Live-attenuated African swine fever vaccine HLJ/18-7GD is safe in pregnant sows with no impact on reproductive performance or offspring health at a field farm.

African swine fever (ASF) continues to pose a threat to the global pig industry. Previously, we generated a Georgia-07-like genotype II African swine fever virus (ASFV)-based gene-deleted live vaccine (HLJ/18-7GD) and demonstrated that it is safe for pigs and pregnant sows and effective against the parent virus in the laboratory. Here, we report a systematic field safety assessment of HLJ/18-7GD in 201 sows and their offspring across two parities in a real-world farm scenario performed over more than 11 months. Pregnant sows inoculated with HLJ/18-7GD presented no disease signs or adverse reactions and no changes in gestational status or reproductive performance. Inoculation of sows with HLJ/18-7GD did not affect the health, growth or fattening of first- or second- parity offspring. HLJ/18-7GD was detected in inoculated sows and some first-parity piglets but not in second-parity piglets. The vaccine replicated at low levels in sows and their offspring and was cleared in sows by 84 days post inoculation and at age 56 days in first-parity piglets. These data further demonstrate that HLJ/18-7GD is safe for pregnant sows and their offspring, providing strong evidence that the development of gene-deleted live attenuated vaccines is a feasible strategy for obtaining safe and efficacious vaccines against ASF.