The Trump administration’s top health official on Wednesday dismissed concerns over the potential for a “vaccine cliff” once initial supplies of the Pfizer and Moderna COVID-19 vaccines are exhausted.

Health and Human Services Secretary Alex Azar said the administration is confident that it has enough contracts with other companies to make sure there are enough doses of a vaccine for all Americans.

“We are very confident that during the second quarter of next year we’ll have enough vaccines for every American who wants to be vaccinated,” Azar said during the Milken Institute’s health summit. “So, I don’t see where this math is coming from.”

The administration’s goal is to vaccinate 20 million by the end of the year. Azar said the goal for the end of January is to inject at least 50 million people with the first of two doses.

The administration’s Operation Warp Speed currently has contracts for 100 million doses of the COVID-19 vaccine from Pfizer and BioNTech, as well as 100 million doses of a vaccine from Moderna.  

But the U.S. declined to purchase additional doses of the Pfizer vaccine when offered, and the companies’ international commitments mean the U.S. won’t be able to easily acquire more doses if they are needed. 

Operation Warp Speed has contracts with a total of six different companies for at least 800 million doses, including the 200 million from Pfizer and Moderna, with the option for up to 3 billion doses. 

The other companies include Johnson & Johnson and AstraZeneca, both of which have vaccines that are still in late-stage trials. 

Warp Speed officials said they expect interim data from Johnson & Johnson’s trial in early January, though company executives have said that because of how quickly the virus is spreading they could have data before the end of the year. Emergency authorization could come by early 2021. 

AstraZeneca released partial data this week, but missteps during the trial process have made regulators skeptical. The company won’t have a complete readout of results until January or early February, and it’s unclear when they might ask for emergency authorization. 

Azar acknowledged the projections were based on the assumption that the other companies would be able to show their drugs are safe and effective and then be able to quickly scale up production. 

“Let’s be really clear, we give projections, based on our best estimate of probability of technical success of different platforms, different vaccines, but also manufacturing timelines,” Azar said. “Protein biologic manufacturing, it’s a finicky process. It’s something that you want to be careful about your projections.”

During a separate call with reporters Wednesday, Warp Speed’s CEO, Gen. Gustave Perna, said the administration understands that vaccine production and distribution doesn’t happen in a vacuum.

“If your plan is based on perfection, I can guarantee you execution will not equal perfection. So you have to put things in place to mitigate where you’re vulnerable,” Perna said.

Still, Azar said the hope is that AstraZeneca and Johnson & Johnson will be safe and effective and will be able to quickly get enough doses shipped to the American people.  

“We keep expanding production each week and then we hope also to add in other manufacturers like AstraZeneca and Johnson & Johnson as we move in perhaps into the February timeframe. So you’re talking about literally many tens of millions of people each month,” Azar said.