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(WHTM) — With the approval of Johnson & Johnson’s COVID-19 vaccine, three different coronavirus vaccinations will soon be available in the U.S. While the Pfizer and Moderna shots have much in common, the new Johnson & Johnson vaccine has some notable differences.

In a Twitter poll, WHTM asked which of the available vaccines people would prefer to get if given the chance to choose:

“All of the vaccines that are available are safe, and they’re very effective,” said Joseph Kontra, chief of infectious diseases at Penn Medicine Lancaster General Health.

They all are doing the same job of mitigating the harms of COVID-19, but the way they do that job differs between vaccines.

How they work

The Pfizer and Moderna vaccines use mRNA technology to build immunity to the novel coronavirus. In contrast, the Johnson & Johnson shot is a type of viral vector vaccine, Kontra explained.

“It’s kind of a Trojan horse mechanism,” says Kontra. Johnson & Johnson’s vaccine involves the insertion of a piece of COVID-19 genetic material into the shell of an adenovirus or a cold virus. Kontra notes that this adenovirus is just a shell, so it cannot replicate or cause an infection.

The immune system takes up this deceptive adenovirus, and then the genetic material inside it starts producing the spike protein that covers the surface of the COVID-19 virus. This prepares the immune system to recognize the COVID-19 spike protein and ward off the coronavirus if an individual becomes infected with the real disease, Kontra said.

Unlike the two-shot Pfizer and Moderna vaccines, only one dose of the Johnson & Johnson vaccine is necessary for it to effectively combat the coronavirus. Researchers are currently studying whether a second dose could make it more effective in the future, Kontra said.


The Pfizer and Moderna coronavirus vaccines are about 95% effective at preventing COVID-19 after both doses have been received. The vaccine made by Johnson & Johnson is 66% effective overall at preventing moderate and severe disease, but it’s 85% efficacious at preventing severe disease, says Kontra.

And, he says, the initial trial of the Johnson & Johnson vaccine showed that it was 100% effective at preventing hospitalization and death from the coronavirus four weeks after the shot had been administered.

Although the Johnson & Johnson vaccine’s 66% or 85% efficacy may sound worse than that of the Pfizer and Moderna inoculations, Kontra says the comparison isn’t really apples to apples.

One reason for this, he said, is that the vaccines “were studied at very different times during the pandemic.” The COVID-19 variants circulating today weren’t around when the Moderna and Pfizer vaccines were being tested.

Another reason is that the parameters of the vaccines’ studies were not identical, he noted.

Kontra said that all three vaccines appear to do what they’re intended to, which is prevent severe complications, hospitalization and death due to the coronavirus.

“I encourage people not to quibble about the efficacy … because the bottom line is all the vaccines are effective and will protect you against COVID-19,” he said.

Dealing with variants

The UK variant of COVID-19 is now present in almost every state in the U.S. and is expected to become the dominant strain of the virus in upcoming months, Kontra said. All three vaccines are effective against this variant, he noted.

Although there is currently no variant that is completely resistant to the vaccines, the three vaccines are less effective against the Brazilian and South African strains, which are currently less common in the U.S., Kontra added.

Variants of the coronavirus are constantly adapting to their environments and evolving to become better at infecting people and spreading. When they have more opportunity to replicate, the likelihood of them developing resistance to the vaccine increases.

“That’s part of the importance of getting people vaccinated as quickly as possible,” said Kontra.

Side effects

The side effects of the Johnson & Johnson shot are similar to those felt after the first dose of the Pfizer and Moderna vaccines, said Kontra. They could include soreness around the injection site, fatigue or body aches.

The more intense side effects associated with the second doses of the Pfizer and Moderna vaccines are not a concern with the single-dose Johnson & Johnson vaccine since the new vaccine only requires one shot.


The new Johnson & Johnson vaccine may play an important role in vaccinating rural and underserved areas.

One reason for this is that storing the Johnson & Johnson vaccine is easier than storing the Pfizer and Moderna shots, which helps simplify distribution, Kontra explained. While the finicky Pfizer vaccine needs to be kept at extremely cold temperatures, Johnson & Johnson’s vaccine is stable in a standard refrigerator.

“So the transport out to rural areas, for example, would be much simpler. And if you’re only giving one shot, you don’t have to worry about bringing everybody back; you can go out to underserved areas and really get the vaccine out to more people,” said Kontra.

The challenge with distributing the new vaccine is that there just isn’t very much of it yet. Kontra said there are fewer doses of the Johnson & Johnson vaccine available now than there were of the Pfizer or Moderna vaccines when they were first approved.

According to a release on the company’s website, Johnson & Johnson plans to have 20 million doses of its vaccine available by the end of March, and it plans to deliver 100 million shots around the U.S. in the first half of 2021.