Washington Gov. Jay Inslee said the state has a "long ways to go" as it marks the one-year anniversary of the first U.S. case of COVID-19 being discovered in the state of Washington.

"We were hit the first and hardest," Inslee said during a press briefing Thursday. "Our recovery for the pandemic is progressing, and we have a long ways to go and we need to continue to learn from what we have experienced."

Since that first diagnosis, Washington state has reported 296,087 confirmed and probable COVID-19 cases as well as at least 4,065 deaths from the disease.

If the state "made different decisions," there could have been as many as 8,000 more people who died, Inslee said.

On the vaccination front, Washington state is administering on average more than 16,000 doses of COVID-19 vaccines per day, with plans to open four mass-vaccination sites next week, according to the governor.

Amazon will also open a one-day pop-up clinic in Seattle on Sunday, with the aim of administering 2,000 vaccines, Inslee said.

The governor urged residents to "remain diligent" amid the vaccine rollout.

"If we deviate from that course, we will have thousands more deceased Washingtonians in the months to come and that's just a hard fact," he said.

-ABC News' Michelle Mendez contributed to this report

New COVID-19 cases and deaths reported in the United States decreased substantially in week-to-week comparisons, according to a Health and Human Services memo obtained by ABC News Thursday.

Twenty-six states are in a downward trajectory of new cases, the memo stated.

The number of new cases confirmed from Jan. 15 to 21 decreased 20.4% compared to the previous seven-day period. The number of deaths decreased 9.2% during that time.

The national test-positivity rate dropped to 10.6% from 13.1% in week-to-week comparisons.

The percentage of hospitals with more than 80% of their intensive care unit beds filled and the percentage of inpatients with COVID-19 have also decreased slightly, according to HHS.

ABC News' Josh Margolin contributed to this report.

A Texas doctor is accused of stealing a COVID-19 vaccine vial that contained nine doses, according to Harris County District Attorney Kim Ogg.

Dr. Hasan Gokal of Harris County Public Health allegedly took the vial while working at a county vaccination site on Dec. 29. He was fired and has been charged with theft by a public servant, Ogg said.

"He abused his position to place his friends and family in line in front of people who had gone through the lawful process to be there," Ogg said in a statement. "What he did was illegal and he'll be held accountable under the law."

Gokal's lawyer, Paul Doyle, told Houston ABC station KTRK in a statement that the reason he took the vial was because the doses were going to expire.

"Dr. Gokal is a dedicated public servant who ensured that COVID-19 vaccine dosages that would have otherwise expired went into the arms of people who met the criteria for receiving it," Doyle said. "Harris County would have preferred Dr. Gokal let the vaccines go to waste and are attempting to disparage this man's reputation in the process to support this policy. We look forward to our day in court to right this wrong."

Dr. Anthony Fauci, chief medical adviser to U.S. President Joe Biden, said his “best-case scenario” is getting 85% of Americans vaccinated by the end of the summer.

"If we get 70% to 85% of the country vaccinated, let’s say by the middle of the summer, I believe by the time we get to the fall, we will be approaching a degree of normality," Fauci, who is also the director of the National Institute of Allergy and Infectious Diseases, told reporters at Thursday's White House press briefing.

"If we get 75% to 80% vaccinated, we could have a degree of herd immunity to get us back to normal," Fauci added. "The concern I have is people who have vaccine hesitancy who don't want to get vaccinated. We need to do a lot of good outreach."

Fauci said he believes Biden’s goal of 100 million vaccinations in his first 100 days as president "is quite a reasonable goal."

New COVID-19 cases in the U.S. are seeing a "very encouraging" drop, according to The COVID Tracking Project.

The number of weekly cases decreased 21% as of Saturday, the tracker said. There were "more modest but very welcome" drops in COVID-19 deaths and hospitalizations as well.

The seven-day average for cases is back to "pre-Thanksgiving levels," though the group noted there are still nearly three times as many new cases daily compared to the summer peak.