The first case was reported at the end of March but authorities have still not identified the chemicals that are causing the illness.
It also remains unclear if all cases are the same kind of injury.
But Prof John Newton, of Public Health England, said: “We are as certain as ever that e-cigarettes are far less harmful than smoking.”
The outbreak does not appear to be linked to long-term use of nicotine e-cigs, which have been used in the US for over ten years.
Officials there instead believe illicit products containing THC – the psychoactive component of cannabis – are to blame.