On a 1989 sabbatical he met Virologist Jian Zhou, and the two considered the Problem of developing a vaccine for HPV – a virus that cannot be cultured without living tissue. Frazer convinced Zhou to join him, and in 1990 they began to use molecular biology to synthesize particles in vitro that could mimic the virus. In March 1991 Zhou's wife and fellow researcher, Xiao-Yi Sun, assembled by Zhou's instructions two proteins into a virus-like particle (VLP), resembling the HPV shell, from which HPV vaccine would ultimately be made. (The vaccine completely protects unexposed women against four HPV strains responsible for 70% of cervical cancers, which kill about 250,000 women annually.) Frazer and Zhou filed a provisional patent in June 1991 and began work on developing the vaccine within UQ. To Finance clinical trials, Australian medical company CSL, and later Merck, were sold partial patents. (CSL has the exclusive license to sell Gardasil in New Zealand and Australia, Merck the license elsewhere.) GlaxoSmithKline independently used the same VLP-approach to develop Cervarix, under a later US patent, licensing Frazer's intellectual property in 2005.