With the Feb. 27 authorization by the U.S. Food and Drug Administration (FDA) of a one-dose COVID-19 vaccine developed by Johnson & Johnson, Americans will now have three vaccines available to combat the coronavirus infection. J&J is expected to soon begin shipping out up to 4 million doses now that has received its emergency use authorization (EUA).

The Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices will meet Sunday and Monday to recommend whether and how the J&J vaccine should be distributed.

The three available vaccines use two different technologies to achieve the same end — to trigger immune responses in our cells that will allow our bodies to make antibodies to the spike protein located on the surface of the coronavirus. Those antibodies will help fight a COVID-19 infection if the real coronavirus enters our body.

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The Pfizer-BioNTech and Moderna vaccines use the same basic technology, known as mRNA, to provide the genetic code our cells need to produce the antibodies. These vaccines essentially teach our cells how to make a protein that prompts an immune response without using the live virus that causes COVID-19.

The J&J vaccine also delivers a genetic code to our cells, but does it in a different way. This vaccine uses what’s called an adenovirus — a harmless virus that can no longer replicate — to basically send the genetic message to our cells. And the adenovirus goes into the nucleus of our cells and uses our DNA to send the genetic code.

So the main difference between the two vaccine technologies is that the Pfizer-BioNTech and Moderna vaccines use mRNA to get the genetic instructions to our cells, while the J&J vaccine uses DNA.

Beyond the different technologies used to send our immune system the key to fighting off COVID-19, there are differences among the three vaccines authorized in the U.S., particularly when it comes to the temperatures at which they are stored, the number of doses required, how they are administered and the timetables for when patients need to get their shots.

How effective are they?


  • Vaccine was shown to be 95 percent overall effective in preventing symptomatic COVID-19 after two doses in phase 3 clinical trials.
  • Vaccine was shown to be 94.7 percent effective in people age 65 and older in its clinical trials after the second dose.


  • Vaccine was shown to be 94.1 percent overall effective in preventing symptomatic COVID-19 in its phase 3 clinical trials after the second dose.
  • Vaccine was shown to be 86.4 percent effective in people age 65 and over after two doses.

Johnson & Johnson

  • Vaccine was shown to be 66.1 percent overall effective in preventing COVID-19 symptoms after one dose in its phase 3 multi-country clinical trials and 72 percent effective among participants in the U.S. trials.
  • Vaccine was shown to be 68.6 percent effective in people age 65 and over after one dose.

Significance: All three vaccines more than meet the 50 percent effectiveness threshold required by the FDA. In addition, the data from phase 3 clinical trials for all three vaccines show that all of them are 100 percent effective in preventing hospitalization and death from COVID-19.

Vaccines have different temperature requirements


  • Vaccine has been shipped in special containers filled with dry ice that can maintain a temperature of less than minus 94 degrees Fahrenheit and has been stored in cold-storage units at that temperature. The FDA recently agreed to let Pfizer ship and store its vials for two weeks at higher temperatures — from minus 13 degrees to minus 5 degrees Fahrenheit.
  • Vials may be placed in a regular refrigerator for up to five days. The vaccine must be used between 30 minutes and two hours once it’s thawed to room temperature.


  • Vaccine can be shipped and maintained at standard freezer temperatures of minus 4 degrees Fahrenheit.
  • Vials may be stored in a standard freezer for up to six months.
  • Vaccine can stay in a standard refrigerator for up to 30 days. The vaccine must be used within 12 hours once it’s at room temperature.

Johnson & Johnson

  • Vaccine can be shipped and maintained at standard refrigerator temperatures of 36 degrees to 46 degrees Fahrenheit.
  • J&J can ship and store the vaccine at the same temperatures and there’s no need for thawing.
  • Unopened vials can be kept outside the refrigerator at room temperature for 12 hours; punctured vials can be kept for six hours.

Significance: The J&J vaccine is the easiest to transport and store because it requires only standard refrigeration. The Moderna vaccine doesn’t need to be transported and stored in as cold a temperature as the Pfizer-BioNTech product.

Preparation varies slightly


  • Once the vial is thawed, the vaccine must be diluted with saline, which is basically salt water, before it can be injected.

Moderna and Johnson & Johnson

  • These vaccines come ready to be administered. No dilution required.

Significance: Having to dilute a vaccine is not uncommon. For example, when health care providers give the measles vaccine, they dilute it.

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Who can take vaccine?


  • People 16 years old and older

Moderna and Johnson & Johnson

  • People 18 years old and older

Significance: Those under 18 likely won’t be eligible to get the vaccine until later in 2021 anyway since health care workers, nursing home residents and staff, essential workers, people 65 and older and those with certain health risks are slated to be the first groups vaccinated. Other vaccines may be available to younger age groups by then.

Side effects


  • The most common side effects were pain at the injection site, followed by tiredness, headache, muscle pain, chills, joint pain and fever, according to the FDA.
  • In the United Kingdom, two health care workers reported severe allergic reactions (anaphylaxis) after being vaccinated; two health care workers in Alaska reported a serious allergic reaction after receiving the Pfizer-BioNTech vaccine.
  • In the U.S. trial, four people who received the vaccine developed Bell’s palsy, which causes usually temporary paralysis in facial muscles


  • The most common side effects were pain at the injection site, followed by tiredness, headache, muscle pain, joint pain and chills, an FDA analysis found.
  • Three trial participants who received the vaccine developed Bell’s palsy.

Johnson & Johnson

  • The most common side effects were pain at the injection site, followed by headache, fatigue and myalgia (muscle pain).
  • There was one case of hypersensitivity — although not classified as anaphylaxis — that began two days after the injection.
  • There were four reported cases of Bell’s palsy: two among those getting the vaccine and two who received the placebo.

Significance: The side effects are similar for each vaccine. William Moss, a physician and executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health, points out that the number of Bell’s palsy cases in both trials is “very small and likely just represents chance,” but says “going forward we’ll just need to monitor more carefully and just make sure we’re looking for Bell’s palsy and make sure that it’s not related to the vaccine.”

When it comes to the anaphylactic reactions exhibited in Great Britain, one of the participants had a history of allergic reactions. U.S. federal officials have warned health care providers not to give the vaccine to anyone with a known history of a severe allergic reaction to any part of the vaccine, a standard caution for all vaccines. As with the Bell’s palsy cases, officials are expected to watch for such reactions.

How many shots?


  • Two shots of the vaccine, given 21 days apart, are required for it to be fully effective.


  • Two shots are required, 28 days apart.

Johnson & Johnson

  • One shot required.

Dena Bunis covers Medicare, health care, health policy and Congress. She also writes the “Medicare Made Easy” column for the AARP Bulletin. An award-winning journalist, Bunis spent decades working for metropolitan daily newspapers, including as Washington bureau chief for the Orange County Register and as a health policy and workplace writer for Newsday.


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