Experimental reproduction numbers disentangle vaccine effects on susceptibility and infectiousness during H5N1 transmission in geese
Year: 2026
Type: preprint
Abstract: Vaccination against high pathogenicity avian influenza virus (HPAIV) is increasingly used to protect poultry, but vaccine performance is commonly inferred from clinical protection and virus shedding rather than measured transmission. We asked whether reproduction numbers from controlled transmission experiments can quantify how vaccination changes infection dynamics in virus-exposed geese, i.e. susceptibility and infectiousness. Domestic geese were prime-boost vaccinated with an H5 clade 2.3.4.4b RNA-amplicon vaccine and challenged with homologous HPAIV H5N1. Replicats of seeder-sentinel groups represented transmission among unvaccinated animals, to vaccinated contacts, and from vaccinated breakthrough-infected animals. Vaccinated directly challenged geese remained clinically protected although all became productively infected. Estimated reproduction numbers were R 0 =4.7 (95% CI, 2.8-8.0) among unvaccinated geese, R s =2.6 (1.6-4.5) for transmission to vaccinated contacts, R i =3.7 (2.0-6.8) for transmission from vaccinated infected geese, and R vacc =2.0 (0.8-4.9) for a fully vaccinated population. Vaccination reduced transmission but, under these experimental exposure conditions, did not reduce the point estimate for R vacc below one. Even though vaccinated infected geese shed substantially less viral RNA, infectiousness was sufficient to sustain transmission in vaccinated geese, indicating that RNA shedding alone may not reliably predict efficacy of transmission reduction. Experimental reproduction numbers therefore provide a direct population-level complement to conventional vaccine testing protocols and can separate effects on susceptibility from effects on onward transmission. Author Summary Vaccines against high pathogenicity avian influenza are usually evaluated by asking whether they prevent disease and reduce the amount of virus shed by infected birds. For disease control, however, it is equally important to know whether vaccination prevents onward transmission. We used domestic geese infected with H5N1 avian influenza virus to test whether this effect can be measured directly in small transmission experiments. By co-housing vaccinated and unvaccinated infected birds with vaccinated or unvaccinated contact birds, we estimated reproduction numbers for different transmission circumstances. Vaccination fully protected geese from clinical disease and reduced viral RNA shedding, but it did not prevent infection or transmission. The estimated reproduction number fell from 4.7 among unvaccinated geese to 2.0 for transmission to a fully vaccinated population, although the confidence interval was wide. Notably, the reduction in viral RNA shedding overestimated the effect on infectiousness. Thus, shedding alone may overstate how strongly a vaccine limits transmission. Directly estimating transmission can therefore add important information to conventional vaccine- efficacy studies and may improve comparisons between vaccines.
Language: English
Subfield: Epidemiology
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W7208722082