I think there might have been less than four hundred members when I joined (could be remembering wrong).
There tends to be a spurt when a big media channel reports on
vaping, that happened with UK members when the BBC did an article. There has been a lot of coverage in the US and it's becoming fairly constant so the influx of US people seems steady now.
New Year saw a lot of new members - probably trying to follow new year resolutions to quit smoking. Then when the
tobacco taxes were raised significantly in the US I think that encouraged a lot of people to look for alternatives.