Washington, June 30 : The Covid-19 vaccination in the US is slowing down while the highly transmissible Delta variant has spread to nearly every state, fueling experts' fear about potential Covid-19 spikes. The 7-day average number of administered Covid-19 vaccine doses per day has decreased by 55.3 per cent from the previous week, according the latest weekly report of the US Centers for Disease Control and Prevention (CDC). About 46.4 per cent of the US population is fully vaccinated against Covid-19, and 54.2 per cent of the population has received at least one shot as of Tuesday, the Xinhua news agency reported. Roughly 154.2 million people are fully vaccinated. But some states -- such as Alabama, Arkansas, Louisiana, Mississippi, Tennessee and Wyoming -- have low vaccination rates. The White House has confirmed the country will not hit US President Joe Biden's goal of getting 70 per cent of American adults to receive at least one Covid-19 vaccine shot by the Fourth of July. Amid the slowdown of vaccination rates, the infections caused by variants, especially the highly contagious Delta variant which was first recognised in India, are climbing. The proportion of the Delta variant infections for the 2-week period ending June 19 is expected to increase to 20.6 per cent nationally and be higher in some regions, according to the CDC. The figure was only 2.8 per cent in the 2-week frame ending in May 22, and increased to 9.5 per cent in the 2-week frame ending in June 5, CDC data show. The infections caused by the Delta variant now account for one fifth of the newly diagnosed Covid-19 cases in the US, according to the CDC. The variant is expected to become the dominant coronavirus strain in the US, CDC Director Rochelle Walensky warned. In Los Angeles County, the pace of Delta's spread has prompted officials to reinstate mask guidance for public indoor spaces -- regardless of vaccination status. The new, voluntary mask guidance is needed until health officials can "better understand how and to who the Delta variant is spreading," the county's department of public health said. Experts are concerned the variants could cause a resurgence of Covid-19 in the fall if the unvaccinated population do not take actions in a timely manner. The mRNA Covid-19 vaccines, which are made by Pfizer/BioNTech and Moderna, appear to hold up against the Delta variant, according to White House chief medical advisor Anthony Fauci. The Pfizer/BioNTech vaccine was 88 per cent effective in preventing Covid-19 symptoms in the Delta variant two weeks after the second dose of the vaccine, he said. US Officials repeatedly urged Americans to get vaccinated as soon as possible. /IANS