Invited Commentary: Attendance and Absence as Markers of Health StatusThe Example of Active and Passive Cigarette Smoking Vaping Q&A: Johns Hopkins Expert on E Cigarettes and Tobacco Alternatives Johns Hopkins Bloomberg School of Public Health Johns Hopkins Bloomberg School of Public Health Epidemiology Department Baltimore MD Are E Cigarettes and Vapes The Same Thing? Is Vaping Safer Than Smoking? Let's Talk Science A Closer Look at the 34 FDA Authorized E Cigarettes