ATLANTA – Last year registered the fewest number of U.S. adult smokers, with the national smoking rate plummeting to 15%, a 2% drop over 2014 and the largest single-year decline since 1993, according to a new Centers for Disease Control and Prevention report, CBS News reports.

While the smoking rate among U.S. adults has been on the decline in recent years, it typically only decreased 1 point or less annually. The last time the smoking rate registered more than 1% was between 1992 and 1993 when it fell 1.5%, according to Brian King of the CDC.

Released yesterday, the statistic is based on a national study the government uses to measure for health-related trends. The agency doesn’t have any clear idea as of yet to explain the 2% drop, nor does the CDC know whether the smoking rate will continue to fall this year. “We’d expect continued declines in smoking, as we’ve seen in the past 50 years. But it’s hard to say what [the] future holds,” King said.

Experts have posited that the downturn in smoking can be attributed to anti-smoking campaigns, smoking bans and higher cigarette taxes. It’s likely that the growing popularity of electronic cigarettes may be playing a part as well.

Earlier this month, the U.S. Food and Drug Administration issued deeming rules that extended the agency’s authority to all tobacco products, including e-cigs, cigars, hookah tobacco and pipe tobacco. FDA’s new regulations also restrict the sale of e-cigarettes to those under the age of 18. In March 2014, NACS issued a statement of position that encourages stores selling e-cigarettes to adopt as a best practice a policy of treating these products as age-restricted, subjecting them to the same age-verification procedures as those applicable to tobacco products. The new regulations are effective 90 days from the date of publication of the final rule.