英语语法分析

Whether this reflects the persistence of pre-existing immunity at the time of revaccination or lower rates of revaccination in the study populations cannot be determined.

这是因为再次接种时前次的免疫性仍然存在，抑或是因为在研究人群中再次接种率较低，对此目前尚无定论。

Methods a retrospective investigation method was used to analysis the epidemic situation of pulmonary tuberculosis before and after BCG revaccination and prophylactic chemotherapy.

采取回顾性调查的方法，对BCG复种及预防性服药停止前后的肺结核疫情进行分析。

Therefore, the two indicators used as reflecting tuberculosis infection and onset after BCG revaccination termination were both not higher and even lower than the BCG revaccination group.

由此可见，用于反映停止BCG复种组结核感染与发病的两项主要指标均不高于甚至低于未停BCG复种组。