Omicron: Why some vaccinated get infected and some don't

The Omicron variant spreads so quickly that it sweeps both the vaccinated and the unvaccinated in its wake.

It seems that in some the vaccines against COVID-19 they work strongly even against Omicron, while on others the effect is weaker.

A recent study, carried out by researchers at Harvard and MIT in Boston, USA, highlighted the spectacular diversity of the human immune system, which is also genetically regulated.

The Doctors of the Therapeutic Clinic of the Medical School of the National and Kapodistrian University of Athens, Lina Paschou (Assistant Professor of Endocrinology), Theodora Psaltopoulou (Professor of Therapeutics-Epidemiology-Preventive Medicine) and Thanos Dimopoulos (Professor of Therapeutics-Hematology-Oncology and Rector of EKPA) summarize the results of this study.(https://www.medrxiv.org/content/10.1101/2022.01.04.21268586v1).

The role of lymphocytes

The researchers took blood samples from 76 volunteers to examine a subclass of immune system cells known as T lymphocytes.

The scientists isolated the participants' T lymphocytes and challenged them with different SARS-CoV-2 variants in experimental test tubes. They found that in 4 out of 5 people (80%) the vaccination resulted in T cells that worked just as well against the Omicron mutation as compared to other variants.

But in 1 in 5 people (20%) the T cells were much less effective against the Omicron mutation, even though they worked well against the original variants. However, it was observed that the booster dose adequately increased T cell responses to the Omicron spike.

When our bodies encounter the SARS-CoV-2 spike protein, either after infection or after a vaccine, some cells, known as antigen-presenting cells, display parts of the viral protein on the outside of T lymphocytes.

This process relies on proteins called HLA. Each of us has different genes that code for the HLA complex. It is therefore possible that genetic differences contribute to the differences in immune response as well. Also, while antibodies decline over time, T cells provide a second line of defense, cellular defense specifically, that lasts longer. They are the cells mainly responsible for the so-called immune memory. Many experts consider them to be our most critical defense against the Omicron variant.

20% show lower vaccine protection against Omicron

In conclusion, 20% of people show lower vaccine protection against Omicron, due to a less effective T cell response. But they are still in better shape than unvaccinated people, especially those who received a booster dose. The optimistic reading of the new study is that 80% of vaccinated people still have a very good immune response against the Omicron variant.

Source: in.gr