I spoke too soon- it appears htose of us who only partially switch to Esmoking are still at quite increased risk of smokign related death- oh well:
3.4 Dual use. Smokers may take some time to switch completely from tobacco to
nicotine smoking. As long as they continue to smoke even a few cigarettes a day their
risk of dying early remains excessive. (The risk of smoking even 1-4 cigarettes a day
carries a 60% excess risk of dying early. Smoking 5-9 cigarettes a day doubles the risk of
dying early, compared with never smoking2). In particular their excess risk of heart attack
will not diminish substantially until they quit tobacco smoking entirely.