The number of new customers signing up for health insurance through the Covered California exchange jumped 23 percent during the first two weeks of open enrollment compared with the same period last year, state officials said Thursday.

About 48,000 new customers signed up for subsidized health plans between Nov. 1 and Nov. 14 — up from 39,000 during the same period in 2016.

“What’s most stunning is that the number of people enrolled so far is so much higher than those enrolled the year before,” said Nadereh Pourat, research director at the UCLA Center for Health Policy Research. She noted that the Trump administration has cut back on advertising, and attempts to repeal the Affordable Care Act have created confusion.

“I’m guessing a lot of people are enrolling rapidly because they’re trying to get it while they still can,” she said.

The Covered California exchange, created by the Affordable Care Act and in its fifth enrollment season, enables people who don’t get insurance through their employers or Medi-Cal to get coverage. Premiums for 2018 are up 12.5 percent on average compared with 2017, but most people on the exchange receive federal subsidies, and for many of them, those are also higher this year.

Covered California did not yet have figures for how many people renewed their existing health plans in early November, and it is unclear how many people may drop their insurance plan before the open enrollment period ends Jan. 31. At 12 weeks, California’s open enrollment period is twice as long as open enrollment for the 39 states that use the federal insurance exchange HealthCare.gov.

An increase in new customers does not necessarily indicate a net gain in overall enrollment because attrition on the exchange is common. Some people get new jobs and receive health insurance through work, enroll in Medi-Cal, or stop buying plans through the exchange for other reasons.

Peter Lee, executive director of Covered California, said in a statement that while exchange officials are “encouraged by (the) early results, we will continue to work hard to get the word out so consumers know they have until Jan. 31 to sign up for coverage.”

Signups on the federal exchange are also up. During the first two weeks of open enrollment, nearly 1.5 million Americans enrolled in insurance through HealthCare.gov — up 46 percent compared with roughly 1 million during the same period in 2016. Those figures include new signups and renewals. The number of new customers buying plans rose 40 percent, from 250,000 to nearly 346,000 people, according to the Centers for Medicare and Medicaid Services.

Experts said the jump in federal signups is steeper than that in California because the state exchange had already enrolled a large percentage of the uninsured population in prior open enrollment periods.

The Affordable Care Act has survived repeated efforts this year by President Trump and congressional Republicans to repeal it or scale it back. The GOP attempts resurfaced this week, with Senate Republicans seeking to eliminate the health law’s individual mandate — the requirement to buy health insurance or face a tax penalty — as part of their proposal to overhaul the nation’s tax code. Eliminating the individual mandate would result in 13 million fewer Americans having health insurance by 2027, including 730,000 Californians on the state exchange and 1.7 million Californians total, according to estimates from the Congressional Budget Office and UC Berkeley Labor Center.

The Department of Health and Human Services drastically cut marketing dollars to advertise the federal exchange. But insurance agents and brokers — whose efforts have historically been the most effective way to sign up customers — and a website feature that allows customers to click a button and receive a call from an agent are both helping to boost enrollment, said Timothy Jost, a professor emeritus of health law at Virginia’s Washington and Lee University who writes the blog Health Affairs.

“So there are some countervailing forces to the cutting back they’ve been doing,” Jost said.

But the early rush of federal signups may not continue at the same pace because the federal government cut its open enrollment period in half to six weeks, Jost said. In 2016, 9 million people signed up for insurance through HealthCare.gov during open enrollment. Getting to a comparable number in half the amount of time may be a challenge, even though the pace of signups tends to pick up as open enrollment continues.

“Getting from 1.5 (million) to 9 (million) in four weeks is a pretty tall effort,” Jost said. “Getting there is going to be a stretch.”

The creation of Covered California and the expansion of Medi-Cal, the insurance program for the poor, are the two primary ways California has lowered its uninsured rate significantly since the Affordable Care Act went into effect in 2014. About 3.7 million more Californians are enrolled in Medi-Cal as a result; 1.3 million are enrolled in plans through the exchange.

Catherine Ho is a San Francisco Chronicle staff writer. Email: cho@sfchronicle.com Twitter: @Cat_Ho

23

Percent increase in customers signing up through Covered California compared with last year

12.5

Average percent increase in premiums compared with last year

46

Percent increase in customers enrolling through HealthCare.gov, the federal exchange