What motivates state-sponsored vaccine misinformation campaigns, given clear scientific evidence of vaccines' efficacy? We explore this issue through the lens of state-owned presses published in mainland China and in Hong Kong. We first collect an original database of media reports on both Western and Chinese vaccines from 16 Chinese-language media publications based in mainland China, Hong Kong, and Taiwan. We find that the quantity of coverage of Western vaccines by mainland state-owned media outlets to be much less than their coverage of Chinese vaccines, reflecting the unavailability of Western vaccines in mainland China. However, applying a dictionary-based sentiment analysis, we find that state-owned presses in mainland China still portrayed Western vaccines negatively. In Hong Kong, where there is direct competition between Chinese and Western vaccines, we find that state-owned presses gave high coverage of Western and Chinese vaccines but greater negative coverage of Western vaccines. These findings are consistent with a Chinese ``vaccine nationalism" policy designed to nurture the domestic biotechnology sector.