kingdom, it accounts for 84% of cases in the last four weeks, and 98% of the last tests analyzed, roughly as in Russia.
It should be noted that the “screening” of tests varies from less than 2% in France or Italy, to 5% in Portugal or the United States, and rises to 30% of positive tests analyzed in the United Kingdom.
These data make it possible to observe the rapid flight of the delta variant when it is present. In the UK, it came into the majority in less than four weeks, before almost completely replacing the alpha variant in six weeks.
A more contagious variant
The variant is about 60% more transmissible than its alpha “predecessor”, which was already 40-70% more contagious than the previous dominant strain. With these data, it should not take longer to replace the alpha strain, wherever the virus is actively circulating and where this variant is already present.
This has concrete consequences: in France, the “effective R” (virus reproduction rate) is currently around 0.7, which indicates that the epidemic is declining. With a more contagious variant, this rate drops to 1.03, and the epidemic progresses again. On the other hand, thanks to the vaccination of the most vulnerable, this should not affect the hospital system.
Vaccination always effective
Because faced with this new avatar of the virus, vaccines are a little less effective, even with two doses. With a dose, however, this is no longer the case. This has prompted governments, especially French and British, to shorten the time between the two doses.
The advancement of vaccination in many countries has on the other hand made it possible to avoid a massacre: the surge in the number of cases no longer translates into an explosion of deaths. But vaccination coverage remains insufficient to curb the spread of the virus.
It also seems that this variant is less easily detectable: it has thus “escaped” sometimes strict border controls, as in Australia: despite drastic measures in force on this island country, cases have been detected – belatedly – in Melbourne .
The relaxation of health measures can also lead to a certain relaxation in populations tired of the persistence of the pandemic.
More “banal” symptoms
The delta variant, finally, sometimes causes different symptoms, easily assimilated to those … of a cold. But with the same risks of serious forms in the most fragile people.
People may think they just had some sort of seasonal cold and continue to go to parties, and infect other people. We believe this is fueling much of the problem
Tim Spector, epidemiologist at King’s College London