"Subsequent studies have found no proof that the vaccine is connected to autism, though some parents are still wary of the shot."

有些家长怀疑研究者和制药商勾结，故意证明疫苗和自闭没有联系。不知这种可能性有多大？

似乎自从六十年代以来，自闭症发病率持续增高，现在发病率也到了惊人的地步。有什么客观原因吗？