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The new vaccine requires only one shot.

Millions of people have received the coronavirus disease 2019 (COVID-19) vaccines made by Moderna and Pfizer. Yet, most Americans are still waiting for to get a vaccine. Fortunately, more vaccines are on the way.

On February 4, Johnson & Johnson filed an emergency use authorization application with the FDA for their COVID-19 vaccine. This means we may soon have a third option.

You may be wondering about the differences between the vaccines and which one is best for you. Here are six things we know about the Johnson & Johnson vaccine.

1. It teaches your immune system to recognize and destroy the coronavirus.

Different vaccines work in slightly different ways. The Johnson & Johnson shot uses a weakened common cold virus, called an adenovirus, as a vehicle to deliver a single coronavirus gene into human cells. That gene then provides the instructions for making the SARS-CoV-2 spike protein. When the body makes the spike protein, the immune system reacts by making antibodies. Later, if exposed to COVID-19, the immune system remembers what the spikes look like and how to destroy them.

It’s important to know: The adenovirus has been genetically modified so that it cannot duplicate. It cannot give you a cold or COVID-19.

“The Johnson and Johnson vaccine uses a vector to get the information into the person being vaccinated so the immune system will recognize it and build an immune response in order to protect that person,” says UNC Health Chief of Infectious Diseases Joseph J. Eron Jr., MD.  “It’s a little different than the current Pfizer and Moderna vaccines, but it’s the same kind of idea: it gets that message inside the body so that the body can see it and respond.”

2. It’s a one-dose vaccine.

The Johnson & Johnson vaccine requires only one shot. The current available vaccines require two doses.

Only needing one dose could make a difference in getting as many people vaccinated as possible, Dr. Eron says. “It’s easier to only have to do it one time.”

This vaccine is also easier to store and ship because it does not require super-cold storage like the current vaccines. This means the vaccine can be used in more rural areas or areas that may not have a place to store them, Dr. Eron says.

3. It is very effective in preventing severe disease.

In clinical trials, the Johnson & Johnson vaccine has been shown to be 85 percent effective in preventing severe disease that caused people to have to go to the hospital as well as death. When it comes to these most serious cases, the Johnson & Johnson vaccine “was very, very similar to the Moderna and Pfizer vaccines in protecting people from serious illness,” Dr. Eron says. “The studies suggest that it’s about 70 percent effective in keeping people safe.”

In other words, 7 out of 10 people are protected against getting the virus. The Moderna and Pfizer vaccines protected 9 out of 10 people.

“It sounds better to be 9 out of 10, but the protection from serious disease is very, very similar to the vaccines that we have already,” Dr. Eron says.

4. It is more effective against some COVID-19 variants than others.

Viruses are constantly changing, creating new versions—called variants.

“The virus’ job is to infect as many people as possible. It changes over time, so it can still spread, and that’s what we worry about,” Dr. Eron says.

Variants from Britain and South Africa have are different from what we have seen before. For example, the British variant appears to spread more easily. Researchers are working to understand whether serious COVID-19 disease is more common with these variants.

“As best we can tell, the Johnson & Johnson vaccine protects as well from the variant that’s appeared in England as it does for the most common variant in the United States,” Dr. Eron says. ““However, in South Africa, while the Johnson & Johnson vaccine still worked and appeared to prevent serious illness at a fairly high rate, it was less effective at preventing infection from the South African variant. So that is a concern and something that we are paying very careful attention to.”

5. The new vaccine may be available in the United States in the coming weeks.

We should know within the next few weeks if Johnson and Johnson will receive emergency authorization use for its vaccine in the United States. Before the FDA will do this, it must reanalyze the clinical trial data.

“FDA scientists and statisticians review the data and see if they can reproduce the results using the data from the company. It’s a very rigorous assessment,” Dr. Eron says. “It may be a little bit slower, but it gives me comfort about the safety of a vaccine.”

6. If you’re eligible for a vaccine now, you shouldn’t wait.

If a vaccine becomes available in the United States, it means it has been through every stage of clinical trials that would normally take place for a vaccine. It is very important to understand that it is not possible to get a vaccine into humans without taking all the necessary steps.

“Millions of people have been vaccinated and we ‘re getting a very good sense of in the safety of these vaccines,” Dr. Eron says. “Getting vaccinated sooner rather than later is better. It’s so important to be vaccinated to protect yourself. We believe that if enough people get the vaccine, there’ll be less infection in the community. When this happens, it will be better for everyone.”

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