Covid variants fail to defeat vaccine even after six months: study in Cell

Variants fail to defeat the protection of vaccines, which continue to shield us from the virus for a long time because, in addition to antibodies, they stimulate the formation of T cells, immune system cells with an ‘iron memory’ that can ‘unmask’ and fight the virus even when it changes face thanks to mutations

These cells, capable of reactivating the immune response in a very short time, persist in the circulation for a long time, maintaining a reactive response against all variants 6 months after vaccination, averaging around 87-90%, which drops to just 84-85% for Omicron alone, compared to the initial post-vaccination response.

They are the key to long-lasting immune protection, protecting against severe disease for a long time regardless of possible future virus mutations.

These important findings are the result of a study published in the journal Cell by a research team from the La Jolla Institute for Immunology in San Diego, led by Alessandro Sette, of the University of California at San Diego, in collaboration with the group of Professor Gilberto Filaci, director of the Biotherapies Unit at the IRCCS Ospedale Policlinico San Martino in Genoa and full professor of Medical and Laboratory Sciences at the University of Genoa.

“The study makes it possible to predict that vaccine-induced immunity will be very prolonged as well as probably effective against future variants.

The booster dose proves to be the best way to ‘summon’ other memory T cells to the fight, strengthening our line of defence against the virus,” explains Gilberto Filaci.


The immune system’s army is divided into two major ‘legions’ that contribute to an effective immune response.

The first is linked to the activation of B lymphocytes, which are responsible for producing antibodies that are like missiles, capable of recognising and killing cells infected by the virus.

The second is linked to the activation of T lymphocytes, which are immunological memory cells that persist for a very long time even after any drop in antibodies, as happens in subjects vaccinated against COVID, where there is a decrease in antibody levels within six months of vaccination.

“These cells are like perennial sentinels capable of recognising an enemy years and years after the first encounter and of mounting in a very short time an immune response that reactivates the production of specific antibodies: Those that then bind to the virus, preventing or resolving the infection,’ Filaci points out.

‘Thus, the specific ‘memory’ T cells, which are formed after coming into contact with a germ, either through contagion or vaccination, remain in our bloodstream, protecting us from it every time we encounter it: they do this also through the immediate reactivation of the antibody response, thus generating a sort of immunological ‘double shield’, which is essential for long-term protection.


The study analysed the T-cell response and showed that they recognise all ten different variants that have emerged in recent months, including Omicron, and remain capable of providing an effective immune response even six months after vaccination.

Analysing the T-cells of people vaccinated with four different vaccines (Pfizer-BioNTech, Moderna, Johnson & Johnson/Janssen and Novavax), the researchers observed that T-cell reactivity at six months averaged 87-90% compared to the initial post-vaccinal reactivity and fell to just 84-85% against Omicron, regardless of the vaccine received.

The immunity induced by T-cells is therefore long-lasting and significant against all known variants and is not ‘broken’ even by Omicron,” Filaci explains.

When a vaccinated person comes into contact with the virus, even months after vaccination, the T lymphocytes rapidly stimulate the B lymphocytes to produce specific antibodies: in this way, a ‘double shield’ is created against the virus almost immediately and the infection is promptly fought and eradicated much more quickly and effectively than in unvaccinated people.

This is another reason why vaccinated persons, although they can still become infected, generally have mild or even asymptomatic forms of the infection.

Given the results of the tests 6 months after the vaccine, it is very likely that the T-cells of the vaccinated will give rise to long- or very long-lasting immune protection against severe disease, but the booster dose remains very important to further minimise the very slight drop in T-cell response observed 6 months after vaccination.

Finally, it is plausible that the vaccine may also ‘curb’ future variants: the study found that the T cells of each vaccinated individual recognise an average of twenty different pieces of the virus, generating a redundant immune response, i.e. directed against more than one fragment of the spike protein: this makes it less likely that the virus will generate future variants in each of these twenty pieces of molecule, such as to make it totally unrecognisable to T cells’.

Another young Italian researcher, Alba Grifoni, and the American doctor Alison Tarke, enrolled in the PhD programme in Clinical and Experimental Immunology at the University of Genoa, played an important role in the study.

Rector Federico Delfino added: “This study is also an example of how virtuous and productive collaborations and synergies between local and international bodies can be in scientific research, and shows how our PhD courses, if managed with an international vision, can lead to the generation of brilliant young researchers, our hope for the future”.

The pandemic emergency has confronted the scientific community with the need to provide rapid and effective responses through collaborative efforts between different bodies at national and international level,” emphasises Professor Antonio Uccelli, Scientific Director of the San Martino General Hospital.

This study is a clear example of this and demonstrates the ability of Genoa’s institutions to work synergistically with some of the best scholars in the field of Covid research”.

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