The FDA Just Authorized Johnson & Johnson’s Single-Shot Vaccine for Emergency Use—Here’s How it Stacks Up

As the Pfizer and Moderna COVID-19 vaccines continued to be given around the US (and the world at large), a third looks set to be authorized by the Food & Drug Administration (FDA). The Johnson & Johnson vaccine was developed by Janssen Pharmaceutical Companies—a Belgium-based division of the company—in collaboration with Beth Israel Deaconess Medical Center. It has "known benefits" in reducing both symptomatic and severe illness, according to a briefing document published February 26 by the FDA.

In clinical trials, the Johnson & Johnson vaccine was more than 85% effective in preventing serious illness and offered complete protection against COVID-19 hospitalization and death. It had an overall effectiveness rate of 66% when moderate cases were taken into account at least 28 days post-vaccination. In the US specifically, researchers shared that the vaccine was 72% effective in preventing moderate to severe COVID-19.

Crucially, the Johnson & Johnson vaccine shows signs of working against the more transmissible 501.V2 variant now prevalent in South Africa. Trials there showed the shot to be 82% effective in preventing severe or critical illness and 64% effective in stopping moderate to severe illness.

So how does it work, and how is it different from the Pfizer and Moderna vaccines? Here's what you need to know.

How does Johnson & Johnson’s COVID-19 vaccine work?

Like the Pfizer and Moderna vaccines, the new vaccine is based on the virus's genetic instructions for building the spike protein. But while the Pfizer and Moderna vaccines store the instructions in single-stranded RNA, the Johnson & Johnson vaccine uses double-stranded DNA.

It's what's known as a viral vector vaccine, which uses a modified version of a different virus (a vector) to deliver instructions, in the form of genetic material (a gene), to a cell. In this case, Johnson & Johnson used a harmless adenovirus (a common virus that typically causes cold or flu-like symptoms) as the viral vector—known as Ad26—replacing a small piece of its genetic instructions with coronavirus genes for the SARS-CoV-2 spike protein.

The adenovirus was modified, so it can enter cells but can't replicate inside them or cause illness. When this modified adenovirus is injected via vaccine, it enters the person's cells— they then read the genetic instructions needed to make the spike protein and the vaccinated cells make and present the spike protein on their own surface. The person's immune system recognizes these foreign proteins and makes antibodies against them that will protect the person if they are ever exposed to SARS-CoV-2 in the future.

Other coronavirus vaccines based on adenoviruses include the one developed by the University of Oxford and AstraZeneca, which uses a chimpanzee adenovirus.

Another important difference between the Johnson & Johnson vaccine and the Pfizer and Moderna vaccines is that it is a single-shot vaccine (both Pfizer and Moderna require two shots for complete protection, spaced 21 and 28 days apart, respectively). Since Johnson & Johnson's vaccine requires fewer doses, it will also require fewer vaccine appointments and medical staff, making it a far more cost-effective option.

What are the side effects of Johnson & Johnson’s vaccine?

Up front, the FDA said none of the side effects reported by participants in the Johnson & Johnson trials would prevent them from authorizing it. According to the briefing document published by the FDA, the vaccine's most frequently reported adverse reactions were pain at the point of the injection, headaches, and fatigue—the same as have been reported with the Moderna and Pfizer vaccines.

Additionally, according to reporting by STAT News covering the FDA's Friday meeting to decide the fate of the Johnson & Johnson vaccine, scientists pointed out three conditions that may have been linked to the COVID-19 vaccine in some patients: clotting disorders, tinnitus (aka, buzzing or ringing in the ears), and urticaria or hives. The FDA also shared that three serious adverse events occurred, likely linked to the receipt of the vaccine, though all three people recovered. No deaths were reported among participants who had received the Johnson & Johnson vaccine, and there were no hospital admissions after 28 days post-vaccination.

What are the ingredients of Johnson & Johnson’s vaccine—and how is it stored?

According to the FDA briefing document, the ingredients in Johnson & Johnson's COVID-19 vaccine are as follows:

• Ad26 vector expressing SARS-CoV-2 spike protein
• Citric acid monohydrate
• Trisodiumcitrate dihydrate
• Ethanol
• 2-hydroxypropyl-β-cyclodextrin (HBCD)
• Polysorbate 80
• Sodium chloride
• Sodium hydroxide
• Hydrochloric acid

As for how it's stored, adenovirus-based vaccines for COVID-19, like Johnson & Johnson's, are more robust than the mRNA vaccines from Pfizer and Moderna (DNA isn't as delicate as RNA in the first place, and the adenovirus has a hard, protective protein coat). That means Johnson & Johnson's vaccine can be stored in a refrigerator instead of a freezer like the other two vaccine options. The "fridge stable" vaccine can be refrigerated for up to three months at 36–46°F (2–8°C), making it easier to ship and distribute.

So, what happens now with Johnson & Johnson’s vaccine?

Prior to the FDA's emergency use authorization, at least three million doses of the Johnson & Johnson vaccine will be distributed next week, said a White House official, per Reuters.

Thereafter, at least 20 million doses will be delivered by late March, and 100 million in total by the end of June. The UK, EU, and Canada have also got orders in, and 500 million doses will be supplied to more than 180 poorer nations through the Covax scheme, which was launched in April 2020 by the World Health Organization (WHO), together with the Global Vaccine Alliance and the Coalition for Epidemic Preparedness Innovations.

The new Johnson & Johnson vaccine will now join the others in the fight against COVID-19. In the US, more than 65 million people have already been vaccinated, with around 1.3 million doses being administered across the country every day.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.

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