The Johnson & Johnson COVID-19 vaccine could be in Tennessee this week. Here's what you need to know.

FILE- This Dec. 2, 2020 photo provided by Johnson & Johnson shows vials of the COVID-19 vaccine in the United States. (Johnson & Johnson via AP)

A third COVID-19 vaccine option and the first to come in a single dose in the United States could be on the ground in Tennessee as early as Monday, according to the state's top health official.

Late Friday, an FDA advisory committee voted unanimously to recommend the Johnson & Johnson COVID-19 vaccine for use in adults 18 and older, and it received formal authorization late Saturday.

Experts say a third vaccine, particularly one that doesn't require ultra-cold storage and that can be completed in one dose instead of two, will be a game changer when it comes to getting more vaccines into arms - a task made even more urgent in the face of rapidly spreading new variants.

"A single shot can have an enormous impact on a pandemic, because there's just a lot of people who - for one reason or another - have difficulty coming back for a second dose," said Deborah Fuller, a professor in the department of microbiology at the University of Washington School of Medicine.

But with so much attention focused on Pfizer and Moderna, which have been the only companies with COVID-19 vaccines available in the U.S. so far, public awareness around the third vaccine has lagged.

Hamilton County Health Department administrator Becky Barnes and interim health officer Dr. Fernando Urrego said in a joint statement via email that they hope people take whatever vaccine option they can get as soon as possible.

"Some may prefer to get the other available vaccines because of the impression that this one is less effective. The reality is that [Johnson & Johnson's] vaccine is very effective in preventing moderate to severe disease as well as preventing hospitalization and death," Barnes and Urrego said.

Weighing the options

Johnson & Johnson's shot was found to be 66.9% effective at preventing moderate to severe illness after 14 days after, and 66.1% effective after 28 days. For severe or critical COVID-19, the vaccine was 76.6% effective after 14 days and 85.4% effective after 28 days, according to an FDA analysis of a multinational clinical trial with more thanr 40,000 participants.

In Johnson & Johnson's entire clinical trial, no coronavirus-related related deaths occured in the vaccine group and no vaccinated people were hospitalized after 28 days.

"That's a huge benefit in terms of reducing the burden of this disease in our health care system," Fuller said.

Though Pfizer and Moderna each boast about 95% efficacy against preventing COVID-19 symptoms, Fuller said it's difficult to compare those vaccines to Johnson & Johnson, because their clinical trials were set up differently.

Pfizer and Moderna both looked at whether people developed COVID-19 symptoms after receiving their second dose of vaccine. In Pfizer's case, the trial began looking for symptoms seven days after the second dose, and Moderna's trial started checking at 14 days post second dose.

On the other hand, Johnson & Johnson studied whether one dose of vaccine protected against moderate to severe infection after both 14 days and 28 days. J&J defined moderate to severe infection as a positive COVID-19 test combined with at least one symptom.

"It's truly like apples and oranges in terms of what's being compared," Fuller said. "One of the big things to keep in mind is that with Moderna and Pfizer, they got two doses, and that's a huge, huge difference. Two doses of a vaccine is always going to give you a lot better immune response than one shot."

Johnson & Johnson now is studying whether two doses of its vaccine are more effective.

In addition, unlike the Pfizer and Moderna vaccines, Johnson & Johnson's vaccine was still being tested as new coronavirus variants were gaining steam. The impact of variants - particularly in South Africa, where the Johnson & Johnson vaccine was determined to be 64% effective at preventing moderate to severe disease - also could explain why Pfizer and Moderna's efficacy data looks better.

"We've been kind of in a way spoiled by these 95% numbers that the [Moderna and Pfizer] vaccines have, but we have to remember how different really these vaccines are," Fuller said.

Regardless of the country, Johnson & Johnson trial data showed the vaccine was still 85% effective against severe disease and 100% against death.

Side effects, which are a normal part of the immune response to vaccinations, were also milder with the J&J vaccine. The most common side effects were pain at the injection site, fatigue, headache, muscle pain and joint pain.

In general, vaccine side effects are usually more intense after a second dose of vaccine, as is the case with Moderna and Pfizer, and in younger people, who have more robust immune systems.

On rare occasions, severe allergic reactions have occurred after the Pfizer and Moderna vaccines. Those have not been reported with the J&J vaccine.

Decades in the making

The technology used in the Johnson & Johnson vaccine is also different from Pfizer and Moderna, but neither technology is new in the field of vaccine research, Fuller said.

"They seem new to everybody, because they're being licensed for use for the very first time, but both of the technologies have been under study for decades," she said.

The Pfizer and Moderna vaccines are made using messenger RNA, or mRNA. They work by delivering a piece of genetic code to cells and teaching them to recognize the "spike protein" of the coronavirus so the body can build immunity to COVID-19, the disease caused by the coronavirus.

Fuller said the J&J vaccine is similar to the other two vaccines in that it also triggers an immune response by showing the body the spike protein, but it uses a different method in order to get that information into cells.

Johnson & Johnson uses an adenovirus, which is a virus family that causes the common cold, that has been modified to the point that it's harmless in order to transport the genetic code of the coronavirus's spike protein to cells.

"Once it gets inside your cells, the virus goes away," Fuller said. "You're just left with that genetic material inside your cells, and then your cells can read that genetic material, just like they do the RNA vaccines."

Johnson & Johnson used the same technique to make an Ebola vaccine that was authorized by the European Medicines Agency in 2020.

Fuller said the technology used in all three vaccines allows them to be tweaked fairly easily, which is a major advantage over traditional vaccines in the fight against new variants.

Johnson & Johnson in Tennessee

Dr. Lisa Piercey, Tennessee health commissioner, said during a news briefing Friday that the state could get as many as 40,000 doses of Johnson & Johnson vaccine this week, but noted that amount had not been confirmed.

Piercey anticipates shipments to start as a "slow trickle" with much of the supply "back loaded" through June.

Barnes and Urrego said they are not sure how much, if any, involvement the Hamilton County Health Department will have in administering the Johnson & Johnson vaccine.

For now, they do not anticipate receiving shipments of the J&J vaccine, but they said they would welcome a third vaccine option.

"Because the logistics of handing this vaccine are so much easier, we believe initially it will go to smaller community providers," they said.

For people who would prefer a certain brand over another, Piercey said vaccination sites and providers who are offering COVID-19 vaccines should say which product they have available.

"We've got quite a bit of Pfizer and Moderna right now, but if we do decide to offer [Johnson & Johnson] in our own health departments, we will be able to give consumers an informed choice. If we send it out to other providers, they will be telling their folks what they can get there," Piercey said.

Fuller said Johnson & Johnson's vaccine fills an important gap left by the RNA vaccines, which have been slow to roll out due to more complex handling requirements and the two-dose requirement. J&J will be able to immunize much more people at a faster rate, she said.

"In a pandemic situation, we have to think about it like a community - that we together as a community are going to solve this problem," Fuller said. "And the way you do that is get as many people immunized as possible. The more people that have resistance to the infection, the quicker we can get the pandemic under control, and get everybody back to their normal life."

With such high demand and need for vaccinations, Fuller recommended that people take whichever they're offered.

"Because we don't know what's going to happen down the line," she said. "We may end up saying, OK, to really get this pandemic under control, we're going to get everybody to come back for another booster immunization, maybe there's a new variant coming out, etc."

She acknowledged that may be easier said than done.

"I develop and design new vaccines. I always thought that was the hardest part. But I'm learning, too, that it's not that simple," she said. "There's a lot of logistics involved there, but I see how people are adapting and addressing the gaps, and they're learning very quickly."

Contact Elizabeth Fite at or follow her on Twitter @ecfite.