Preparation and evaluation of a novel, live, attenuated influenza H1N1 vaccine strain produced by a modified classical reassortment method.

Live attenuated influenza vaccine (LAIV)-based Vero cells could provide a better choice to control and prevent influenza virus infections. This study used the human influenza virus A/Yunnan/1/2005Vca(H3N2) (YN/05Vca) as a donor strain. YN/05Vca has a double phenotype of cold adaption (ca) and Vero cell adaption (va). The parental virus strain used was the wild-type A/Solomon Islands/3/2006 (H1N1) (SI/06wt). The study employed the modified classical reassortment method to generate a new virus strain. After co-infection of Vero cells, some different sub-types of the reassorted viruses were generated randomly. Then, the specific anti-serum (anti-YN/05Vca) could combine with and neutralize the donor virus, and the original parental virus could not grow in Vero cells at a low temperature until it was re-structured with the meaningful gene fragment from the donor virus in Vero cells. According to the plaques and RT-PCR results, a new monoclonal strain of Vero cell cold adaption virus was screened: SI/06Vca. After immunological and biological identification, this new strain virus could be used as a seed bank for LAIV, which has maintained surface antigenicity with SI/06wt. Consequently, this new Vero cell cold adaption virus SI/06Vca could be used for large-scale vaccine production with sufficient safety and efficacy, as confirmed by animal experiments with mice and ferrets.