• To understand why vaccinated people were massively affected by the Omicron wave, Toulouse researchers looked at antibody levels.

  • They compared the presence of antibodies before a Delta infection and before an Omicron infection.

    The researchers realized that the contamination took place with Omicron when the level of antibodies was higher.

  • The study shows that the Omicron variant escapes vaccination more than Delta.

The peak of the fifth seems to have passed, after having reached peaks in daily contamination, affecting both unvaccinated people, already infected with Covid-19 or who are up to date with their booster dose.

And if many vaccinated people had already been affected by the Delta variant, they are even more likely to have been contaminated by Omicron.

To understand this state of affairs, Toulouse researchers looked for an answer in the levels of antibodies present just before infection.

To achieve this, they used the serologies of vaccinated people, mostly one and two doses, who were then contaminated either by Omicron or by Delta.

And they ran their mathematical model.

"Different levels of antibodies at the time of reinfections according to the variants"

“We saw that there were different levels of antibodies at the time of reinfections depending on the variants, explains Chloé Dimeglio, biostatistician at the virology laboratory of the Toulouse University Hospital (Haute-Garonne) and author of a study on the subject. appeared in

The Journal of Infection


90% of Omicron reinfections occur in people whose level of antibodies immediately before is less than or equal to 6.967 BAU/ml of blood, which is very important.

While 90% of Delta reinfections occur in people whose total antibody levels are less than or equal to 2.905 BAU/ml.


It also means that 10% of infections are above these already high antibody levels.

By way of comparison, a previous study had shown that 90% of the infections observed with Alpha occurred at levels less than or equal to 1.098 BAU/ml.

It is therefore necessary to have a very high level of antibodies to pass through the Omicron wave.

“But these are levels which say that one can become infected, that does not say the level of severity, weighs the researcher.

We know that the higher the level of antibodies, the less chance there is of ending up in intensive care.


The fact remains that we are more likely, despite its two or three doses, to see its self-test turn positive with Omicron than with its predecessors.

“We knew that Omicron escaped vaccination more than Delta, continues the researcher.

There, we see at what level of antibodies we can become infected with Omicron, even if we have been vaccinated up to three times.

The antibodies synthesized in the vaccine as it is currently supplied do not completely neutralize the Omicron.


The study supports and complements that of scientists who recently reported that neutralizing antibody titers against Omicron were 17 to 22 times lower than against the Delta variant.

Hence the interest in developing a new vaccine synthesized to adapt to new and future variants, which is in progress.


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  • Video

  • Variant Omicron

  • Variant Delta

  • Toulouse

  • Health

  • Coronavirus

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