It is true, the protection from a very infectious variant such as the Delta decays in a few months, but the tens of millions of infections spared in England and the effectiveness of the third dose in Israel dispel all doubts.
A new report from the Public Health England (Phe), just released, contains detailed data about the efficacy of vaccines against the Delta variant of the coronavirus. Although we have discussed it many times, each new source of data must be considered because it strengthens the basis from which to start in any political choice regarding containment measures, obligations to be imposed on citizens, vaccination campaigns and so on. So, let’s see: first of all, considering the trend of cases between vaccinated and unvaccinated up to the first half of June, and putting together the effects of the four vaccines authorized in England, the Phe reports a symptom prevention capacity equal to 79 per percent (in a 95 percent confidence interval between 78 and 80 percent) and an ability to prevent extraordinary hospitalizations, because it is 96 percent (in a range between 91 and 98 percent) .
At the population level, the English PEE estimates that up to 20 August 24,088,000 infections, over 143,000 hospitalizations and 105,900 deaths have been avoided by vaccines in England; given the period considered, these estimates include the effect of vaccines on the Delta variant, e they give an idea of the damage that a vigorous vaccination campaign like the British one could have avoided to the United Kingdom. In this regard, the Phe calculations, based on the observed data, leave little doubt: in a series of graphs published on page 21 of the report, we note the enormous protection offered by vaccines also in terms of infections starting from April and including the peak recorded in July, in the midst of the explosion of the Delta variant epidemic. It is obvious that the protection is not total; and it is likely that in the case of infections it is not as high as before; however, the combined decrease in the probability of infection and the decrease in the probability of transmission for vaccinated subjects is obviously still a decisive factor, given the tens of millions of infections prevented (not to mention the rest).
On the other hand, that the protection of vaccines against Delta infection is not eliminated is also confirmed by a large population study conducted in Norway, just published: in this case it is noted how the “raw” protection rate from infection is equal to approximately 86 percent, while that corrected for a series of risk factors for infection (age, geographic origin, sex and others) is approximately 65 percent; This means that infections among vaccinated by the Delta variant are equal to one third of those occurring among unvaccinated subjects; and since the transmission rate from vaccinated to other subjects is reduced (due to the very short duration of the window of infectivity), it is evident that, globally, at the population level the protection is good, even if not equal to that offered against previous variants. The point, of course, is that both Norway and the United Kingdom have spent a shorter time on average since the second dose than in states such as Israel; in that country, in fact, the protection seems to be lower in proportion to the distance elapsed between exposure to the virus and the completion of the vaccination, thus explaining why the Israelis were on average more exposed when the Delta variant arrived.
The decay of the sterilizing immunity in a few months (but not of the clinical protection) therefore seems to be the decisive factor in explaining what has happened and is happening in the presence of a very infectious variant such as the Delta; and that this may be the determining factor, moreover, is demonstrated by the data released in a preprint by the Israelis, data that show how the restoration of sterilizing immunity through a third dose of Pfizer vaccine is sufficient to recover the effectiveness of the vaccine. very high levels, even against the Delta variant. At this point, all the pieces of the puzzle seem to fall into place: vaccines are effective (all), but protection from infection decays in a few months; this factor, much more important than the immuno-evasiveness of the Delta variant, is evident by studying the effect of vaccination campaigns that took place at different times in different countries, compared to the moment of arrival of the delta variant in those countries; Finally, the tens of millions of infections spared in England, plus hospitalizations and deaths, and the efficacy of the third dose in Israel should, taken together, be a strong enough reminder to stop asking questions about vaccine efficacy. as if no answers had been obtained.