Although more and more contagious variants are spreading in the US, the leading health authorities expressed optimism on Sunday that both the supply of vaccines and the vaccination rate will steadily increase.

“The demand currently significantly exceeds the supply,” said Dr. Anthony S. Fauci, the nation’s leading infectious disease doctor, on NBC’s Meet the Press program.

“I can tell you that things will get better from February through March through April because the number of vaccine doses available will increase significantly.”

The number of daily shots administered in the United States has increased recently. The Centers for Disease Control and Prevention reported that more than 2.2 million doses were given on Saturday and 1.6 million on Friday. The average for the past seven days has been 1.4 million a day, which is close to President Biden’s new target of 1.5 million shots a day.

In addition, the supply of vaccines is growing – although still well below demand. Federal officials recently increased shipments to the states to 10.5 million cans per week as Moderna and Pfizer incrementally increase production. The two companies have signed deals to provide the US with a total of 400 million doses by the summer – enough to vaccinate 200 million people.

Pfizer recently announced that it will now dispense its doses two months ahead of schedule by May, also because it now counts an extra dose in each vial it makes. And Moderna is considering a production change that would allow it to increase the number of doses in its vials from 10 to 15.

Officials also expect the Food and Drug Administration to approve a vaccine containing a dose of Johnson & Johnson later this month. Although this company will initially only supply the US with a few million cans, it is expected to increase production significantly by April. Other vaccines from Novavax and AstraZeneca could also be approved for use in the US this spring, further increasing supply.

Officials are trying to vaccinate as many people as possible to beat more contagious variants of the virus first identified in the UK and South Africa. The variant from Great Britain known as B.1.1.7 is spreading rapidly in the USA. According to a new study, their prevalence doubles roughly every 10 days. The CDC said it could become the dominant form of the virus in the United States by March.

While this variant is of concern because it is more transmissible than previous variants, vaccine developers are more concerned about a variant discovered in South Africa, known as B.1.351, as it appears to interfere with current vaccine effectiveness. Several manufacturers said they are addressing the problem by developing new versions of their vaccines that could serve as booster shots. The Food and Drug Administration has announced that it is working on a plan to allow these new versions of the vaccine to be approved.

AstraZeneca and Oxford University developers of the vaccine announced on Sunday that they are expected to have a modified version of their vaccine available in the fall.

Dr. Scott Gottlieb, former FDA commissioner and member of the Pfizer board of directors, said on CBS’s Face the Nation program on Sunday that it was possible to develop a booster that “bakes in many different variations,” we see. “

“I think there is a reasonable chance that we can be one step ahead of this virus,” he said.