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Early Data Shows Johnson & Johnson COVID-19 Vaccine Produces Is 66% Effective

Johnson & Johnson logo on building.

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Key Takeaways

  • Johnson and Johnson’s one-shot coronavirus vaccine produced an immune response against COVID-19 in clinical trials.
  • Clinical trials say the vaccine is 66% effective at preventing moderate to severe disease 28 days after vaccination, and 72% effective in the U.S.
  • The one-shot vaccine would be an asset to the current U.S. vaccination process, which currently requires logistical planning for vaccines that require two doses.
  • If the company’s vaccine is authorized by the United States Food and Drug Administration (FDA), it would be the third vaccine approved for use in the U.S.

The latest results from a Phase 3 clinical trial show Johnson and Johnson’s one-shot coronavirus vaccine is 66% effective against moderate to severe COVID-19.

The results are reflective of the vaccine's effectiveness globally, and show levels of protection are different around the world. While the vaccine was 72% effective among participants in the U.S, it was only 57% effective among participants in South Africa, where a highly-transmissible SARS-CoV-2 variant first emerged.

Notably, nobody in the clinical trial needed to be hospitalized for COVID-19, and nobody died of the disease.

While the overall effectiveness is lower than the 95% demonstrated by both Moderna and Pfizer, the Johnson & Johnson vaccine brings with it two promising factors that Moderna’s and Pfizer’s two-dose vaccines do not have: the first being that healthcare facilities will face less logistical planning when administering a one-dose versus a two-dose vaccine. The vaccine can also be kept in the refrigerator for three months, as opposed to Moderna’s and Pfizer’s vaccines, which must be stored in a freezer up until use, making preservation challenging for some healthcare facilities. 


Earlier this month, results from Phase 1/2a clinical trials indicated that the company's vaccine induced immune responses against SARS-CoV-2, the virus that causes COVID-19, in both young and elderly participants.

According to the report, Johnson & Johnson randomly assigned healthy adults between the ages of 18 and 55 and those 65 and older to receive either a high or low dose of the vaccine, or a placebo. A select group of participants in the 18-to-55 cohort received a second dose of the vaccine. In total, the trial included 805 participants.

“Most of the volunteers produced detectable neutralizing antibodies, which researchers believe play an important role in defending cells against the virus, after 28 days, according to the trial data,” said a Johnson & Johnson statement. “By day 57, all volunteers had detectable antibodies, regardless of vaccine dose or age group, and remained stable for at least 71 days in the 18-to-55 age group.”

The company is working with its pharmaceutical arm, Janssen, to develop the vaccine.

What Is an Immune Response? 

Developing an immune response is a necessary step in the process of creating vaccines. Put simply, when it is introduced to a new virus, the immune system will respond by employing a number of germ-fighting tools needed to get over the infection, according to the Centers for Disease Control and Prevention (CDC). After the infection clears up, the immune system will “remember” what it learned about how to protect the body against that disease, and employ that against any future infections.

"Your immune system protects you against disease," says Soma Mandal, MD, a board-certified internist in New Jersey. "When the immune system (composed of various organs) recognizes a particular germ (e.g. bacteria, viruses) as foreign, it launches antibodies that help destroy the germ."

Mandal says this process is referred to as B-cell immunity.  T- cell immunity, on the other hand, occurs when "the immune system remembers a particular germ and destroys it before it can make you sick again."

Vaccines operate similarly, except they are designed to imitate an infection, meaning the immune system remembers and protects without a person becoming ill in order to do so, Mandal says. Of course, minor symptoms may occur as a result of a vaccine.

Johnson & Johnson’s Early Results

In October, Johnson & Johnson announced early results showing that a single dose of their vaccine could induce antibodies in 97% of study participants that effectively neutralized the virus in the laboratory, but the company still required additional information on the effectiveness of the vaccine.

Then, they experienced a setback in their trials when a participant experienced an unexplained illness. No specific details were provided about what happened due to patient privacy. Regulators determined on October 23 the event was not related to the vaccine and the trial was safe to resume.

Evaluating Safety

Participants in all three groups (high-dose, low-dose, and placebo) of the clinical trials reported mild symptoms, including:

  • Headache
  • Fatigue
  • Nausea
  • Myalgia (muscle pain)
  • Pain at the injection site

Adverse reactions were less common in the older age group. In the case of the participants who received the two-dose regimen, fewer reactions occurred after the second dose.

Five participants experienced more serious symptoms, with one participant visiting the hospital for a fever associated with vaccination—the participant recovered within 12 hours. The remaining four cases were confirmed to be unrelated to the vaccine.

Next Steps

The company’s chief science officer Paul Stoffels, MD, said in an interview on January 12 that Johnson & Johnson is on target to deliver one billion doses of its vaccine by the end of this year. Stoffels said until the company receives an emergency use authorization (EUA) from the U.S. Food and Drug Administration (FDA), it is still too early to say specifically how many doses would be available in March. Before moving forward with an EUA, the FDA requires a follow-up of at least two months of safety data on half of the study participants, a threshold Johnson & Johnson crossed earlier this month.

“If the single-dose vaccine is shown to be safe and effective, the company expects to submit an application for Emergency Use Authorization with the U.S. Food and Drug Administration shortly afterward, with other regulatory applications around the world to be made subsequently,” Johnson & Johnson said in their news release.

“We are aiming for 1 billion doses in 2021,” Stoffels said. “If it is a single dose, that means 1 billion people. But it will be in a ramp-up throughout the year...It’s a few weeks too early to be giving final numbers on what we can launch in the first couple months.”

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  4. Centers for Disease Control and Prevention. Understanding Vaccines. Updated July 2018.

  5. Johnson & Johnson. Johnson & Johnson Posts Interim Results from Phase 1/2a Clinical Trial of its Janssen COVID-19 Vaccine Candidate. Updated October 4, 2020.

  6. Janssen. Johnson & Johnson Prepares to Resume Phase 3 Ensemble Trial of Its Janssen COVID-19 Vaccine Candidate in the U.S. Updated October 23, 2020.

  7. U.S. Food and Drug Administration. Emergency Use Authorization for Vaccines Explained. Updated November 11, 2020.