{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,5,4]],"date-time":"2026-05-04T03:14:09Z","timestamp":1777864449029,"version":"3.51.4"},"reference-count":44,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,4,30]],"date-time":"2026-04-30T00:00:00Z","timestamp":1777507200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Immunol."],"abstract":"<jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>Adults aged \u226560 years face elevated risks of severe COVID-19 and long COVID. Although inactivated SARS-CoV-2 vaccines are safe and effective, critical gaps remain regarding optimal booster timing, durability of immune responses, and protection against emerging variants in this vulnerable population.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>In this prospective cohort study in Zhejiang Province, China, 450 adults aged \u226560 years were randomized to receive an inactivated SARS-Cov-2 vaccine (CoronaVac or Covilo) under three dosing schedules. Neutralizing antibody titers, SARS-CoV-2-specific IgG, and variant-specific neutralization were evaluated using serum samples collected at multiple timepoints. Safety outcomes included local and systemic adverse reactions and long COVID symptoms.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>Participants (age: 60\u201380 years; 50.9% male) with balanced baseline demographics were stratified into six subgroups by vaccine type and schedule (S1\/S2\/S3; n=75 each; all P&amp;gt;0.05). Adverse reaction incidence was low (0.0%\u20138.0%), with CoronaVac-S3 recipients experiencing significantly more local reactions than Covilo-S3 recipients (8.0% vs. 0.0%; P\u00a0=\u00a00.0124). Immunogenicity varied markedly at 1 month post vaccination, with the highest geometric mean titers (GMTs) of neutralizing antibodies in both S3 groups (Covilo: 57.2; CoronaVac: 59.4; P&amp;lt;0.001 vs. respective S1\/S2 groups), and CoronaVac-S1 inducing higher GMTs than Covilo-S1 (21.8 vs. 15.4; P\u00a0=\u00a00.009). At 12 months post vaccination, GMTs remained highest in Covilo-S3 (9.9), while CoronaVac-S2 exceeded Covilo-S2 (8.0 vs. 5.1; P\u00a0=\u00a00.021). Covilo-S2 and -S3 were superior to their CoronaVac counterparts in inhibition against the wild-type strain and Delta variant at 1 month post vaccination (all P&amp;lt;0.05). Multivariate analysis identified male sex as a protective factor against COVID-19 symptoms, long COVID, and fatigue (odds ratios &amp;lt;0.5 and P&amp;lt;0.05 for all).<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusions<\/jats:title>\n                    <jats:p>A third booster of inactivated SARS-CoV-2 vaccine administered within 2\u20136 months of the second dose is safe and significantly boosts humoral immunity in adults \u226560 years. The three-dose Covilo regimen and a 6-month dosing interval optimized immunogenicity and were associated with the lowest risks of COVID-19 symptoms and long COVID, highlighting the importance of vaccine-specific and interval-adjusted booster strategies for older populations.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.3389\/fimmu.2026.1813716","type":"journal-article","created":{"date-parts":[[2026,4,30]],"date-time":"2026-04-30T05:42:02Z","timestamp":1777527722000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Safety, immunogenicity, and long COVID outcomes following inactivated COVID-19 vaccine boosters in elderly Chinese: a prospective cohort study"],"prefix":"10.3389","volume":"17","author":[{"given":"Rongrong","family":"Dai","sequence":"first","affiliation":[{"name":"Department of Public Health and Preventive Medicine, Wuxi School of Medicine, Jiangnan University","place":["Wuxi, 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