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COVID-19 Vaccine: Answering questions about the Pfizer and Moderna vaccines, safety, side effects and more
General Wellness

COVID-19 Vaccine: Answering questions about the Pfizer and Moderna vaccines, safety, side effects and more

By Your Health staff
Posted: January 11, 2021

The first phase of COVID-19 vaccination administration is underway. The phased approach begins with health care workers first, followed by vulnerable populations, and ultimately the general public.

We want to provide you with important information about the vaccine, the distribution plan and what it means for you and your loved ones. We know you may have many questions, so we’ve identified several of the most frequently asked questions to address here.

Though we expect the COVID-19 vaccine to have a significant impact on the pandemic, it will take time for enough people to be vaccinated to make a difference. In the meantime, continue to wear your mask, wash your hands and social distance.

We’ll continue to keep you up-to-date on new developments.


Is this a live virus vaccine?

No. This is an mRNA (messenger RNA) vaccine. mRNA vaccines do not contain any actual or live virus. Instead, they contain an inactive copy of part of the COVID-19 genetic code (the mRNA) . Once the vaccine is injected into someone’s arm muscle, it is taken inside their immune cells where the mRNA is used to make a harmless piece of a protein that resembles part of COVID-19. Once this protein piece is made, our immune cells break down the mRNA that was injected in the vaccine and eliminate it from our body. After this, our immune system sees this new protein and recognizes it as something that should not be in our body and immediately begins building an immune response.  Because this protein is a copy of part of the COVID-19, this immune response results in our bodies being protected against future infections if exposed to the actual virus. . 

Does the vaccine contain preservatives?

There are no preservatives of any type  in the Moderna and Pfizer vaccines. Both vaccines contain very few ingredients: the mRNA, a fat molecule to help the mRNA get into our immune cells, and various sugar and electrolyte solutions to help the vaccine from breaking down inside the vial.

How long is the period between the first and second doses?

Both vaccines are given as two doses. The first dose is called a “priming dose” to start the immune response needed to prevent COVID-19 infection. The second dose is called a “booster” to help build the final layer of protection and increase the full potential of our immune system to fight off the virus.  For the Pfizer vaccine, the second dose is given 21 days after the initial vaccination, with the Moderna vaccine having 28 days in between the two shots.

The first “priming” dose might not provide the highest levels of immunity, so the second “booster” dose is needed to provide the best level of protection from COVID-19. Data from Pfizer shows the level of protection from the first dose is 52% but after the second dose, that level increases dramatically to 95%. For the Moderna vaccine, the first dose is estimated to provide up to 80% protection and 94% after the second dose. 

It is important to remember that elderly patients may not receive the same level of protection as seen in the clinical trials due to changes in how their immune system responds with increased age. Because of this, it is very important that patients receive both doses of the vaccination as recommended by the FDA. 

Does the second dose need to be given exactly on day 21, or is day 22 or 23 okay?

For optimal vaccine protection, it is important that you complete the vaccine series.You should receive the second dose as close to the designated timeframe as possible. However, there is a small range for the second dose. The FDA recommends a 4-day grace period of 4 days earlier than the recommended date for the second dose, which would be 17 days for the Pfizer vaccine and 24 days for the Moderna vaccine.  If a second dose is given after the desired due date, there is no need to restart the vaccination series.  

How effective is the vaccine?

Trials of the Pfizer vaccine demonstrated that patients received 95% protection from a COVID-19 infection after one full week has passed since their second vaccine was administered.  For the Moderna vaccine, trials found 94.1% protection after two full weeks have passed since receipt of the second vaccine dose. 

Once you have both doses, how long are you protected from the virus?

We won’t know how long immunity lasts until we have more data on how well it works. Both natural immunity and vaccine-induced immunity are important aspects of COVID-19 that experts are actively researching and learning more about. Right now, makers of the vaccine estimate this protection will last several years and hope to provide more evidence as they continue to study people enrolled in the trials.  

How is the vaccine different from monoclonal antibody infusions?

The vaccine is a means of prevention, and monoclonal antibody infusions are a form of treatment.

The vaccine uses mRNA technology, which encodes the viral protein. When injected, the muscle cells translate the genetic instructions and put the viral protein directly in the body. This gives the immune system a preview of the real virus without causing disease. Instead, it, allows the immune system to develop antibodies that can neutralize the real virus if a person ever becomes infected, and this is how it is so effective in preventing infection.

Monoclonal antibody therapy is used in people who are at high risk for developing severe disease, but aren’t sick enough to be hospitalized with COVID-19 and don’t require oxygen therapy due to COVID-19. This type of treatment binds to the surface of the virus and prevents it from getting into a person’s cells.


If I already had COVID, am I eligible for the vaccine?

Due to the severe health risks associated with COVID-19 and the fact that re-infection with COVID-19 is possible, people are advised to get a COVID-19 vaccine even if they have already had COVID-19.

At this time, the CDC is recommending that anyone with known current COVID-19 infection should not get the vaccine until the person has stopped having symptoms and they have been removed from quarantine.

Current evidence suggests that it is uncommon for a person to become reinfected within the 90 days after the initial infection. Because of this, the FDA has recommended that people may consider delaying receipt of the vaccine until near the end of this 90 day period. 

I got the first dose of the COVID-19 vaccine, but then I tested positive for COVID-19. Can I still get the second dose?

At this time, the CDC is recommending that anyone with known current COVID-19 infection should not get the second vaccine dose until the person has stopped having symptoms and they have been removed from quarantine.  Current evidence suggests that it is uncommon for a person to become reinfected within the 90 days after the initial infection. Because of this, the FDA has recommended that people may consider delaying receipt of the second vaccine dose until near the end of this 90 day period, if they desire to do so. 

Would those with egg allergies be able to receive the vaccine?

Yes. Because the currently available COVID-19 vaccines use mRNA to build an immune response, they do not involve egg products in their manufacturing like some currently available vaccinations, like influenza, do. 


When will it be distributed to the public?

The vaccine will likely be available to the general population in spring or summer of 2021, but that remains to be determined. With limited quantities available at this time, the plan across the country is to vaccinate health care workers first, followed by vulnerable populations such as nursing home residents.

This is why it is critically important that we all continue following infection prevention practices, such as consistently wearing a mask, frequently washing our hands, avoiding crowds, and staying home when we feel sick.

When it is available to the public, who will oversee the vaccine distribution?

All vaccines will be ordered through the Centers for Disease Control (CDC). The CDC has worked with state, tribal, territorial and local jurisdictions across the country on the vaccination plan for their respective areas. The CDC has also worked with private partners, such as chains and networks of independent pharmacies, and other federal agencies on plans to more widely distribute COVID-19 vaccines. For example, the CDC is working with specific pharmacies to offer on-site COVID-19 vaccination services for residents in long-term care settings.


What are the side effects?

It is important to remember that most of the things people think of as “side effects” from the COVID-19 vaccine are actually normal effects that occur after receiving an immunization. These effects are commonly referred to as “immunogenic effects.”

Because our body sees the protein that is created as a result of the mRNA vaccine as foreign, it builds an immune response that consumes a great deal of energy within our bodies. This may result in a person feeling tired/run down — or for their body to ache for a short period of time. In some individuals, it may even result in a fever.

Overwhelmingly, the most common complaint from people enrolled in the clinical trials was a sore muscle at the site they received the injection. 

No serious adverse side effects have been associated with the COVID-19 vaccines. While there were several individuals in the clinical trials who developed a mild, temporary inability to move facial muscles, patients on both sides — those who received the vaccine and those who received the placebo — reported this and the FDA has not concluded that the vaccination caused this to occur. 

What if a person has had an allergic reaction to other medications? 

If a person has had a previous severe, anaphylactic reaction to a vaccine in the past, they should discuss with their doctor about reviewing the COVID-19 vaccine.

However, severe allergies to medications that are not vaccines do not mean a person cannot receive the COVID-19 vaccination. There is also no latex included in the vaccine packaging, so people with latex allergies are able to receive the COVID-19 vaccines, as well.

The CDC does recommend that people with a history of an immediate allergic reaction of any severity to a vaccine or an injectable drug — or a person with a history of anaphylaxis to any substance — should be observed for 30 minutes after receiving the COVID-19 vaccine.  

Are there any long-term unknowns?

Currently, more than 70,000 patients are being studied in clinical trials that began nearly six months ago and no long term effects have been reported. Researchers will continue to evaluate these patients for a long period of time and the FDA has committed to releasing information on any side effects that occur.

It is important to remember that out of all the vaccines approved by the FDA, a severe side effect has never developed more than two months after receiving a vaccine. This is one of the reasons the FDA required that patients enrolled in the trials were studied for two full months before the vaccines were evaluated for approval to administer to the general public.  

Vaccines are held to a very high standard of safety, since they're given to a very large number of people. So, although we can never rule out very rare side effects, we can rest assured that if this vaccine is approved by the FDA, it is safe enough for you to take.

How do we know that the side effect symptoms aren’t actually COVID symptoms? How are they different?

Some symptoms overlap and there is a possibility to contract COVID-19 before the vaccine takes effect. This may cause us to push for COVID-19 testing if symptoms are presented regardless of supposed cause. It typically takes a few weeks for the body to build immunity after vaccination. That means it’s possible a person could be infected with the virus that causes COVID-19 just before or just after vaccination. This is because the vaccine has not had enough time to provide protection. Testing is now widely available, so if in doubt about any symptoms you may experience, we encourage testing.


Can women who are currently pregnant or breastfeeding take the vaccine?

It is recommended that pregnant or lactating women discuss the vaccine with their provider.

Once I have received both doses of the COVID-19 vaccine, can I stop wearing a mask and social distancing?

It will take several months before everyone can receive the vaccine so it is important to continue infection control protocols.


Hearing from our infectious disease physician would be helpful.

On November 24, Dr. Shirin Mazumder, an infectious disease expert with MLH, conducted a media briefing answering many questions about the vaccines, including the differences between the Pfizer and Moderna vaccine and any potential side effects of the vaccines. You can watch that briefing below:


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