Faced with the meteoric rise in Covid-19 cases, the French government is emphasizing the vaccine booster campaign. A total of 21,933,063 people received a booster dose, according to figures released Friday, December 24 by the Ministry of Health. That is to say nearly a third of the French population. But how long does this booster dose protect against the new Omicron variant?
A study by the British Health Agency (PDF document), published Thursday, brings the first elements of answer as to the duration of the effectiveness of the vaccine booster. She suggests that the protection conferred by a booster dose to prevent lSymptomatic forms linked to Omicron erode faster than with the Delta variant. Franceinfo summarizes the main information of this report.
After 10 weeks, protection against symptomatic forms drops to 50%
With a vaccination schedule entirely carried out with Pfizer-BioNTech, data from the British agency suggests protection of the order of 70% against symptomatic forms linked to the Omicron variant, just after the injection of a third booster dose. But this protection quickly wanes over the weeks. Thus, the study suggests that it drops below 60% after five to nine weeks. From ten weeks after the booster, it only fluctuates around 45%, according to the study.
Moreover, this decrease appears more marked after two doses of AstraZeneca vaccine, then a booster dose with Pfizer-BioNTech. Protection against the symptomatic forms of Omicron then appears to decrease from 60%, two to four weeks after the booster injection, to about 35% as of ten weeks after it.
The analysis also looks at the duration of effectiveness of a booster dose with Moderna to counter symptomatic forms of the Omicron variant. With two doses of Pfizer-BioNTech, followed by a third injection of Moderna, the data suggests a level of protection that remains around 70-75% nine weeks after the last injection. However, the data concerning this type of vaccination schedule have a large margin of error. They must therefore be viewed with caution.
Finally, by way of comparison, the British study also studied the evolution of the effectiveness of a booster dose against Delta. The data show a better persistence of the level of protection conferred by a booster dose against the symptomatic forms linked to this variant. In a three-dose Pfizer-BioNTech vaccine regimen, protection against Delta appears to remain around 90%, even more than 10 weeks after the last injection.
Results to be interpreted “with caution”
The British health agency, however, warns of the need to interpret “with caution” these first data. On the one hand, the study was carried out among a relatively small sample of people, the authors point out. In total, the analysis is based on some 147,587 Delta variant cases and 68,489 Omicron variant cases.
On the other hand, the study is not based on a representative sample of the entire British population and may include bias, especially in the profile of people infected with Omicron.
Data on serious forms expected within “a few weeks”
For the time being, the number of severe forms of Covid-19 linked to the Omicron variant is “insufficient” to determine the ability of booster shots to prevent hospitalizations. “It will be a few weeks before the efficacy against serious diseases with Omicron can be estimated”, according to the report. The British Agency is however reassuring.
“With the other variants, the efficacy of vaccines against serious diseases was significantly higher than that against moderate forms.”
British Health Agencyin a report published on December 23
In view of these precedents, it considers “likely” that the protection conferred by vaccines against severe forms of the Omicron variant be “significantly higher” only for moderate forms. “This scenario is very likely to happen again. But the question is what level of protection we will be at.”, comment Cyrille Cohen, immunologist and member of the Advisory Board on Clinical Trials of Covid-19 Vaccines to the Parisian (paid item).
Regarding the severity of infections linked to Omicron, two other British studies, published on Wednesday, are hopeful. They suggest that infections with Omicron variant are less likely to cause hospitalizations compared to the Delta variant. These works, which have not yet been submitted for proofreading, do not, however, make it possible to establish whether this difference is due to the characteristics of the Omicron variant or the fact that it comes up against more immune populations.