The problem is, at the time that this is all known in the 1980s, vaccine technology could only fit in a few serotypes per injection, without causing an enormous immune response.

问题是， 在 1980 年代这一切都为人所知的时候，疫苗技术每次注射只能适应几种血清型，而不会引起巨大的免疫反应。