COVID-19 Vaccine Tracker
Phill Magakoe—AFP/Getty Images
January 7, 2021 6:00 AM EST

What kind of vaccine is it?

The vaccine uses a weakened cold virus to deliver genes for one of the COVID-19 virus’s key proteins, known as the spike protein—once in the cells, the viral protein activates the immune system. It’s a strategy that researchers have used in vaccines they are testing against Ebola and HIV. Unlike the shots from Moderna and Pfizer-BioNTech, Janssen’s vaccine only requires a single shot.

How does it work?

The immune system recognizes the viral spike protein as foreign and starts making antibodies and other immune cells to target it. If these cells then encounter a live virus, they can neutralize the virus and reduce the chance that it can infect cells and cause disease.

How effective is it?

In studies involving more than 43,000 people from eight countries that Janssen provided to the Food and Drug Administration to support a request for emergency use authorization, the vaccine was 66% effective in protecting people from COVID-19 disease. That included efficacy against new mutant versions of SARS-CoV-2, including ones first identified in South Africa and Brazil. In South Africa, for example, where the new variant is already the dominant source of infections, the vaccine was slightly less effective, 57%, in protecting people from getting sick. However ,the shot was 85% effective in preventing serious illness, which usually includes hospitalization and other intensive care, among people who were vaccinated compared to those getting a placebo.

Are there any side effects?

Most of the side effects reported in the study were mild to moderate, including injection site pain, headache, and fatigue. The FDA determined that some potential rash and clotting effects could also be related to the vaccine, but more studies are needed to evaluate those events.

How is it stored?

The vaccine can be shipped and stored under refrigerated conditions, between 2°C (35.6°F) and 8°C (46.4°C) for up to three months. Each vial contains five doses.

Where is it authorized?

The South Africa Health Productions Regulatory Authority authorized an early access program of the Janssen vaccine in that country for health workers on Feb. 12.

The U.S. FDA granted emergency use authorization for the vaccine on Feb. 27.

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