FILE PHOTO: A sign on an insurance store advertises Obamacare in San Ysidro, San Diego, California, U.S., October 26, 2017. REUTERS/Mike Blake/File Photo

WASHINGTON (Reuters) - The number of people signing up for 2018 Obamacare plans picked up significantly during the fifth week of open enrollment, a U.S. government agency reported on Wednesday, but the number of participants appears to be falling short of last year’s numbers with just over a week of enrollment left.

For the week ended Dec. 2, the U.S. Department of Health and Human Services said 823,180 people signed up for 2018 Obamacare individual insurance in the 39 states that use the federal government website Healthcare.gov. That was up from 504,181 people in the previous week. About 3.6 million people so far have signed up for Obamacare plans using the federal website.

New consumer sign-ups rose to 271,207 from 152,243 during the previous week. An analyst said he expected a 20 percent decline in Obamacare enrollment for 2018.

The Trump administration halved the Obamacare open enrollment period for 2018 to six weeks ending Dec. 15, and cut the healthcare law’s advertising budget by 90 percent. For 2017, more than 9.2 million consumers signed up for insurance plans using Healthcare.gov during the 12-week open enrollment period, which included people who were automatically re-enrolled at the close of the enrollment period.

Based on the government information, enrollment is likely to decline 20 percent in 2018 from 2017, Wall Street analyst Matt Borsch at BMO Capital Markets said in a research report. He projected that the final tally of Obamacare sign-ups, including those who are automatically re-enrolled and those purchasing in states that run their own exchanges, would be less than 10 million, down from 12.2 million in 2017.

Borsch said that despite the lower enrollment, profitability has been up on the exchanges for the three health insurers with the biggest numbers of customers there: Anthem Inc, Centene Corp and Molina Healthcare Inc.

The figures do not include enrollment in Washington, D.C., or the 11 states that run their own enrollment and websites, some of which have enrollment periods that are weeks longer. The subsidized individual insurance market is part of former President Barack Obama’s healthcare law, commonly known as Obamacare.