(AP) Dr. Anthony Fauci says by the end of this year government scientists should know whether they have a safe and effective vaccine for COVID-19.

Fauci is among top officials testifying before the Senate Health, Education, Labor and Pensions committee on Wednesday.

As the government’s leading infectious disease expert, Fauci has been a realist about the dangers of the coronavirus but also optimistic about the prospects for a vaccine. Fauci says people who recover from the virus develop antibodies against it, which gives him confidence a vaccine that triggers the immune system will work.

Fauci says several kinds of vaccines are in final-stage testing in the U.S. A single-dose candidate is the most recent trial, which requires thousands of volunteers.