Washington, July 16 : The numbers of Covid-19 cases are surging in more than half of US states and territories, with 7-day average of daily new cases up over 65 per cent from the week before, according to the US Centers for Disease Control and Prevention (CDC). A total of 31,815 new cases were reported across the United States on Tuesday, highest single-day increase since mid May, latest CDC data show, Xinhua news agency reported. The 7-day average of daily new cases is 24,141, up 65.9 percent from the week before. Cases related to the highly transmissible Delta and other variants are rising in the United States. The CDC said it is working with its partners to analyze COVID-19 testing specimens to better understand different variants. Delta, which was first found in India and is now in over 100 countries, represented over 50 percent of new infections in the United States over the two weeks ending on July 3, according to the CDC. Delta is now the dominant strain in the United States, drawing concerns from experts that the variant will cause a surge in new cases this fall. The pace of vaccinations has dropped in the country sharply in the past few months. About 48.2 percent of the US population is fully vaccinated against COVID-19, and 55.7 percent of the population has received at least one shot as of Wednesday, CDC data show. Inequality in access to the vaccine and a racial gap have impacted the success of the nation's vaccination campaign. Federal figures show that counties with higher percentages of black residents have lower vaccination rates in the country. Non-Hispanic Black and Hispanic persons experience higher COVID-19-associated morbidity and mortality, yet COVID-19 vaccination coverage is lower in these groups, according to a CDC study released on Thursday. Coverage and efforts to improve equity in vaccination coverage are critical, especially among populations disproportionately affected by COVID-19, said the CDC. Experts have said COVID-19 vaccines are key to managing spread and prevent variants from mutating into even more dangerous forms. /IANS