The Centers for Disease Control and Prevention released data Monday tracking the progress made by states to administer COVID-19 vaccine.So far, about 15.4 million doses have shipped throughout the country. That’s just shy of the 20 million doses U.S. officials had promised to distribute by the end of 2020. However, health experts are more concerned with the lag in COVID-19 vaccinations. Only about 4.5 million people have received their first dose as of Tuesday, the CDC reports. That means just 30% of available doses have been used.Officials say the pace of vaccinations should be picking up in the upcoming weeks, but a host of logistical challenges and differing approaches stand in the way. Operation Warp Speed’s Gen. Gustave Perna also said in a briefing last Wednesday that the holidays may have played a part in the delay.Currently, about 200,000 doses are being given a day. Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said vaccinators should soon be able to deliver 1 million a day.While some states have been more successful overcoming the obstacles to vaccinate their residents with available doses, other states seem to be falling behind.These states have vaccinated the fewest residents with their available doses:Kansas: 131,750 distributed; 20,110 administered (15.26%) Georgia: 483,650 distributed; 75,157 administered (15.54%) Arizona: 411,025 distributed; 66,059 administered (16.07%) Louisiana: 218,425 distributed; 49,589 administered (22.70%) Virginia: 468,950 distributed; 108,861 administered (23.21%) Kansas officials have blamed lags in reporting for the apparently slow movement of vaccines from the warehouse to patients’ arms. State officials said they are pushing shipments out to vaccinators statewide rather than targeting a few urban hospitals, and they said the decision be making centralized data collection more complicated.Based on the CDC’s latest data, these states have vaccinated the most people with their available doses:South Dakota: 43,325 distributed; 26,913 administered (62.12%)North Dakota: 37,900 distributed; 22,240 administered (58.68%) Tennessee: 300,250 distributed; 152,516 administered (50.80%) Connecticut: 149.900 distributed; 75,946 administered (50.66%) Maine: 66,250 distributed; 31,663 administered (47.79%) Contributing: Mike Stucka, Karen Weintraub, USA TODAY. Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT. Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.