Human infections caused by avian influenza A(H7N9) viruses have raised concerns of a pandemic. The capability of the current stockpiled A(H7N9) vaccines to induce cross-protective, non-neutralizing functional antibodies against antigenically drifted A(H7N9) viruses has not been evaluated before. Here we show that vaccination with either MF59- or AS03-adjuvanted inactivated A(H7N9) vaccines elicited robust, cross-reactive ADCC-mediating and neuraminidase-inhibiting functional antibodies against the antigenically drifted A(H7N9) viruses that emerged recently during the 5th wave outbreak in China, including a highly pathogenic A(H7N9) human isolate. Such cross-reactive humoral immunity may provide vital first-line defense against fatal outcomes in case of a A(H7N9) pandemic.