Two more people have died from a mysterious lung illness linked to vaping, bringing the total number of deaths in the US to 11.
Georgia health officials reported the first death in the state from a vaping-related illness on Wednesday (local time).
The doctors involved in this case said the patient did not vape THC, but had a history of heavy nicotine vaping.
Later the same day, Florida also reported its first death from a vaping-related illness in the state.
The previous nine deaths occurred in Kansas, Missouri, Indiana, Minnesota, California, Illinois and Oregon.
The Centres for Disease Control is currently investigating 530 reported cases of severe lung illness related to vaping as of Thursday (local time).
The agency has still not determined the ingredient in e-cigarettes is causing the mysterious illness, but that the cases have occurred in people using nicotine-based e-cigarettes and THC, the active ingredient in marijuana, e-cigarettes.
The CDC said symptoms include cough, shortness of breath, fatigue, chest pain, nausea, vomiting and diarrhoea, which can worsen over time.
New Australian research published on Monday reveals flavoured e-cigarettes can kill lung cells.
The study's lead researcher, Miranda Ween from the School of Medicine at Adelaide University, told RNZ the study was investigating whether or not the same flavour, (apple was used for the research), bought from different suppliers could have different effects.
"What we found was that each of the flavours actually had very different chemicals in it and that they were all capable of killing airway cells and affecting immune cells even when there wasn't any nicotine in it."
Some of the damage to lung cells can be repaired by the body but it also introduces the possibility there would be errors in the repair process, Ween said.
The research was a first step and the next stage for her team would be to isolate which particular chemicals were causing harm.
In light of the research becoming available, governments will be interested in regulation, she said.
The US is looking at restricting certain flavours in e-cigarettes, and the rest of the world will be watching what happens and may look at following suit, she said.
New Zealand's director-general of health, Dr Ashley Bloomfield, said last week the Government is preparing a bill on vape regulation, which will limit flavours to tobacco, menthol and mint.
It was possible safer vapes could be developed in the future but it would take a lot of research to achieve this, Ween said.
Most of the data on vaping, including theirs, showed vaping was probably less dangerous than smoking but most are short-term studies so the long-term effects aren't understood.
If e-cigarettes were used by former smokers in the short term they would probably be safe but the goal was to give up altogether.
Ween said people who are trying to quit smoking should stick to traditional nicotine replacement therapies.
- additional reporting RNZ