Why Johnson & Johnson's COVID-19 vaccine is probably the best shot

• Pfizer's and Moderna's COVID-19 vaccines were near perfect at preventing symptomatic infections in trials.
• Johnson & Johnson's shot has benefits: It's cheap, easy, and mild, and it performs against variants.
• The truth is you can't pick out which vaccine you get anyway, so it's a good thing they all work.

Americans have had two extremely similar authorized COVID-19 vaccines since December: one mRNA vaccine from Pfizer, and another mRNA vaccine from Moderna.

But now, there is another coronavirus shot authorized for use across the US: Johnson & Johnson's adenovirus jab, which got a green light from the US Food and Drug Administration on Saturday after an expert committee unanimously recommended on Friday evening that it should receive emergency-use authorization.

In trials around the world, J&J's shot was shown to be 66% effective at preventing coronavirus infections altogether, and 85% effective at preventing severe COVID-19 cases, when given four weeks to take effect.

Taken at face value, that may not appear as good as Moderna's or Pfizer's two-shot vaccines, both of which had efficacy better than 94% in their 2020 trials.

But don't be fooled by the buffet of incomplete vaccine data we have. Comparing efficacy rates among different vaccine trials conducted at different times is like comparing apples to oranges. That's why Dr. Anthony Fauci and other experts have said they would just take whichever shot they could get.

And for some people, getting the J&J vaccine may be ideal.

Young, healthy people, and those who can't necessarily afford to come back for a second jab, may prefer it, and others who don't tolerate vaccine side effects well might like it better too. Plus, you have to consider that J&J's shot was tested out at the height of the pandemic, which may have had an effect on the numbers in the trial.

While it may not eliminate disease, J&J's jab holds its own in preventing the worst outcomes of COVID-19 - hospitalization and death. What's more, it's cheap to make, simple to give and get, and you'll gain some good viral protection in just a matter of weeks, without ever having to return for a second shot. As a bonus, you just might be better protected than anyone else against some new variants that are spreading fast.

In short, this vaccine could be the pandemic escape hatch we've been waiting for - helping vaccinate millions more Americans at a breakneck clip.

Experts are excited to have a single-dose vaccine

The most obvious benefit of the J&J vaccine is it's just one shot.

"It's nice to have a single-dose vaccine," FDA committee member Eric Rubin, editor in chief of the New England Journal of Medicine, said Friday evening after the vote. "The demand is so large that it clearly has a place."

The rest of the FDA committee agreed.

"What we have to keep in mind is we are still in the midst of this deadly pandemic," committee member Archana Chatterjee, dean of the Chicago Medical School, said. "There is a shortage of vaccines that are currently authorized, and I think authorization of this vaccine will help meet the needs of the moment."

Adding millions more shots to the US's vaccine arsenal will help drive up the collective immunity of the country. And one shot can do that quicker than two. Not only is the J&J vaccine simpler to give out, requiring no second appointments, it's also significantly cheaper to produce than mRNA shots - making it a great tool to fight the pandemic worldwide. (All the authorized COVID-19 vaccines are, under federal law, free to everyone in the US.)

It works particularly well in young people

For younger, healthier people the convenience factor of a one-shot vaccine is not trivial.

People under 60 are generally not at great risk of major COVID-19 complications in the first place, and are more likely to struggle taking time off work, but it's still imperative that they get vaccinated.

They can do their part to combat the pandemic without having to schedule two vaccine appointments (or accidentally skip the second). With J&J's shot, immune protection will become robust within a month, without having to go back in for a second booster.

Fortunately, this new vaccine works particularly well in the under-60 group too. In J&J's trial, people under the age of 60 were well protected from serious infections: Only 58 out of more than 8,200 who were fully vaccinated got moderate to severe illness after their shot had time to take effect. In the similarly sized control group, 180 got moderate to severe COVID-19 infections.

J&J's shot is also the only one that the FDA has reviewed, so far, that provides evidence that it helps stop people from spreading the virus asymptomatically. That is particularly useful for young people, as well as essential workers and people experiencing homelessness who may not be able to social distance, and already face more barriers getting access to vaccine or testing sites.

Though more research is needed to know for sure, J&J's data suggests that their vaccine may be about 74% effective against asymptomatic infections. That means it could be a great tool to help achieve herd immunity nationwide, by stopping the silent, undetected spread of the virus.

It's safe and likely doesn't require a day of rest

Both Pfizer's and Moderna's two-dose mRNA shots come with some more serious side effects than J&J's. Though temporary, the fever, chills, and general malaise people may feel the day after getting their second shot (called the booster) can be severe enough to affect their daily plans.

Lots of people who've had strong reactions to their second shot of Pfizer's or Moderna's vaccine are recommending others take a day off work after shot No. 2, or they schedule their appointment over the weekend. But not everyone can afford to do that.

J&J's vaccine is also more convenient for providers. It is less fragile, so it can sit in a regular fridge for three months, without requiring any of the hypercold storage mRNA vaccines do. This could make it an indispensable tool in rural areas. The vaccine may also be a better choice for some people who have polyethylene glycol allergies.

It's the only vaccine we know that works against variants in the real world

Pfizer and Moderna set a stunningly high bar as the first vaccines with results from late-stage studies.

"We have a vaccine now that has good efficacy that everyone is going to compare to the existing vaccines and say it doesn't look quite as good," Rubin said.

But there's more to J&J's result than that single number.

"What's really important to remember about this vaccine is that when we conducted our clinical trials, in October of 2020 to about January of 2021, this was during the time when the incidence rate of the virus was really about at its peak," J&J CEO Alex Gorsky told NBC's "Today" show on Monday.

J&J's shot is also the only vaccine to have rigorous clinical data showing success in numerous countries where variants of the virus are rapidly spreading. In particular, J&J's shot was 64% effective in South Africa, where virtually all the local illnesses during the study were caused by the B.1.351 variant.

Mathai Mammen, J&J's research and development head, told Insider that the company's shot has been "co-optimized" for both antibody and T-cell responses to the virus, while both Pfizer's and Moderna's have not.

"That makes our vaccine potentially really good versus a virus that is changing on us," he said. "We're worried about the mRNA vaccines not having that T-cell net and actually taking a much bigger hit by the South African variant."

Mutations seen in the B.1.351 variant have concerned vaccine developers to the point that Moderna and Pfizer are now developing new booster shots of their vaccine, tailored to neutralize that concerning variant.

Moderna and Pfizer are confident that their shots will still provide protection, at least partially, against these concerning variants. J&J's shot, in contrast, brings certainty that it is.

"We're in a race between the virus mutating, new variants coming out that can cause further disease, and stopping it," Dr. Jay Portnoy, the FDA committee's consumer representative said. "We need to get this vaccine out."

You might get a little sick

Even though J&J's vaccination may not eliminate disease entirely, it makes getting COVID-19 tolerable.

People who were vaccinated with J&J's shot in the trial but got sick - in what are called "breakthrough" infections - had much milder symptoms.

Dr. James Hildreth, also on the FDA expert advisory committee, said it was an "important point" about the shot.

It's similar to what happens with annual flu shots: They tend to make flu symptoms milder and illnesses shorter, when and if vaccinated people do get infected. That'll be an important feature of any good coronavirus vaccine, as COVID-19 becomes endemic.

Starting four weeks after immunization, no one receiving J&J's vaccine was hospitalized. There were also no deaths among vaccinated participants (seven people who got the useless placebo jab died during the vaccine study in South Africa).

"The efficacy at preventing relatively mild or even moderate disease may be different," Dr. Cody Meissner, an infectious-disease expert at Tufts School of Medicine, said during the FDA meeting on Friday, speaking of the differences between Pfizer, Moderna, and J&J.

"Yet all of the vaccines seem to be equally effective at preventing very severe disease, intensive-care needs, and deaths."

And isn't that what all the best vaccines are designed to do? Keep us alive and free of serious diseases.

As the virologist Angela Rasmussen said Wednesday on Twitter, "I'll take it."

She added: "I'd recommend it to my parents and older relatives too."