On Sunday, President Joe Biden said it is very difficult to achieve herd immunity to the coronavirus in the U.S. by the end of summer, hinting that there could be a long road ahead to defeating the virus.

In an interview broadcast on CBS ahead of the Super Bowl, the 78-year-old said, “The idea that this can be done and we can get to herd immunity much before the end of this summer is very difficult.”

Responding to journalist Norah O’Donnell, Biden said it would take almost a year to vaccine enough people to achieve her immunity at the current rate of about 1.3 million doses administered per day.

The Biden administration has set a goal of 100 million doses in the first 100 days of his presidency, though the pace of vaccinations is currently higher than that.

The president seemed to up his goal late last month. He said he thinks the U.S. could administer up to 1.5 million doses per day, according to CNBC.

Biden’s comments are well within the line of warnings of researchers and public health officials as well as his past statements.

Dr. Anthony Fauci, Director of the National Institute of Allergy and Infectious Diseases (NIAID), said that to achieve herd immunity, it would require a minimum of 75% of Americans to be vaccinated against the virus, predicting a return to normal at least by next fall.

During the interview, Biden also went on to say he was exploring new ways to vaccinate more people as quickly as possible.

He said he supported a proposal from the National Football League (NFL) to use its 30 stadiums as mass vaccination centers; however, stopped short of committing to the plan.

Biden said, “I’m telling my team they are available, and I believe we’ll use them.”

So far, the coronavirus has infected more than 27 million Americans and killed more than 474,000 people. The story was originally published on CNBC.