How Does Johnson & Johnson’s Single-Dose COVID-19 Vaccine Work?

Phase 3 trials just wrapped up, and the early data is very promising, experts say.

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While Pfizer-BioNTech and Moderna both have 95% effective COVID-19 vaccines authorized for emergency use in the U.S., other vaccine candidates are still in the works, including a single-dose option from Johnson & Johnson, which enrolled about 45,000 people in its global phase 3 clinical trial. According to early data released by the company, this vaccine also shows strong promise.

The Johnson & Johnson vaccine is 66% effective overall in preventing moderate to severe forms of COVID-19 28 days after a person is vaccinated, but that number jumps to 72% in the U.S. specifically and to 85% when it comes to preventing severe forms of COVID-19 that can lead to hospitalization and death.

The news may sound a bit disappointing, given the higher efficacy rate of the available vaccines, says Richard Watkins, M.D., an infectious disease physician and professor of internal medicine at the Northeast Ohio Medical University. However, he says it is worth noting that “the flu vaccine is usually up to 60% effective,” and that annual shot plays an integral role in decreasing flu-related hospitalizations and deaths every year.

What’s really important with the vaccines is “not how well it protects against symptomatic disease, but how well it protects against severe disease,” says infectious disease expert Amesh A. Adalja, M.D., senior scholar at the Johns Hopkins Center for Health Security.

Anthony Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases, says the Johnson & Johnson vaccine will still be an important player in reducing the stress on our healthcare system once it receives approval for emergency use from the Food and Drug Administration (FDA). “If you can prevent severe disease in a high percentage of individuals, that will alleviate so much of the stress and human suffering and death,” he said in a call with reporters on Jan. 29.

Johnson & Johnson has also leaned heavily into the fact that its vaccine requires just a single dose compared to the Pfizer and Moderna vaccines, which both require two doses. What’s more, it uses different vaccine technology that’s much easier to store safely. Here’s everything we know so far, plus what lies ahead.

How does the Johnson & Johnson COVID-19 vaccine work?

Johnson & Johnson has an andenovector vaccine, which uses double-stranded DNA to promote an immune response in the body. This technology works differently than the mRNA vaccines available from Pfizer and Moderna, which both use single-stranded RNA.

In the Johnson & Johnson vaccine, researchers added a piece of genetic material from the novel coronavirus’ spike protein (the piece that latches onto human cells) into another virus, Adenovirus 26, which was modified so it has the ability to enter cells but not reproduce inside of them. Adenoviruses are common viruses that usually cause cold-like symptoms, but because the one used in the vaccine was altered and cannot replicate, it can’t make you sick. (Other COVID-19 vaccines, including Oxford and AstraZeneca’s candidate, uses similar adenovirus technology.)

When you get the Johnson & Johnson vaccine, the modified adenovirus carrying a piece of the spike protein latches onto the surface of your cells. It’s pulled inside, where the modified virus travels to the cell nucleus, home to its DNA. The adenovirus then puts its DNA into the nucleus, the spike protein gene is read by the cell, and it’s then copied into messenger RNA (mRNA).

After that, the mRNA leaves the nucleus and serves as a set of instructions for other cells, so they begin making spike proteins. Those are then recognized by your immune system, and your body reacts by producing antibodies to the perceived threat (even though no threat exists).

Your immune system cells then remember how to fight the distinct piece of SARS-CoV-2, the novel coronavirus, so if you come into contact with it in the future, your body will have the capability to fight it more efficiently.

This technology is unique but Johnson & Johnson has a lot of experience with it, as it’s already been used for its Ebola vaccine. “They’ve given hundreds of thousands of doses of this similar vaccine,” which has had no major safety issues, says William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine.

How effective is the Johnson & Johnson COVID-19 vaccine?

Again, the vaccine was found to be 66% effective overall at preventing moderate to severe forms of COVID-19 and up to 85% effective for severe disease in the phase 3 clinical trial. The vaccine also offered “complete protection against COVID-related hospitalization and death” in all study participants 28 days after they were vaccinated, the press release says.

The level of protection differed slightly depending on where it was studied. In the U.S., it was 72%; in Latin America, it was 66%; in South Africa, it was 57%. The reason wasn’t overtly clear, but it is likely due to different variants of the coronavirus circulating in those regions, Dr. Watkins says.

Dr. Adalja is hopeful, because “the clinical trial results look strong.” Dr. Russo agrees that “as of right now, there are no major concerns with the safety signals.”

What are the side effects of the Johnson & Johnson COVID-19 vaccine?

The vaccine was “generally well-tolerated” in study participants, Johnson & Johnson said in a press release. According to the data so far, the vaccine may cause “mild-to-moderate side effects typically associated with vaccinations,” similar to those expected from the Pfizer and Moderna vaccines. This includes cold-like symptoms, like a headache, body aches, pain at the injection site, and a fever—a normal sign that the body’s immune response is being primed.

How is the Johnson & Johnson COVID-19 vaccine stored?

      One of the biggest perks of the Johnson & Johnson vaccine is its durability. Because it doesn’t harbor delicate mRNA like the Pfizer and Moderna vaccines (which need to stay frozen), it’s much less fragile and can stay stable in a normal refrigerator (36–46°F) for up to three months.

      “That’s a big advantage,” says Thomas Russo, M.D., professor and chief of infectious disease at the University at Buffalo in New York. Safely storing the other available vaccines, particularly the Pfizer vaccine (which needs to be kept at a frigid -94°F), presents challenges for the average doctor’s office or pharmacy, as most locations don’t have specialty freezers that reach those temperatures.

      When will it be granted an emergency use authorization by the FDA?

      Now that its phase 3 clinical trial has wrapped up, Johnson & Johnson can apply for emergency use authorization from the FDA. Dr. Russo estimates that the vaccine could be authorized sometime in March.

      In August, the company signed a $1 billion contract with the federal government, pledging to produce 12 million doses of its vaccine by February and 100 million doses by the end of June. However, The New York Times reports production may be about two months behind schedule.

      Will you get to choose which COVID-19 vaccine you get?

      At this point, that doesn’t seem likely. “In this initial phase of vaccinations, there’s probably not going to be much of a choice for people,” Dr. Adalja says. Rather, the health department or agency administering the vaccine will make the decision, mostly based on which vaccine is readily available in a specific area. However, once one becomes available to you, it’s crucial to get vaccinated to protect both yourself and others.

      This article is accurate as of press time. However, as the COVID-19 pandemic rapidly evolves and the scientific community’s understanding of the novel coronavirus develops, some of the information may have changed since it was last updated. While we aim to keep all of our stories up to date, please visit online resources provided by the CDC, WHO, and your local public health department to stay informed on the latest developments.

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