Once 75%–80% of people get vaccinated against the coronavirus, there should be strong enough herd immunity that we can return to normal activities, NIAID director Anthony Fauci tells Axios.

Driving the news: The FDA is meeting with outside experts today as the agency considers granting an emergency use authorization to Pfizer-BioNTech for their COVID-19 vaccine. A similar meeting is slated for next week to discuss a vaccine developed by Moderna.

The big picture: Mass vaccination faces a myriad of hurdles that must be overcome — nationwide planning and logistics, vaccine production, public distrust, and lingering scientific unknowns.

"What we have to see is a rate of test positivity that's extremely low. I mean, really low. But the real proof in the pudding is how many people in the United States get vaccinated," Fauci says.

• "If you have 75%–80% of the people get vaccinated, you create an umbrella of herd immunity — that even though there is virus around, it is really almost inconsequential because it has no place to go, because almost all of the people are protected," Fauci says.

But several hurdles have to be addressed, several public health experts say.

1. Sustain current public health measures, like mask wearing and social distancing, while the vaccines are rolled out and distributed.

• "You can't give them up completely until you get such a level of herd immunity that the virus has no place to go," Fauci warns.

2. Determine logistics and an equitable distribution of vaccines. Several of the vaccines have strict cold-chain requirements that require planning, and there's concern the most vulnerable may not get access quickly.

• The biggest challenge is how "to get the vaccine to the American public state by state, county by county, block by block, arm by arm, in a country as large and diverse as ours," Michael Fraser, of the Association of State and Territorial Health Officials, told a Johns Hopkins Center for Health Security webinar Wednesday. He added it will depend on individual mayors and state/county officials.
• Fraser said the U.S. needs a unified concept of operations so Americans understand how they can obtain a vaccine in their state plus a scale-up of the public health workforce.

3. Address misinformation. "We need strong scientific communicators" to explain the terminology and what people should expect, Julie Fischer, senior technical adviser for global health at CRDF Global, tells Axios.

• Polls vary on the number of Americans who say they plan to get vaccinated, but it appears around one-third say they will not get one. Many don't trust social media information on the vaccines, but their trust in personal doctors tends to remain high — and health officials hope this will be one route to combat misinformation.
• "We are working closely with physician groups, provider groups, to make sure all of their questions are answered, so that they can address their [patients'] hesitancy and get behind this important resource for the public's questions," Ngozi Ezike, director of the Illinois Department of Public Health, said at the webinar. "As health care providers, we are the motivators-in-chief."

4. Explain the science behind vaccines, particularly mRNA ones. "Even though this is a new technology, it's actually a huge improvement on the old, crude ways of making vaccines," Fischer says.

• But public health officials need to better explain how mRNA vaccines briefly teach the body to produce an immune response to SARS-CoV-2 and then the body breaks down and eliminates the RNA, and does this without affecting the person's DNA, she says.
• Plus, every doctor and researcher has been "actively searching for adverse effects" that would contraindicate offering the vaccine to healthy people, which they have not found, Fischer adds.

5. Continue gathering scientific data about remaining scientific unknowns in a transparent way.

• While the vaccines appear to prevent severe illness, it remains unknown if a vaccinated person might still be able to transmit the disease, Fischer says. As data is collected, we should be able to determine if they provide "sterilizing immunity" that prevents infection or "effective or practice immunity," which means a person is protected against severe disease but could still be a carrier.
• "We know reinfection occurs, because there are documented cases. What we don't know is the extent of it," Fauci tells Axios. Close to 14 million people in the U.S. have been infected, so Fauci says he'd expect to see a lot more reinfection if it was happening.

The bottom line: "For everyone who has been struggling with the real uncertainty of when this all ends and we can go back to the beforetimes, we have an actual light at the end of what has seemed to be a very, very long tunnel," Fischer says.