With the U.S. Food and Drug Administration's emergency-use authorization of a single-dose COVID-19 vaccine developed by the Janssen Pharmaceutical Cos. of Johnson & Johnson in late February, U.S. residents who want to get inoculated against the coronavirus now have three vaccines to choose from—each with varying degrees of efficacy.

The latest emergency use authorization is the third such authorization issued by the FDA in as many months. According to the FDA, emergency use authorizations allow unapproved medical products or unapproved uses of approved medical products to be used in an emergency, including a national health crisis such as the ongoing coronavirus pandemic, when there are no adequate, approved and available alternatives.

The Feb. 27 authorization of Johnson & Johnson's Janssen COVID-19 vaccine follows the emergency use authorizations of other coronavirus vaccines manufactured by Moderna on Dec. 18 and by Pfizer and BioNTech on Dec. 11.

"The authorization of this vaccine expands the availability of vaccines, the best medical prevention method for COVID-19, to help us in the fight against this pandemic, which has claimed over half a million lives in the United States," acting FDA Commissioner Dr. Janet Woodcock said in a Feb. 27 statement. "The FDA, through our open and transparent scientific review process, has now authorized three COVID-19 vaccines with the urgency called for during this pandemic, using the agency's rigorous standards for safety, effectiveness and manufacturing quality needed to support emergency-use authorization."

According to the Centers for Disease Control and Prevention, Pfizer-BioNTech's and Moderna's vaccines—both two-shot vaccines—have higher efficacy rates for preventing illness than the single-shot Johnson & Johnson vaccine; the vaccine efficacy rates stand at 95%, 94.1% and 66.3%, respectively.

Additionally, Pfizer-BioNTech's and Moderna's vaccines are both mRNA vaccines, while Johnson & Johnson's Janssen vaccine is a viral vector. According to the CDC, mRNA vaccines are a new type of vaccine that protects against infectious diseases without putting a weakened or inactivated germ into the body to trigger an immune response. Instead, mRNA vaccines instruct cells to make the "spike protein," which is found on the surface of the virus that causes COVID-19. By contrast, viral vectors use a modified version of a different, harmless virus—not the virus that causes COVID-19—to deliver those same instructions to cells in the body.

Despite their differences, the three vaccines also have similarities: All three options are administered via a shot in the muscle of the upper arm and have similar side effects, including pain, redness and swelling at the site of the shot, as well as tiredness, headache, muscle pain, chills, fever and nausea throughout the rest of the body. Additionally, none of the vaccine options can give someone COVID-19.

For all three vaccines, most side effects are mild to moderate, beginning within a day or two of getting the vaccine and subsiding within a few days. For two-shot vaccines, side effects are more common after the second dose of the vaccine.

Additionally, none of the vaccines contains eggs, preservatives or latex, and a complete list of ingredients in the Pfizer-BioNTech, Moderna and Johnson & Johnson vaccines can be found online.


According to the CDC, people are considered fully vaccinated two weeks after their second dose in a two-dose series, such as the Pfizer-BioNTech or Moderna vaccines, or two weeks after a single-dose vaccine, such as Johnson & Johnson's vaccine.

Once a person is fully vaccinated, there are certain things the CDC permits that would not be recommended for an otherwise unvaccinated person.

According to a March 8 CDC update, once a person is fully vaccinated, he or she can gather indoors with fully-vaccinated people without wearing a mask and gather indoors with unvaccinated people from one other household without masks, unless any of those people or anyone they live with has an increased risk for severe illness from COVID-19.

Additionally, if a fully vaccinated person has been around someone who has COVID-19, they do not need to stay away from others or get tested unless they have symptoms.

However, several COVID-19 precautions will remain in place for the foreseeable feature regardless of vaccination status.

"We're still learning how vaccines will affect the spread of COVID-19," the March 8 CDC update said. "After you've been fully vaccinated against COVID-19, you should keep taking precautions in public places like wearing a mask, staying 6 feet apart from others, and avoiding crowds and poorly ventilated spaces until we know more."

In addition to these precautions, the CDC recommends those who are fully vaccinated to continue to avoid medium- and large-sized gatherings, delay domestic and international travel, continue to watch out for COVID-19 symptoms and follow local guidance.