Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines have been instrumental in curbing the transmission and widespread impact of the COVID-19 pandemic. With many studies reporting infections and disease complications in children, the efficacy of vaccines in young populations needs extensive research.
About the study
The present study estimated the clinical efficacy of the SARS-CoV-2 receptor-binding domain (RBD) protein vaccines – SOBERANA 02 and SOBERANA Plus – by immunobridging with adult immunogenicity.
The research involved a phase I/II multicenter, adaptive, and open-label study to assess the safety, immunogenicity, and reactogenicity induced by administering two doses of SOBERANA 02 and a third dose of a heterologous SOBERANA Plus vaccines. This study predicted the impact of the vaccines on children aged between three to 11 years and teenagers between 12 to 18 years.
Phase I of the study incorporated 25 children aged 12 to 18 years, followed by the first interim report seven days after vaccination. If the first interim report found no serious adverse effects (AEs), 25 children aged between three to 11 years were incorporated in the study. Then, phase II was started with the incorporation of 150 children aged 12 to 18 years, followed by a second interim report which allowed the inclusion of children aged three to 11 years.
SARS-CoV-2 reverse transcription-polymerase chain reaction (RT-PCR) assay was performed on samples provided by all participants at least 72 hours before vaccination. RT-PCR negative individuals were vaccinated by injecting the dose intramuscularly with the two doses of SOBERANA 02 and the third dose of SOBERANA Plus, administered 28 days apart from each other. A follow-up was scheduled 24, 48, and 72 hours post-vaccination and after 7, 14, and 28 days post each dose.
Collection of serum samples was performed on the day of vaccination prior to administration (day 0) and 14 days post-second and third dose. Peripheral blood mononuclear cells were also collected before vaccination and after the administration of the third dose (day 70).
A quantitative ultramicro enzyme-linked immunosorbent assay (UMELISA) was performed to determine the quantity of anti-RBD immunoglobulin G (IgG) antibodies in the serum samples. Also, a competitive ELISA was conducted to determine the capacity of the antibodies in inhibiting the interaction between RBD and human angiotensin-converting enzyme 2 (hACE2).
The study results showed that in the period from 11 June 2021 to 14 July 2021, a total of 426 children aged between three and 18 years with a median age of 11.3 years participated in the study. Out of the total 426 participants, 306 completed the entire study.
The vaccination scheme showed that over 53% of children experienced at least one AE, with 60% of occurrences in teenagers and 46.3% in young children. There were no reports of severe vaccine-associated AEs (VAAE). The most common AEs included 47.7% reports of local pain, while less than 5% reported other AEs, including 1.1% of individuals who reported fever. Over 90% of the reported AEs were mild and lasted less than 72 hours, while 88.5% of them were vaccine-induced. Notably, AEs were reported more frequently post-first vaccine dose than post-second and third dose.
Prior to vaccination, 97.4% of the participants tested negative for the presence of anti-RBD antibodies. After two vaccine doses of SOBERANA 02, seroconversion was observed in 95% of the participants, with 99.4% in children aged three to 11 years and 91.8% in children aged 12 to 18 years. Post-third dose, seroconversion increased to 100%. Also, the inhibitory capacity of the antibodies in preventing RBD-hACE2 interaction after the administration of two SOBERANA 02 doses was 67.4%, and the same increased to 92.4% post the third heterologous dose.
The neutralizing titers against the SARS-CoV-2 D614G variant in children vaccinated with two SOBERANA 02 doses were higher than in convalescent children, while the third vaccine dose significantly increased the neutralizing titers further. Moreover, 100% of the participants had neutralizing titers against SARS-CoV-2 Alpha and Delta variants of concern (VOCs), while 97.9% had the same against the Beta VOC.
The study findings showed that the immunological results and safety profiles of the SOBERANA 02 and SOBERANA Plus vaccines reported for the present heterologous vaccination scheme in children supported the authorization of emergency use of the vaccines in the younger populations. Researchers believed that vaccinating these populations is crucial in controlling and preventing further transmission of SARS-CoV-2.
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