Việt Nam has recorded new cases of mild Omicron BA.5 variant and experts are worried it could become more and more predominant. To better understand the effectiveness of vaccination against COVID-19, Phạm Quang Thái, head of the northern regional office of the National Expanded Programme on Immunisation (NEPI) talks to Sức khoẻ&Đời Sống (Health and Life) online newspaper about the issue