Covid-19: the vaccine recall against Omicron only 20% effective?

It is the misinterpretation of an Italian study in pre-publication that has attracted the interest of anti-vaccine networks. The aim of this work was to study the gradual decrease in vaccine immunity against several variants of Covid, including Omicron.

To reach their conclusions, the researchers selected twelve studies out of more than 500 pre-selected at the start. They therefore wanted to re-analyze all of the results of this work in order to draw a final conclusion. The vaccines studied in these twelve works are those of the Pfizer, Moderna and Astra-Zeneca laboratories.

An analysis of each of the studies

Based on these twelve studies, the Italian scientists collected data on the efficacy of two doses against confirmed cases of the Delta variant; the efficacy of two doses against symptomatic forms of Covid-19 due to the Delta and Omicron variant and the efficacy of two initial doses plus a booster dose against symptomatic and asymptomatic forms due to Omicron.

Vaccines whose effectiveness decreases over time

The researchers’ conclusions are as follows:

• The Pfizer and Moderna vaccines have an efficacy against the Delta variant, 14 days after the second dose, of 92.4% and 94.7%;
• For the Astra-Zeneca vaccine, the results are more mixed, around 80% for some studies, identical to that of the other two vaccines for others;
• Three months after vaccination, the effectiveness of the Astra-Zeneca vaccine is lower, reaching 74% against 85.6% and 86.5% for the sera from Pfizer and Moderna;
• Nine months after vaccination, the three vaccines show the same effectiveness, at approximately 70.8%.

The most fragile will require regular reminders

For the Omicron variant, the effectiveness of the vaccines decreases more significantly. For the Pfizer vaccine, it drops from 82.4% 14 days after the injection, to 19% after 9 months. It is from this figure, and from the authors’ note at the end of the article which notes “a rapid decline in the effectiveness of the booster against Omicron is observed, with less than 20% effectiveness “.

For Dr Gérald Kierzek, emergency physician and medical director of Doctissimo, “the decrease in vaccine efficacy is known and is particularly valid for the Omicron variant. Moreover, it remains particularly difficult to measure, because there is a cellular immunity that we do not know how to measure. Finally, it is likely that post-infectious immunity is better than vaccine immunity: this does not mean that vaccines are useless, it simply means that they should be reserved for the most fragile people, who will require reminders regularly to boost their immunity”.