The CDC data that led to the decision to give the green light to the third dose for over 65 or immunosuppressed: after 120 days the effectiveness of the BioNTech vaccine against hospitalizations decreases from 91% to 77%. Almost unchanged that of Moderna at 92%. Johnson & Johnson at 71%
On Friday in the USA a scientific advisory committee of the Food and Drug Administration (FDA) has recommended the use of the third dose of Pfizer for people with over 65 or frail starting from six months after the second dose. The committee has not yet decided to extend the third dose to everyone, as is the case, for example, in Israel.
A few hours before the recommendation, the Centers for Disease Control and Prevention (CDC) published some data indicating that the level of protection against hospitalizations offered by the vaccine Pfizer declines over the next four months to complete vaccination: one of the reasons that led to the third dose (here everything we know about the effectiveness of the booster).
The results in preventing hospitalizations
Specifically, from two weeks after the second dose Pfizer four months later, the recipients were protected from hospitalization at 91%; after 120 days, however, the effectiveness of the vaccine against hospitalizations dropped to 77 percent.
The vaccine Modern did not show a comparable decrease in the same time frame: after four months the efficacy against severe disease was evaluated al 92%, a level practically identical to its effectiveness before then (by 93%). (Here the article in which he talked about the efficacy and duration of Pfizer and Moderna vaccines).
A third vaccine, the single-dose, is also authorized in the US Johnson & Johnson, whose effectiveness in preventing hospitalizations has registered 71% overall.
The study included 3,689 adults without immunocompromised conditions, admitted to 21 US hospitals in 18 states from March 11 to August 15, and an additional 100 healthy volunteers enrolled in three hospitals 2-6 weeks after full vaccination.
The Moderna vaccine also produced higher post-vaccination antibody levels than the other two vaccines.
How the differences are explained
Other studies have shown Pfizer’s effectiveness against hospitalization remained above 90%, despite the spread of the Delta variant: the analyzes are not in agreement.
However, the overall protection against hospitalization remains high: but how the differences are explained between vaccines?
Meanwhile, the vaccine Pfizer has often been distributed before or in any case a weaker people, all factors that may have influenced the effectiveness calculations.
Then some assumptions were made to explain the best data of Modern: its protection may last longer because its dose of mRNA – the genetic code that teaches the immune system how to recognize the coronavirus spike protein – three times greater compared to Pfizer’s.
Another important variable could be the time elapsed between the two doses, with four weeks recommended for Moderna and three weeks for Pfizer.
Covid vaccines all appear to have been more effective in countries that have applied longer time frames, such as the United Kingdom and Canada, than in the United States and Israel.
And in Italy?
Vaccination effectiveness also depends on the severe case definitions and a lot from how much the virus circulates in a country: where there are no mitigation measures and few vaccinated, the virus still infects more and a percentage of the infected are also vaccinated people who can (albeit to a lesser extent) end up in hospital.
In Italy data from the latest monitoring by the National Institute of Health (ISS), released Friday, show better numbers: an effectiveness against vaccine hospitalizations by 93.1% and 95.4% against hospitalization in intensive care (period 4 April-12 September).
There are no separate data for each vaccine, but in Italy Pfizer is administered in a large majority: over 58 million doses already administered, compared to about 10 million for Moderna, 12 million for AstraZeneca and just under 1.5 million for Johnson & Johnson .
September 18, 2021 (change September 18, 2021 | 16:56)
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