WASHINGTON, Jan. 24 (Xinhua) -- A year into the COVID-19 pandemic, the United States is still fighting a brutal battle against the virus as its total number of infections topped 25 million on Sunday.

U.S. COVID-19 cases rose to 25.1 million with over 491,000 deaths as of Sunday evening, according to a tally by Johns Hopkins University.

It took the country just over a year to hit the grim milestone of 25 million infections. The first U.S. COVID-19 case was reported in the state of Washington last January.

Heath experts have attributed U.S. failure to control the virus to political polarization, a rejection of science and an absence of a national strategy under the Trump administration.

The 25 million mark came as President Joe Biden is introducing new measures to bring the pandemic under control.

During his first week in office, Biden issued a detailed new anti-pandemic strategy, pledged to boost testing, vaccinations, supplies and treatments, and mandated masks on federal lands and in inter-state train, bus and air travel.

Stanley Perlman, professor of microbiology and immunology at the University of Iowa, told Xinhua on Sunday that Biden's plan will help better control the virus.

"I think that they will help. Just having a president who believes in the seriousness of the pandemic will help," said Perlman.

The soaring infections have further increased an urgency for a speedier and more effective vaccination push in the country.

The Trump administration failed to fulfill its target of immunizing 20 million Americans by the end of 2020.

Biden's national vaccination campaign aims to administer 100 million doses of two-stage coronavirus vaccines in his first 100 days.

"I think that 100 million doses is feasible, but requires increases in manufacturing and more importantly, more aid to local and state governments to enable effective vaccine distribution," said Perlman.

Dr. Anthony Fauci, the country's top infectious disease expert, said Sunday that Biden's target of 100 million doses in 100 days is not a final number.

"It is really a floor and not a ceiling," Fauci told CBS' "Face The Nation." "It is going to be a challenge. I think it was a reasonable goal that was set. We always want to do better than the goal that you've set."

However, a new model by scientists at Columbia University shows that "vaccines alone are not enough," said a report by New York Times on Sunday.

"The coronavirus pandemic in the United States has raged almost uncontrollably for so long that even if millions of people are vaccinated, millions more will still be infected and become ill unless people continue to wear masks and maintain social distancing measures until midsummer or later," said the report titled "Why Vaccines Alone Will Not End the Pandemic."

Moreover, the spread of a more infectious variant of the virus in the United States could make matters worse.

The new variant, first identified in Britain, has been detected in at least 22 U.S. states, according to data posted Friday by the Centers for Disease Control and Prevention.

A model developed by the Institute for Health Metrics and Evaluation at the University of Washington shows that the United States is projected to see more than 566,000 COVID-19-related deaths by May 1.

Taking into account multiple scenarios based on masking mandates, vaccine distribution and other behavioral changes, the model predicts that deaths in the country will not start leveling off until early March.