Immunity and vaccination against SARS-CoV-2 in children: where are we in 2025?

Medical Review (Med. pregled), 2025, 61(5), 12-19.

P. Velikov

Department of Infectious Diseases, Parasitology and Tropical Medicine, Medical Faculty, Medical University – Sofia; Specialized Hospital for Infectious Diseases and Parasitology „Prof. Ivan Kirov“

Abstract. Objective: To synthesise current evidence on the paediatric immune response to SARS-CoV-2, the effectiveness and safety of authorised COVID-19 vaccines in children, and international immunisation recommendations, in order to develop practical recommendations for Bulgaria. Methods: A structured literature search was conducted in PubMed/MEDLINE, Web of Science and official reports issued by international organizations. Eligible publications in Bulgarian, English or French that directly addressed the topic were screened and analysed. Key findings: Children mount an early innate response and maintain IgG antibodies for 12-18 months, yet neutralising activity declines threeto five-fold against the Omicron sub-lineages JN.1, KP.3 and LB.1. The XBB.1.5- and JN.1-adapted mRNA vaccines Comirnaty® and Spikevax® provide ≥ 80% protection against symptomatic infection and ≥ 95% against hospitalisation; post-vaccination myocarditis/pericarditis occurs in < 3 per 100,000 doses lower than the risk after natural infection. National vaccine coverage in Bulgaria remains below 35%, largely due to misinformation and mistrust, resulting in postponed or missed immunisations. Conclusions: Natural immunity in children is insufficient for durable control of rapidly evolving SARS-CoV-2 variants. A single variant-adapted booster for all children ≥ 5 years, shortened primary schedules for those aged 6 months-4 years, and annual revaccination of high-risk groups are strongly recommended. Urgent measures are needed to promote vaccination – especially in vulnerable communities and to implement a nationwide campaign to overcome vaccine hesitancy.

Key words: children, SARS-CoV-2, COVID-19 vaccine

Address for correspondence: Petar Velikov, ORCID iD: 0000-0002-7436-4064