What Is the Difference Between the Pfizer, Moderna, and Johnson & Johnson COVID-19 Vaccines?

Over the past year and a half, the world has experienced a deadly pandemic — COVID-19. In the face of such a challenge, pharmaceutical companies around the world quickly started developing vaccines to help slow the spread of the virus and to bring an end to the coronavirus pandemic. So far, one of these vaccines has been granted FDA-approval — Pfizer’s Comirnaty. Two others have been authorized for use in the U.S. — Moderna and Johnson & Johnson.

Here we’ll compare the three COVID-19 vaccines and the differences in how they work, their effectiveness, and what side effects you can potentially expect from each. 

How do the COVID-19 vaccines work?

Vaccines work by triggering the cells in your body to make antibodies — memories created in response to an infection — against a certain germ. This means that if you are exposed to the germ in the future, you’ll be better prepared to fight it.

The processes and technology used to make vaccines vary. And while several different types of COVID-19 vaccines are being researched, we’ll cover the two types currently available in the U.S. — mRNA and viral vector vaccines.

Johnson & Johnson vs. Moderna and Pfizer vaccine

At a glance, there are a few key differences between the vaccines from Johnson & Johnson, Moderna, and Pfizer.

*Specific percentages showing vaccine effectiveness can vary by study as well as specific factors being studied (e.g., effectiveness against preventing moderate-to-severe COVID-19 symptoms vs. against hospitalization and death)

mRNA vaccines

The mRNA vaccines — Pfizer and Moderna — work by using a technology called messenger RNA (mRNA). You can think of mRNA as a blueprint that is delivered to cells in your body. The cells in your body already use mRNA as instructions to make proteins that they need, but the mRNA contained in the vaccines is specific to the coronavirus that causes COVID-19. 

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How do mRNA vaccines cause an immune response?

When you receive a dose of a mRNA vaccine, your cells get the blueprint for making part of the coronavirus, called the spike protein. Spike proteins are found on the surface of the coronavirus, and they help the virus enter and infect your cells. They’re only one small part of the virus, so you cannot get COVID-19 from the vaccine itself.

After you’re vaccinated with a mRNA vaccine, your body creates antibodies against the spike protein. This allows your body to build up its immunity. In other words, your body will already know how to better fight off the coronavirus if you’re ever exposed in the future.

What happens to the mRNA in my body?

After your body receives the spike protein blueprints, the cell breaks down the mRNA. But while it’s there, it only interacts with the part of the cell responsible for making proteins (called ribosomes), and it never enters the nucleus of your cells — which contains your DNA. Therefore, it will not affect your DNA.

Is mRNA technology safe?

Although these vaccines were developed faster than most others have been, it doesn’t mean that they’re unsafe. Both mRNA vaccines have been shown to be safe and effective during clinical trials, and this still holds true after about 400 million doses have been administered in the U.S. 

And while the mRNA technology is relatively new to the market, it’s been researched for decades. In fact, the use of mRNA vaccines has been gaining interest among scientists in recent years because they are quicker to develop than traditional vaccines. 

Viral vector vaccines

Viral vector vaccines — like the Johnson & Johnson vaccine — use a harmless virus (called a viral vector) to deliver a message to your cells. They have been researched to treat or prevent many health conditions, and the technology has even been used for an Ebola vaccine. But in the case of the COVID-19 vaccines, they deliver instructions for making the coronavirus spike protein.

How do viral vector vaccines cause an immune response?

When you receive a dose of the viral vector COVID-19 vaccine, the harmless virus enters your cells and gives the message to start producing spike proteins. They work similarly to the mRNA vaccines in that after the viral vector prompts your cells to make spike proteins, your immune system will start making antibodies against them. This helps to create protection against the coronavirus. 

Can the virus in the vaccine make me sick?

The Johnson & Johnson vaccine uses an inactivated adenovirus — a common cold virus that’s been engineered so that it can’t make you sick — as its viral vector. It’s a less common adenovirus (called adenovirus type 26) since using one that most people have been exposed to could result in the vaccine being less effective. And like with the mRNA vaccines, you cannot get COVID-19 from the viral vector vaccine.

Johnson & Johnson vs. Moderna and Pfizer vaccine effectiveness

While it’s easy to get caught up in the clinical trial effectiveness numbers, the bottom line is that each of the COVID-19 vaccines has been shown to be effective — especially at preventing severe illness resulting in hospitalization or death. 

Next, we’ll review how the vaccines performed in clinical trials, how effective they are in the real world, and when you can expect to be fully protected after getting vaccinated.

Pfizer

The Pfizer COVID-19 vaccine requires two doses, given 3 weeks (21 days) apart. If needed, the second dose can be given later than that. There is no maximum time limit between the first and second doses. But the closer you are to 3 weeks apart, the better. Immune response varies from person to person, but you are considered fully protected 2 weeks after receiving the second dose.

In clinical trials, the Pfizer vaccine was shown to be 95% effective at preventing symptomatic COVID-19 infections in people ages 16 and older. The vaccine was also tested and authorized for use in adolescents ages 12 to 15, showing it to be 100% effective against getting an infection.

Real-world effectiveness data is also encouraging. Pfizer’s vaccine has been shown to be 93% effective at preventing hospitalization from COVID-19 for up to 6 months after the second dose. There is concern that Pfizer’s protection may start to fade slightly after 6 months. However, studies are still being conducted on how much this effectiveness drops.

Based on this data, though, the FDA has authorized a booster shot of Pfizer’s Comirnaty at least 6 months after the second vaccine dose for the following people:

• Adults aged 65 and older

• Adults between ages 18 and 64 who have a higher risk of severe COVID-19 (e.g., people with weakened immune systems)

• Adults between ages 18 and 64 who work in a setting where they may be frequently exposed to COVID-19 (e.g., frontline healthcare workers)

Moderna

The Moderna COVID-19 vaccine also requires two doses, but they’re given 4 weeks (28 days) apart. Similarly, you’ll need to wait at least 2 weeks after the second shot to be considered fully vaccinated. You’re also able to get the second dose later than 4 weeks after the first dose, if needed.

In clinical trials, the Moderna vaccine was shown to be around 94% effective at preventing symptomatic COVID-19 infections in people ages 18 and older who received both doses.

Similar to Pfizer, real-world studies are showing Moderna’s vaccine is highly effective. A recent study showed that two doses of the Moderna vaccine is 93% effective at preventing COVID-19 hospitalization. Another study found that — unlike Pfizer — Moderna’s effectiveness didn’t fade in the months following the second dose. Researchers will continue to monitor this.

Given the potential risk of fading protection, though, the FDA did authorize a booster dose of Moderna at least 6 months after the second shot for the following people:

• Adults aged 65 and older

• Adults between ages 18 and 64 who have a higher risk of severe COVID-19 (e.g., people with weakened immune systems)

• Adults between ages 18 and 64 who work in a setting where they may be frequently exposed to COVID-19 (e.g., frontline healthcare workers)

Johnson & Johnson

Unlike the mRNA vaccines, the Johnson & Johnson COVID-19 vaccine initially only requires one dose, making it a more convenient option for many people. You’re considered fully protected 2 weeks after you receive the vaccine.

It may seem as though that the Johnson & Johnson vaccine is less effective than the mRNA vaccines, but it’s important to know that they are difficult to compare head-to-head. A number of factors could contribute to the differences, like what the studies were measuring and the prevalence of coronavirus variants when the vaccines were being tested.

That said, in clinical trials, the Johnson & Johnson vaccine was about 66% effective at preventing symptomatic COVID-19 infection 14 days after the vaccination. However, it was about 85% effective at preventing severe disease (hospitalization and death) at least 28 days after the vaccination.

Real-world studies paint a slightly different picture than clinical trials, though. Current studies show Johnson & Johnson’s vaccine is about 71% effective at preventing hospitalization. 

The FDA and CDC have now recommended a second dose of the Johnson & Johnson vaccine at least 2 months after the initial shot. This booster is authorized for all adults over 18 who received one dose of the Johnson & Johnson vaccine.

Why do the Pfizer and Moderna vaccines require two doses?

The mRNA vaccines require two doses in order to build an ideal immune response. There are two types of cells involved in forming immunity from a vaccine  — B cells and T cells. While the first vaccine dose helps these cells recognize the coronavirus, the second dose helps the immune system produce a stronger response.

You may be wondering if one shot will give you enough protection if you’re partially vaccinated. The short answer is no. You won’t be effectively protected if you skip your second shot. Because neither Pfizer nor Moderna studied how effective a single dose was in clinical trials, we don’t know how long that partial protection would last either. So it’s recommended to get both doses. If you’re eligible to get a third or booster dose, that’s also recommended. 

Why do the Pfizer and Moderna vaccines have different waiting periods between the first and second shot?

The time interval between the first and second shot is determined by the data collected from their clinical trials. The companies have published their safety and efficacy results based on these specified intervals. Pfizer’s published data is based on a 21-day interval between doses, while Moderna’s is based on a 28-day interval. 

Johnson & Johnson vs. Moderna vs. Pfizer: Who can get the COVID-19 vaccines?

If you have certain types of allergies — to the vaccine ingredients or other vaccines — the CDC has recommendations for whether or not you should get the shot. But for most other people, it’s recommended that you get vaccinated. And while there are some general guidelines across all COVID-19 vaccines, the biggest difference is which age groups can get each vaccine.

Adults

All three COVID-19 vaccines can be given to people who are at least 18 years old. But the Moderna and Johnson & Johnson vaccines are currently only authorized for use in this age group — meaning these two vaccines can only be given to individuals 18 and above. 

Children

The Pfizer vaccine is authorized for anyone at least 12 years old. They’ve also requested that the FDA expand this age group to include children as young as 5. The FDA is scheduled to make a decision on the 5 to 11 year-old age group at the end of October 2021.

Moderna completed their adolescent vaccine trials and reported the vaccine is about 93% effective for children between 12 and 17 years old. They submitted their authorization request to the FDA in June 2021. But no decision has been made yet.

Johnson & Johnson’s adolescent vaccine trial is ongoing. While the study is planned to continue until March 2022, there may be initial results available by December 2021. Currently, it’s too early to say how effective their vaccine is for adolescents under 18 years old.

Johnson & Johnson vs. Moderna vs. Pfizer vaccine side effects comparison

Most vaccines have the potential to cause minor side effects, and the COVID-19 vaccines are no exception. Each of the vaccines cause similar side effects to each other. It’s also more likely that younger adults will experience these common side effects.

Due to the high-profile nature of the coronavirus pandemic, you may have some concerns about side effects that you’ve heard about in the news. Let’s break down what you can expect.

Common side effects

All three COVID-19 vaccines have the potential to cause a reaction in the injection arm including:

• Soreness

• Redness

• Swelling at injection site

These injection site reactions were reported more frequently in Pfizer’s and Moderna’s clinical trials than Johnson & Johnson’s. For example, around 90% of people 18 and older reported pain at the injection site during Pfizer’s and Moderna’s vaccine trials. This is compared to about 60% of adults under 60 in Johnson & Johnson’s studies. 

Similarly, around 75% of adults 56 and older and 80% of adults 65 years and older experienced pain at the injection site after taking the Pfizer and Moderna vaccine, respectively. In contrast, only around 33% of adults 60 and older who took the Johson & Johnson vaccine reported feeling pain at the injection site.

All three vaccines can also cause mild flu-like symptoms, such as:

• Headache

• Fatigue

• Body aches

• Mild fever

• Chills

• Nausea

These side effects tend to be mild to moderate in severity and only last for a few days. And if you’re receiving an mRNA vaccine, the side effects tend to be stronger after the second shot. The extent of side effects can vary depending on your age and which vaccine you’ve received.

Side effects for younger people from clinical trials include:

Side effects for older adults from clinical trials include:

It’s important to remember that people can react to the vaccines differently — some may react strongly, whereas others won’t react at all. And if you don’t experience any side effects, that doesn’t mean that the vaccine doses aren’t working.

Serious side effects

Overall, all three of the COVID-19 vaccines have been well-tolerated with temporary side effects. However, more serious side effects can sometimes happen. Here’s a few that you should know.

Severe allergic reactions

A severe allergic reaction after a COVID-19 vaccine is rare. But if you do have one after the first dose, the CDC recommends that you not get the second dose of the same vaccine. 

A severe allergic reaction, also known as anaphylaxis, requires the use of epinephrine and possibly a trip to the hospital. This is why the CDC recommends that everyone who receives a COVID-19 vaccine should be monitored for 15 minutes afterward — this is when most severe allergic reactions tend to happen. 

But if you have a history of anaphylaxis from any cause, or if you’ve had an immediate reaction after a different vaccine or injectable medication, you should be monitored for 30 minutes.  

Severe arm pain

The CDC has received rare reports of “COVID arm” after receiving the first shot of a COVID-19 vaccine. This is a red, swollen, itchy, and potentially painful rash on the injected arm that can sometimes cover a large area. It can occur a few days to more than a week after your vaccination. 

It’s still recommended to get the second dose if you experience this, but let your vaccinator know when you go for your second shot.

Johnson & Johnson vaccine blood clot risks

There have been reports of a rare but serious blood clotting disorder after receiving the Johnson & Johnson vaccine. After a brief pause in April 2021 and expert review, the CDC and FDA agree that this vaccine is still safe to use. 

However, if you receive the Johnson & Johnson vaccine, you should be on the lookout for the following symptoms for a few weeks after your shot:

• Shortness of breath

• Blurred vision

• Severe headache that won’t go away

• Leg swelling

• Chest pain

• Abdominal pain that won’t go away

• Bruising or blood spots under the skin away from the injection site

Pfizer’s and Moderna’s myocarditis and pericarditis risks

Both Pfizer’s and Moderna’s vaccines have been linked to a higher risk of two heart conditions: myocarditis and pericarditis. Both of these conditions involve inflammation of different parts of the heart and can lead to problems with how the heart pumps blood. Adolescents and young males are more at risk for these complications.

Myocarditis and pericarditis typically happen within several days of getting vaccinated and more often after the second dose. Thankfully, these side effects are extremely rare. The World Health Organization (WHO) reported that for every million second doses given of mRNA vaccines, about 40 young men experience myocarditis or pericarditis.

If you do receive an mRNA vaccine, you should keep an eye out for the following symptoms:

• Chest pain

• Trouble breathing

• Feeling like your heart is racing or pounding

• Fevers that don’t go away

• Swelling in your legs or feet

Contact your healthcare provider if you experience any of the above shortly after receiving a dose of either the Pfizer or Moderna vaccine.

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Written by:

Sarah Lobello Pearson, PharmD

Sarah Pearson is a practicing pharmacist with over 10 years of experience in the field. She received her doctorate in pharmacy from the University of Georgia in Athens, GA.

Edited by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Reviewed by:

Christina Aungst, PharmD

Christina Aungst, PharmD, is a pharmacy editor for GoodRx. She began writing for GoodRx Health in 2019, transitioning from freelance writer to editor in 2021.

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