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What were the durability of immune responses (antibody and T-cell) after Janssen vaccination at 24+ months?
Executive summary
Available reporting shows Janssen’s Ad26.COV2.S vaccine produced antibody and T‑cell responses that were durable for months but the reviewed sources do not report direct measurements at "24+ months." Multiple studies and summaries describe stable humoral and cellular responses out to about 8–12 months and real‑world effectiveness claims beyond that, but explicit 24‑month immunologic data are not found in the provided sources [1] [2] [3] [4].
1. What the peer‑reviewed and trial literature says about durability (months, not years)
Early clinical and follow‑up trial reports and journal summaries show Janssen’s single‑dose Ad26.COV2.S induced neutralizing antibodies and T‑cell responses that persisted with minimal decline for at least 8 months after vaccination: the NEJM correspondence and coverage reported durable humoral and cellular responses at eight months [1] [5]. Company‑released summaries and press materials citing peer‑reviewed NEJM data similarly state antibody and T‑cell responses were “strong and stable at eight months” [2]. A broader review of vaccine durability compared multiple platforms and concluded Ad26.COV2.S titers appear lower initially but more stable over time compared with mRNA vaccines [6].
2. Real‑world cohorts and longer follow‑up claims (up to ~12 months in available sources)
Observational cohort work in sub‑Saharan Africa reported persistent anti‑spike IgG responses to a single Janssen dose up to 12 months in a Ugandan cohort, describing “robust and persistent” antibody levels and noting modest breakthrough infection rates in that group (13% in the cited cohort) [3] [7]. These regional cohort studies emphasize sustained antibody detection and argue logistical advantages of a single‑dose regimen where repeat dosing is difficult [3].
3. How antibody and T‑cell durability are characterized differently
Sources emphasize two patterns: neutralizing antibody titers for Ad26.COV2.S are typically lower than mRNA‑induced peaks but decline more slowly, while cellular (T‑cell) responses remain comparatively stable for months after vaccination [6] [1]. The NEJM trial design included planned immunogenicity follow‑up at 6 months and 1 year, indicating investigators expected to measure medium‑term durability, but the documents available here report results mainly to 8–12 months [5].
4. Manufacturer and public‑health framing: protection claims vs. measured immune markers
Johnson & Johnson / Janssen communications highlight “durable humoral and cellular immune responses” and cite real‑world and trial data asserting long‑lasting immune memory and increased neutralization of variants over time; their press releases reference four‑ to twelve‑fold antibody increases after boosters and claim strong long‑lasting protection in Phase 3 and real‑world analyses [2] [4]. Public health documents (WHO, CDC) note that Janssen can be followed by other vaccine types for boosting and discuss recommended intervals, implying immune memory can be augmented but those guidance documents do not provide explicit 24‑month immune readouts in these sources [8] [9].
5. What the sources do not show — the 24+ month gap
None of the provided sources include explicit immunologic measurements (neutralizing antibody titers or T‑cell assays) at 24 months or beyond after Janssen vaccination. The materials report durability up to eight months in trial correspondence, up to 12 months in select cohort studies, and broader effectiveness claims in press releases, but do not present peer‑reviewed 24‑month antibody or T‑cell kinetics or direct comparisons that extend to two years [1] [5] [3] [2] [4]. Therefore, specific statements about immune levels at 24+ months are not supported by the supplied reporting.
6. Competing interpretations and implicit agendas
Academic and independent reviews frame Ad26.COV2.S as producing a “middling but durable” immune response compared with mRNA vaccines — lower peak titers, slower decline — which is a neutral scientific characterization [10] [6]. Janssen/Johnson & Johnson press statements emphasize favorable long‑lasting protection and booster responses; corporate messaging seeks to highlight product durability and booster benefits [2] [4]. Cohort studies in low‑ and middle‑income settings underscore programmatic advantages of a single‑dose vaccine where follow‑up is challenging [3], a framing that carries public‑health policy implications.
7. Bottom line for your question
Available sources document durable antibody and T‑cell responses to Janssen’s Ad26.COV2.S out to about 8 months in trial data and up to ~12 months in at least one cohort study, and they frame cellular immunity as relatively stable compared with mRNA vaccines [1] [2] [3] [6]. However, the sources provided do not include immunologic measurements or peer‑reviewed reports specifically at 24+ months after Janssen vaccination; any claim about 24‑month antibody or T‑cell levels is not found in the current reporting [1] [5] [3].
If you want, I can search for published 24‑month immunogenicity studies or regulatory updates beyond these sources.