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Volume 32, Number 12—December 2026

Research Letter

Cross-Protection against Influenza A(H5) Clade 2.3.4.4b Viruses after A(H1N1)pdm09 Infection

Xiangjie Sun, Jessica A. Belser, Zhu-Nan Li, Nicole Brock, Joanna A. Pulit-Penaloza, Troy J. Kieran, Claudia Pappas, Hui Zeng, Jessie C. Chang, Paul J. Carney, Brandon L. Bradley-Ferrell, James Stevens, Min Z. Levine, and Taronna R. MainesComments to Author 
Author affiliation: Centers for Disease Control and Prevention, Atlanta, Georgia, USA

Main Article

Figure 2

Viral titers after A(H5N1) and A(H5N5) challenge in ferrets in a study on cross-protection against influenza A(H5) clade 2.3.4.4b viruses after A(H1N1)pdm09 infection. A, B) Mean viral titers in nasal washes and throat and rectal swab specimens after challenge with H5N1 (A) or H5N5 (B) virus. We assessed statistical differences between preimmune and naive groups at each time point by using 2-way analysis of variance with Sidak’s multiple comparisons test after confirming normality with Shapiro-Wilk test. C, D) Mean viral titers in tissue and blood specimens (log10 PFU/g for tissues or mL for blood) on day 4 postinfection with either H5N1 (C) or H5N5 (D) virus. Symbols indicate individual preimmune or naive animals. Error bars represent SDs. When <3 ferrets had detectable virus, the number positive/3 necropsied ferrets is indicated. When all 3 ferrets in preimmune and naive groups had detectable virus, we assessed differences by using the Mann-Whitney test. NT, nasal turbinates.

Figure 2. Viral titers after A(H5N1) and A(H5N5) challenge in ferrets in a study on cross-protection against influenza A(H5) clade 2.3.4.4b viruses after A(H1N1)pdm09 infection. A, B) Mean viral titers in nasal washes and throat and rectal swab specimens after challenge with H5N1 (A) or H5N5 (B) virus. We assessed statistical differences between preimmune and naive groups at each time point by using 2-way analysis of variance with Sidak’s multiple comparisons test after confirming normality with Shapiro-Wilk test. C, D) Mean viral titers in tissue and blood specimens (log10 PFU/g for tissues or mL for blood) on day 4 postinfection with either H5N1 (C) or H5N5 (D) virus. Symbols indicate individual preimmune or naive animals. Error bars represent SDs. When <3 ferrets had detectable virus, the number positive/3 necropsied ferrets is indicated. When all 3 ferrets in preimmune and naive groups had detectable virus, we assessed differences by using the Mann-Whitney test. NT, nasal turbinates.

Main Article

Page created: October 09, 2026
Page updated: November 10, 2026
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