Currently available COVID-19 vaccines do not prevent us from becoming infected with the coronavirus; in fact, the World Health Organization (WHO) estimates that before March, 60% of Europeans will have been infected with the omicron variant. However, these drugs do help prevent us from developing a serious picture of the disease, and now a new study has found that vaccines from Pfizer-BioNTech, Moderna, J&J/Janssen and Novavax are also effective in combating worrying variants of SARS- CoV-2 such as delta and omicron because they induce the immune system to generate T cells, which are capable of identifying and fighting them.
The research has been carried out by scientists from the La Jolla Institute of Immunology (LJI) who have published their findings in a preprint, so they are pending peer review before they can be published in a scientific journal. The data analyzed come from adults who had the complete vaccination schedule but had not yet received the booster dose.
“The vast majority of T cell responses remain effective against omicron,” said Alessandro Sette, Ph.D., Biological Sciences professor at LJI and co-director of the study. “These cells will not prevent you from getting infected, but in many cases they will likely prevent you from getting seriously ill,” added Dr. Shane Crotty, a professor at LJI. “And this is true in all the types of vaccines that we study, and up to six months after vaccination”, highlighted Dr. Alba Grifoni, an instructor at LJI and another of the co-directors of the work together with Sette and Crotty.
Neutralizing antibodies, B cells and T cells defend us
This study has also shown that individuals who are fully vaccinated have fewer memory B cells and neutralizing antibodies against the omicron variant, which coincides with previous information provided by laboratories around the world that showed a decrease in immunity against that variant. Without enough neutralizing antibodies, omicron is more likely to cause an advanced infection, and with fewer memory B cells the body will be slower to produce more neutralizing antibodies to fight the virus.
T-cell “second line of defense” helps explain why an omicron infection is less likely to cause severe COVID-19 in people who have received all of their vaccinations
“Most neutralizing antibodies, that is, antibodies that work well against SARS-CoV-2, bind to a region called the receptor-binding domain, or RBD,” explained Dr. Camila Coelho, instructor at LJI. and co-first author of the study. “Our study revealed that the 15 mutations present in omicron RBD can considerably reduce the binding capacity of memory B cells, compared to other variants of SARS-CoV-2 such as alpha, beta and delta.”
But in addition to neutralizing antibodies and memory B cells, the immune system has other soldiers to fight pathogens: T cells, which, although they cannot prevent infection if we are exposed to SARS-CoV-2, are capable of detecting the virus. virus and destroy cells that have already been infected, preventing it from spreading through the body and causing serious illness.
The LJI researchers believe that the T-cell “second line of defense” helps explain why an omicron infection is less likely to cause severe COVID-19 in people who have received all of their vaccinations. To determine whether the vaccine-induced T cells they detected in the research were really effective against variants such as delta and omicron, these experts analyzed the response of T cells to different viral “epitopes”.
“Vaccinated people have memory CD4+ T cells, CD8+ T cells, and memory B cells to help fight infection if the virus overcomes initial antibodies, and having multiple lines of defense is likely to be a major strength.”
Viruses are made up of proteins that create a particular shape or architecture, and a viral epitope is a particular landmark on this structure that T cells have been trained to recognize. The current vaccines against COVID-19 are designed to teach the immune system to recognize specific epitopes in the initial “alpha” variant of SARS-CoV-2, and as the virus has mutated, its architecture has varied and the risk of infection has increased. immune cells cannot recognize their targets.
The new study’s findings reveal, however, that although the omicron architecture is different enough to evade some neutralizing antibodies and memory B cells, memory T cells continue to act effectively to identify their targets. Overall, at least 83% of CD4+ (helper) T-cell responses and 85% of CD8+ T-cell responses remained the same, regardless of vaccine or variant.
Crotty says it’s likely that omicron-binding memory B cells also contribute to protection against serious disease. “Vaccinated people have memory CD4+ T cells, CD8+ T cells, and memory B cells to help fight infection if the virus overcomes initial antibodies, and having multiple lines of defense is likely to be a major strength,” she concludes. .
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