The Johnson & Johnson COVID-19 Vaccine: What We Know So Far


The US Food & Drug Administration is currently reviewing a COVID-19 vaccine developed by medical manufacturer Johnson & Johnson. If approved, the Johnson & Johnson vaccine will become the third vaccine approved to prevent COVID-19 in the US alongside Moderna and Pfizer-BioNTech.

As the US continues to fight a vaccine shortage, the potential approval of a new vaccine is welcome news. But it’s also natural to have concerns—will this new vaccine be safe? And how effective will it be? 

Florida Medical Clinic Orlando Health’s Chief Medical Officer and infectious disease specialist Dr. Emilio Dominguez returns to answer your most commonly asked questions about the Johnson & Johnson vaccine and provide the latest advice on how to keep you and your family safe.

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1. When will the Johnson & Johnson vaccine be available? 

On February 4, 2021, Johnson & Johnson applied to the Food & Drug Administration (FDA) for emergency use authorization. The FDA announced it would review the results of Johnson & Johnson’s Phase III trials and make a decision on February 26, 2021.

If the shot is approved, it could be available for some as early as March 2021. The company hasn’t announced specific distribution dates, but it does have a contract with the US government for 100 million doses.

If authorized, the vaccine will likely be distributed according to Centers for Disease Control and Prevention (CDC) guidelines, which prioritizes frontline health care workers and those living in assisted care facilities.

2. How is the Johnson & Johnson vaccine different from Moderna and Pfizer? 

The Johnson & Johnson vaccine is notable because it only requires one dose, rather than two doses like the Moderna and Pfizer vaccines. The Johnson & Johnson vaccine can also be stored at typical refrigerator temperatures instead of requiring special freezers.

The Johnson & Johnson shot is an adenovector vaccine. It contains a tiny piece of coronavirus DNA that’s been “killed” (modified) so that it can’t replicate inside your body. By injecting you with a “dead” virus, your body can learn how to make antibodies to protect you against it without you having to get sick. This is the same way that the measles and flu vaccines work, but it’s different from how mRNA vaccines like Moderna and Pfizer work.

3. How safe is it?

Johnson & Johnson recently released the results of a Phase III clinical trial that included 43,783 participants. Half of these participants received the active vaccine, while the other group received a placebo (inactive vaccine).

The trial did not find any significant safety concerns relating to the vaccine. No anaphylaxis (severe allergic reaction) was observed in either group. However, like any vaccine, the Johnson & Johnson vaccine can cause side effects. The most common side effects are: 

  • Fever
  • Fatigue
  • Headache
  • Pain at the injection site 

These side effects typically resolve on their own 24 to 48 hours after receiving the vaccine. 

4. How effective is the new Johnson & Johnson vaccine? 

On January 29, 2021, Johnson & Johnson announced that their vaccine is about 66% effective overall in preventing COVID-19. However, the effectiveness varied depending on the country it was tested in.

In trials in the US, the vaccine was found to be around 72% effective at preventing COVID-19. In Latin America, it was 66% effective. In South Africa, it was 57% effective. 

This may be due to different strains of the coronavirus that are impacting different countries around the world. Scientists are still studying to see how special mutations in these new virus strains affect COVID-19 immunizations. Overall, those who were infected with COVID-19 after receiving the vaccine tended to have milder symptoms and lower rates of hospitalizations than those who weren’t vaccinated.

Learn more about the new coronavirus strains:

5. How many doses of the Johnson & Johnson shot do you need? 

The Johnson & Johnson vaccine is a single-dose medicine. This is in contrast to the Moderna and Pfizer-BioNTech vaccines, which both require two doses spaced a few weeks apart to be fully effective.

Johnson & Johnson is testing if adding a second booster dose could increase the effectiveness of their shot. But as of mid-February 2021, there is no plan to add a second dose.

6. How long does it take to build immunity?

You will not be instantly immune from COVID-19 after receiving a shot. The vaccine only provides maximum protection 2 weeks after receiving the second dose of the Moderna or Pfizer vaccines or a single dose of the Johnson & Johnson vaccine.

Furthermore, immunity isn’t 100% guaranteed—no vaccine is completely effective against COVID-19. That means it’s rare but possible to develop COVID-19 even after getting vaccinated. However, those who do develop the coronavirus after being vaccinated generally tend to experience milder symptoms. 

We don’t know how long COVID-19 immunity will last after receiving the vaccine, but scientists are certain that immunity from the vaccine outlasts the short-term protection someone gets after surviving COVID-19. In other words, don’t think you’re protected because you’ve recovered from COVID-19—the only long-term protection is through a vaccine.

7. Can you transmit COVID-19 after getting vaccinated?

You may be asking yourself this question if you or a loved one have received a shot but the rest of your family hasn’t. But, unfortunately, there isn’t a clear answer to this question yet. Scientists aren’t sure if you can still carry and transmit the virus after receiving a vaccine.

COVID-19 vaccines work by neutralizing the effect of the virus in your body, preventing you from getting sick or lessening symptoms if you do fall ill. That means they can help you from getting COVID-19 if you’re exposed but does not necessarily mean it can prevent you from spreading it asymptomatically (without symptoms).

You may still be able to transmit the virus to others, but doctors and scientists are still collecting data to learn more about transmission.

In the meantime, you should continue wearing a mask, washing your hands, and social distancing even after you receive the vaccine. That’s still the best way to keep yourself and others safe.

8. Should you wait to receive the Johnson & Johnson vaccine?

You may be wondering if it’s okay to wait for the single-dose Johnson & Johnson vaccine instead of the two-dose Moderna or Pfizer shots, but it’s advised that you should get whichever vaccine is available as soon as it is offered to you.

That’s because it’s not guaranteed that Johnson & Johnson will receive emergency use authorization from the FDA. If it does, it may not be available in your area for some time. 

It may seem like a hassle to receive two doses, but it’s better for you, your family, and your community to get vaccinated as soon as possible with whichever vaccine is first available to you.

Get Notified About the Vaccine Near You

Florida Medical Clinic Orlando Health plans to distribute the vaccines at our Hillsborough and Pasco offices as soon as they become widely available. We’re not sure when that will be just yet, but experts estimate around late Spring or early Summer 2021.

In the meantime, go to to learn about eligibility requirements and to make an appointment at a distribution location near you.

We’ll continue to provide updates on COVID-19 here on the Florida Medical Clinic Orlando Health blog and through our e-newsletter, which you can sign up for here. Remember to keep an eye on your local news outlets for the latest information about the coronavirus in your area.

Disclaimer: This blog is not intended to substitute professional medical advice. Always talk with your doctor before starting or stopping medications or treatments.



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