Everything you need to know about the COVID-19 vaccines available now

Last updated: Nov 3, 2021
Learn how the three approved shots stack up and find out why all of them can help keep you safe.

Pfizer-BioNTech came first. Moderna followed a week later. Then more recently, Johnson & Johnson’s COVID-19 vaccine received authorization for emergency use by the U.S. Food and Drug Administration (FDA).

Starting with a nurse in New York City who received the first dose in the U.S. in December, nearly 100 million Americans have been fully vaccinated against COVID-19 as of late April, according to the Centers for Disease Control and Prevention (CDC). More than 40% of adults have received at least one dose. Plus, starting November 2, 2021, every Californian age 5 and older became eligible to get their shot. (Visit My Turn to learn how to schedule yours.)

Having not one but three new vaccines in less than a year is a scientific feat worth celebrating. Here’s a closer look at how the available COVID-19 vaccines work, and how they keep you safe.

The mRNA vaccines: Pfizer-BioNTech and Moderna

How do they work?

The goal of any vaccine is to teach your immune system what a particular germ looks like. That way, if the real virus or bacteria enters your body later, your immune system will know how to fight it off. Traditional vaccines use inactive or weakened germs to trigger this kind of response.

Vaccines for COVID-19 take a totally different approach. They do not contain any part of the coronavirus. Instead, they use a type of genetic material called messenger RNA — or mRNA — to deliver a set of instructions to your cells. This blueprint tells your cells to start making spike proteins. These spikes look just like the ones on the actual coronavirus.

These spike proteins are completely harmless. But when your immune system sees these spikes, it starts producing antibodies to fight them off. This is the part where your immune system learns what COVID-19 looks like and how to attack it. If you’re exposed to the real coronavirus later, your body will know exactly what to do to prevent you from getting sick.

Once the mRNA instructions are delivered, your cells break them down and dispose of them. The messenger RNA has absolutely no contact with your own DNA and does not change it.

How many doses are required?

For Pfizer-BioNTech: two shots, 21 days apart

For Moderna: two shots, 28 days apart

You’re considered fully protected two weeks after your second dose of either vaccine.

Are they effective?

Yes, very. Both the Pfizer-BioNTech and Moderna vaccines have been shown to be highly effective in preventing infection, according to the latest real-world data published by the CDC. Earlier findings showed the shots work well in people of different ages, genders, races, and ethnicities. And they’re safe and effective for most people with underlying medical conditions.  

Scientists are still learning how well the vaccines work against new variants. According to the CDC, early data shows that the shot might work against some variants but could be less effective against others. More research is needed.

On very rare occasions (two to five people per million vaccinations), mRNA vaccines have appeared to trigger anaphylaxis, a severe but treatable allergic reaction. That’s why the CDC requires that you be monitored for 15 minutes after your shot. If you have a history of severe allergies, you’ll be watched for 30 minutes.

The new vaccines are based on decades of research. Read more about the science behind them.

The viral vector vaccine: Johnson & Johnson

How does it work?

Viral vector vaccines use a modified version of a different virus to deliver important instructions to your cells. The Johnson & Johnson COVID-19 shot uses an adenovirus, a type of virus that causes the common cold. This “vector” has been changed so that it can’t replicate and make you sick.

Once the vector enters your cells, it starts churning out harmless spike proteins. Your immune system spots them and gets to work making antibodies.

As with the mRNA vaccines, this one has no contact with your DNA.

How many doses are required?

One. You’re considered fully protected two weeks later.

Is it effective?

Yes. It also prevents most moderate to severe illness from COVID. In the clinical trials, the Johnson & Johnson vaccine prevented hospitalizations and deaths from COVID-19 100% of the time.

According to researchers, protection from the Johnson & Johnson vaccine was generally consistent across race and various age groups of adults. It was also shown to work against multiple variants.

Very rarely, this shot may cause blood clots along with low platelets. The condition occurs in about 7 in 1 million vaccinated women under age 50, according to the CDC. Because of this, experts are recommending that you watch for the follow symptoms for three weeks after receiving this vaccine:

  • Severe or persistent headaches or blurred vision
  • Shortness of breath
  • Chest pain
  • Swelling
  • Persistent abdominal pain
  • Easy bruising or tiny blood spots under the skin beyond the injection site

Although it’s unlikely, you’ll experience these signs, it’s important to seek medical care quickly if you do.

What are the routine side effects from the shots?

The three vaccines have similar potential side effects. The most common include:

  • Pain at the injection site
  • Headache
  • Fatigue
  • Muscle aches
  • Nausea

Most were mild and lasted a day or two; the reactions were less common in older adults.

The bottom line

All three of the vaccines help prevent serious illness and death if you do get COVID-19. It’s one of the most important steps you can take to protect yourself from COVID-19 and help stop the pandemic. If you’re unsure about which vaccine to get, talk to your doctor.


The information in this story was accurate as of press time and posting. Getting vaccinated is one of the best ways to limit the spread of the coronavirus. It’s also important to continue practicing social distancing (keeping at least 6 feet away from people outside your household) and washing your hands frequently. You should also be appropriately masked any time you’ll be in public. According to the CDC’s latest guidance, this means layering a disposable mask underneath a snug-fitting cloth mask or placing a mask fitter over your cloth mask to ensure a tight fit. Because the situation surrounding COVID-19 continues to evolve, we encourage readers to follow the news and recommendations for their own communities by using the resources from the CDCWHO, their local public health department and our COVID-19 member site

Ready to get vaccinated? Find a location and schedule an appointment.

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