Since its first incursion in 2019, African swine fever (ASF) has remained a constant threat to the Vietnamese swine industry. The nationwide commercialization and implementation of live‐attenuated vaccines (LAVs), alongside depopulation‐repopulation efforts, necessitate a critical assessment of whether these strategies have driven inadvertent changes in circulating African swine fever virus (ASFV) strains. In this study, molecular surveillance of ASFV core genes was conducted in pigs from non‐vaccinated farms across Central and Southern Vietnam, comparing strains before and after LAVs’ introduction. The results confirmed spillover and ongoing field circulation of LAV‐related strains and revealed a marked increase in genetic diversity, encompassing both vaccine‐like and novel wild‐type microvariants in the post‐vaccine commercialization phase. Notably, these microvariants harbored non‐synonymous single‐nucleotide polymorphisms (SNPs) and large segmental deletions within the EP153R-EP402R gene, suggesting potential alterations in viral function. Most compellingly, a unique 15‐AGACCAGCAACAAAC‐nucleotide repeat in the E183L gene resulted in a five‐amino‐acid insertion (Arg‐Pro‐Ala‐Thr‐Asn) in the p54 protein, serving as a key marker for Vietnamese strains. Initial in silico analysis indicated that this novel p54 protein contained a longer α‐helix structure, which could influence viral movement and interactions with host cells. Overall, these subtle yet significant genetic shifts imply that ASFV might be rapidly evolving intra‐host under selective pressure from widespread immunization and/or diverse introduction sources during repopulation, potentially enabling it to evade the host immune system. This highlights the essential need for robust biosecurity protocols, stringent regulatory oversight of LAV deployment, and the required genetic surveillance. For diagnosis and management, the urgent development of reliable DIVA (Differentiating Infected and Vaccinated Animals) tools and real‐time, adaptable molecular identification methods, coupled with a vaccination‐tracking system, is necessary for accurate and sustained ASF control.

Porcine epidemic diarrhea virus (PEDV) is an economically important pathogen of swine, causing severe diarrhea in neonates with high morbidity and mortality. Vaccination is a key strategy for PEDV control, but optimizing regimens based on herd status is essential for improving immunity and protection. This study evaluated immune responses to different vaccination protocols using a PED replicon vaccine (PED-RP) in Thai swine farms with varying PED statuses. Two field trials were conducted: Experiment 1 (n = 120) on a PED-negative farm used a killed vaccine followed by PED-RP, while Experiment 2 (n = 42) on a PED-positive farm used a modified-live vaccine (MLV) followed by PED-RP. In Experiment 1, gilts boosted with PED-RP during gestation showed significantly higher colostrum IgA levels compared to those receiving two doses of the killed vaccine. In Experiment 2, priming with MLV followed by PED-RP resulted in increased neutralizing antibody titers and seropositivity, outperforming the MLV-only regimen after acclimatization. These findings suggest that using PED-RP as a booster can enhance serum and lactogenic immunity, providing a promising strategy for improving immune responses in both PED-negative and PED-positive herds. The study highlights the importance of tailored vaccination strategies to optimize herd immunity and protect piglets from PEDV.

Porcine reproductive and respiratory syndrome virus 2 (PRRSV-2) remains one of the most important transboundary pathogens affecting swine production in Vietnam; however, it remains poorly understood how long-term evolutionary dynamics were impacted by the African swine fever (ASF) epidemic, a period of time where swine population demographics and movement were heavily perturbed. We investigated the molecular epidemiology, evolutionary history, and phylogeographic dynamics of PRRSV-2 circulating in Vietnam between 2007 and 2024 by integrating 366 Vietnamese ORF5 sequences with a globally curated lineage reference. Maximum-likelihood phylogenetic, Bayesian phylodynamic, and discrete phylogeographic analyses revealed that the Vietnamese PRRSV-2 population underwent substantial reshaping after the ASF epidemic, shifting from a predominantly endemic sub-lineage L8E population to a genetically diverse viral community comprising multiple established and newly emerging sub-lineages. Despite these epidemiological changes, the endemic sub-lineage L8E population maintained a relatively stable evolutionary rate across the pre- and post-ASF periods, suggesting that ASF reshaped viral population structure rather than intrinsic evolutionary dynamics. Two previously unclassified viral clusters circulating in Vietnam and Thailand fulfilled all criteria for formal designation and were recognized as the novel sub-lineages L1M and L10B by the International PRRSV-2 Nomenclature Consortium. Phylogeographic reconstruction further demonstrated contrasting transmission patterns among major sub-lineages, including long-term endemic persistence of L8E, repeated unidirectional introductions of sub-lineages L1M and L10B from Thailand, and bidirectional transpacific dissemination of sub-lineage L1A linking Southeast Asia and North America. Collectively, these findings demonstrate that the ASF epidemic coincided with a fundamental reshaping of the PRRSV-2 epidemiological landscape in Vietnam while revealing Southeast Asia as an active center of ongoing viral diversification. This study provides an updated evolutionary framework for PRRSV-2 surveillance and highlights the importance of continuous genomic monitoring and regional collaboration for the early detection and control of emerging transboundary variants.