WASHINGTON, D.C. — Anthony Fauci, the nation’s top infectious disease specialist, told a House panel Friday that he is “cautiously optimistic” that a COVID-19 vaccine would be ready by the end of this year and said health agencies are not compromising safety standards.

“I know to some people this seems like it is so fast that there might be compromising of safety and scientific integrity,” Fauci said at a hearing by the Select Subcommittee on the Coronavirus Crisis. “I can tell you that is absolutely not the case.”

Fauci said a vaccine may not immediately be available to everyone once it’s available, but that “over a period of time in 2021” the public would be able to access a vaccine, assuming one is authorized.

Both Oversight and Reform Chairwoman Carolyn B. Maloney of New York and Republican Rep. Jackie Walorski of Indiana pressed Fauci on the likelihood that a vaccine would become available soon and whether Americans should be concerned it would not face rigorous testing.

“I’m so disappointed that we’ve seen some on the other side of the aisle speculate aloud that the administration might rush an unsafe vaccine to the market before the election to help President Trump politically,” Walorski said.

Fauci said any decisions on a vaccine would be based on science.

“The commissioner of FDA has assured me and has spoken publicly that he would make sure any decision on the part of the FDA will be based on sound, scientific data proving the safety and the efficacy,” Fauci told Walorski.

Fauci’s comments come as two vaccine candidates began phase 3 clinical trials this week and a new poll shows public support for carefully testing a vaccine.

A Politico-Morning Consult poll released this week found that 22% of people thought that the government should make a vaccine available as soon as possible, even if it had not been fully tested. But 64% said the government should prioritize fully testing for safety and efficacy even if that means delaying making the vaccine available to the public.

Food and Drug Administration Commissioner Stephen Hahn on Thursday left open a path for using an emergency use authorization for a vaccine before it is fully approved. He said clinical trial data would have to show the same 50% efficacy that the agency has outlined as a goal for a vaccine regardless of whether an emergency use authorization or approval is granted.

“If they met the criteria for safety and effectiveness, we would consider using an emergency use authorization,” he said.