Vaccination with adapted vaccines and a combination of different types of vaccines have been shown to strengthen protection against new SARS-CoV-2 variants in adults. However, until now, the data available in adolescents were limited. Now, a new clinical study led by researchers from the European RBDCOV project has shown that HIPRA's COVID-19 vaccine, BIMERVAX®, administered as a booster dose after two previous doses with Comirnaty® (Pfizer/BNTech), induces a broad immune response against multiple SARS-CoV-2 variants in adolescents. The results, published in the journal Pediatrics, come from the phase II clinical trial carried out with 240 adolescents between 12 and 17 years of age in Spain.

"These results provide new data on immunity in adolescents and show that HIPRA's COVID-19 vaccine generates a broad and sustained immune response against different variants of SARS-CoV-2, which is maintained for at least one year. In a virus that is constantly evolving, it is crucial to verify that the immune response induced by the vaccine can neutralise different variants", explains study co-leader Julia García Prado, group leader at IrsiCaixa and scientific director of the Germans Trias i Pujol Research Institute (IGTP).

An answer that goes beyond a single variant

One of the objectives of the study was to assess the ability of HIPRA's COVID-19 vaccine to strengthen immunity against different variants of SARS-CoV-2. To do this, the research team analysed the neutralising antibodies generated against Omicron, as well as against other more ancestral variants of the virus, and compared the results with those previously obtained in adults who had received the same booster dose. The adolescents developed an immune response comparable to that observed in adults –and even higher in some parameters–, reaching the criteria established to consider the response to the vaccine adequate in this population. In addition, the neutralising response extended to more recent Omicron variants, such as XBB.1.5 and XBB.1.16.

Antibodies and T cells: two lines of defense

Protection against infection does not depend solely on antibodies. The cellular response also plays a key role, contributing to infection control and the establishment of longer-lasting immunity. In this study, all adolescents tested showed a detectable cellular response.

To assess this response, the team used different techniques. In addition to conventional T-cell analyses, the team studied the expression of the CXCL10 gene as an indirect marker of T-cell-mediated immunity. This is a promising tool for monitoring the cellular response that requires small amounts of blood, which may facilitate its application in clinical studies with the pediatric population.

"Antibodies are the first barrier against infection, but T cells provide additional and longer-lasting protection. Analysing both responses allows us to have a much more complete view of how the vaccine works", says García Prado.

A long-lasting antibody response and a favorable safety profile

The scientific team followed the participants for a year to study how long the immune response was maintained. Although, as with all vaccines, antibody levels progressively decreased, they remained above the values prior to the booster dose throughout the study period. In addition, the study showed a favorable long-term safety and tolerability profile.

"In the adolescent population, it is especially important to have specific data on both the immune response and the safety and tolerability of vaccines. These results provide relevant information for families and contribute to expanding the available evidence on vaccination in this population", says study co-leader Pere Soler-Palacín, head of the Paediatrics Service at Vall d'Hebron University Hospital and of the Infection and Immunity in Paediatric Patients group at VHIR.

These results contribute to new data on the immune response and safety of HIPRA's COVID-19 vaccine in adolescents, a population in which it is especially important to generate specific evidence. The study also highlights the importance of collaboration between research centres and companies such as HIPRA to generate scientific evidence and contribute to transferring the advances in biomedical research to society. The participation of adolescents and their families in clinical studies is essential to obtain this evidence and advance in the evaluation of vaccination strategies adapted to paediatric populations, in a context in which SARS-CoV-2 continues to evolve.