The primary objective of this study was to evaluate the effects of a single breakthrough infection on immune responses to inactivated whole-virus vaccination, while excluding the influence of prior undocumented asymptomatic infection. Neutralizing antibody titers in infection-naïve individuals who had received three doses of inactivated COVID-19 vaccines were very low against a range of tested pseudoviruses. In contrast, conva lescent individuals who experienced a single breakthrough infection with BA.5 after receiving two or three doses of inactivated vaccines exhibited high neutralizing titers against variants that emerged prior to BQ.1. However, neutralizing activity was substantially reduced against post-BQ.1 variants, particularly the XBB sublineages. Notably, two convalescent individuals demonstrated relatively high neutralizing potency against all 31 tested viruses, including HK.3 and JD.1.1. To the best of our knowledge, this is the first report demonstrating that broadly potent neutralizing antibody responses against all tested viruses can be elicited following a single BA.5 breakthrough infection.