Texas health care workers, unspecified “essential workers,” Texans who are 65 and older and those who are at increased risk of illness because of underlying medical conditions will have first access to a coronavirus vaccine once it becomes available, according to guidelines published Wednesday by the Texas Department of State Health Services.

And in a signal of optimism about a forthcoming vaccine, Gov. Greg Abbott on Wednesday asked doctors, nurses and pharmacists to sign up for a state program to eventually receive shipments of a vaccine to administer to patients.

State officials predict there will be shortages of vaccine doses and distribution equipment in the initial months after federal regulators approve vaccines for widespread use, which could happen before the end of the year.

"While potential COVID-19 vaccines continue to undergo clinical trials, the State of Texas is taking a proactive approach to ensure the vaccine is distributed as quickly as possible once available," Abbott said in a press release.

And with recent opinion polls showing many Americans are hesitant about taking a coronavirus vaccine, Abbott stressed it would be a “voluntary vaccine” for “Texans who choose to be immunized.”

To sign up to be eligible to receive doses of the vaccine to administer to patients, health care providers must enroll in the state’s immunization registry known as ImmTrac2, identify “critical population groups” they serve and agree to report data to the state about vaccine doses they administer.

Health care workers must also agree to administer the vaccine to patients regardless of their ability to pay.

The state guidelines, which may be updated as vaccines receive regulatory approval from the U.S. Food and Drug Administration, do not offer specifics about what jobs or medical conditions would make a Texan eligible to receive a vaccine in the first phase of distribution along with health care workers and other high-risk people.

But the guidelines include populations deemed “critical,” including:

• Residents of nursing home, assisted living centers or independent living facilities
• Higher education students
• Teachers and professors
• People from “racial and ethnic minority groups” or tribal communities
• Incarcerated people in jails and prisons
• People who live or work in “other congregate settings”
• Rural Texans
• People experiencing homelessness
• People with disabilities
• Uninsured people

Scientists, including Dr. Anthony Fauci, the U.S. government’s top infectious disease expert, have said that initial doses of a vaccine may be ready for high-priority Americans by year’s end.

But requirements for robust scientific study and regulatory decision-making, coupled with herculean efforts needed to scale up manufacturing and distribution of millions of possible doses, likely mean that a vaccine will not be widely available until the second half of 2021, experts have said.

In a letter to health care workers, Texas DSHS Commissioner Dr. John Hellerstedt laid out a rough timeline for vaccine distribution.

In November and December, state officials will identify doctors, nurses, pharmacists and possibly some employers who work with “targeted and prioritized populations” to receive the vaccine once one is approved. Assuming a vaccine is available by then, Hellerstedt said health care workers will likely be able to place regular, additional orders for more vaccine doses in January.

“During this phase, vaccines may still be limited to prioritized populations; however, the larger volumes of vaccines available should reduce the need for highly targeted allocations,” he wrote.

The initial vaccine will be for adults, state health officials said. They offered no timeline for a vaccine approved for use in children but promised to release more information “once the COVID-19 vaccine is approved for pediatric use.”

The governor’s announcement follows new FDA guidelines published Tuesday for pharmaceutical companies seeking the U.S. government’s emergency authorization to distribute a vaccine.

Four vaccines in the U.S. have reached the final stage of large-scale testing in human volunteers, known as a Phase 3 trial. And the New York Times reported Wednesday that a fifth vaccine candidate is expected to start a Phase 3 trial this month. Many clinical trials are recruiting volunteers in Texas.

The new FDA recommendations call for pharmaceutical companies to gather and share comprehensive safety data in the final stage of clinical trials before U.S. officials grant an emergency authorization. Vaccine researchers have said it is possible that some vaccine doses will receive emergency approval by the end of the year, but that approval is extremely unlikely to come before Election Day on Nov. 3, as President Donald Trump has suggested.

There are a number of logistical challenges. Some vaccines under development must be stored at extremely cold temperatures, as low as around minus 112 degrees Fahrenheit. By comparison, most kitchen freezers are about 0 degrees Fahrenheit.

State health officials said the program will not pay vaccine providers to buy freezers, but the Texas Department of State Health Services does not recommend providers purchase a separate ultra-cold storage unit “until further guidance is provided by the CDC.” But they are asking health care providers to submit information about their ability to store vaccine doses at cold temperatures when providers enroll in the vaccine program.

And some vaccines will likely require multiple doses, requiring health care providers to keep track of patients to ensure they receive subsequent injections as appropriate.

Vaccine shipments to health care providers will include needles, syringes, surgical masks and other supplies to help administer vaccines, state health officials said. The federal government has said it will pay for the vaccine shipments and has hired the Irving-based pharmaceutical distribution company McKesson to handle distribution logistics.

The FDA has said for months that it seeks to accelerate the development of vaccines without sacrificing safety. The new guidelines reiterated that idea, saying that an eventual emergency authorization “requires a determination that the known and potential benefits of the vaccine outweigh the known and potential risks.”

The agency asked pharmaceutical researchers to follow clinical trial participants for a median of two months after receiving the final dose of vaccine product. Trials must also have gone on long enough for researchers to document at least five cases of severe infection in participants who received a placebo instead of the vaccine, according to the guidelines. Researchers need to see that at least some people who did not receive the vaccine product became severely ill from COVID-19 in order to assess the risk-benefit calculation of a new vaccine.

In Texas, some large-scale clinical trials have been enrolling participants since July.

A September Axios-Ipsos poll found that six in 10 Americans say they would not take a COVID-19 vaccine as soon as it is available. Poll analysts said the hesitancy reflected a combination of scientists urging patience and the “political pingpong” of President Donald Trump’s insistence that a vaccine will be available before November and Democrats’ pushback against that promise.