Last week, the director of the Centers for Disease Control and Prevention (CDC) told governors to be prepared for the “large-scale” distribution of a coronavirus vaccine by Nov. 1, according to a letter obtained by NBC News.

In the letter dated August 27, CDC director Dr. Robert Redfield said the agency had contracted with a pharma company, McKesson Corp., to distribute hundreds of millions of coronavirus vaccine doses to medical facilities and health departments across the nation in the fall.

Dr. Redfield called the effort “massive” and asked states for their help expediting applications for distribution facilities, which will be set up and operated by McKesson.

The CDC director added, “If necessary, the agency asks you to consider waiving requirements that would prevent these facilities from being fully operational by November 1, 2020.”

However, it is still uncertain whether a vaccine will be ready by then or which manufacturer will make it.

The November 1 target date is just two days before the presidential election.

Banner Health, which operates 28 hospitals in Arizona, said it had been asked by the CDC and local health authorities to “proactively prepare” for vaccine distribution.

It said, “While we do not yet know definitively when a vaccine will be available, pre-planning will ensure we can effectively meet the needs of our communities.”

FDA Commissioner Dr. Stephen Hahn told The Financial Times that the federal agency could fast track a vaccine.

He said, “We may find that appropriate. We may find that inappropriate. We will make a determination.” It was not clear which company will get the approval.

Two vaccine candidates — one led by Moderna and the National Institutes of Health (NIH) and another led Pfizer and BioNTech — began Phase 3 clinical trials this summer.

Another company, AstraZeneca, is working on its vaccine candidate, which has begun its Phase 3 trials this week.

On Wednesday, Dr. Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases (NIAID) said on NBC’s “TODAY” that he believed a COVID-19 vaccine would be developed by the end of the year.

However, Dr. Fauci added that he would not be comfortable with a vaccine unless its clinical trials show it “to be clearly safe and effective.”

The NIAID director went on to say a potential coronavirus vaccine could be available if the trials produce overwhelmingly positive results. Dr. Fauci said he had observed many clinical trials that are operated under the FDA’s Emergency Use Authorization method. He said, “But they’ve been done when there was enough data that you would really feel comfortable that it was safe.”