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  • Writer's pictureRuby Deubry

Top COVID-19 Vaccine Questions: A Deeper Understanding

Updated: Mar 2, 2021

Last update: March 2, 2021


Coronavirus overview

Coronavirus disease (COVID-19) is an infectious disease caused by a coronavirus called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). There are many different types of coronaviruses. SARS-CoV-2 is a novel virus meaning that, until December 2019, it never been seen before. On January 30, 2020, the World Health Organization (WHO) declared the COVID-19 outbreak a global health emergency.

COVID-19 causes upper airway (respiratory) infections. Main symptoms include fever, sore throat, dry cough, fatigue, and loss of smell or taste. Infection with COVID-19 can lead to systemic organ complications like heart and liver problems and can lead to death.

Persons can get infected with COVID-19 when they inhale viral droplets in the air from an infected person. Touching contaminated surfaces and then touching your face can also cause COVID-19. Symptoms may start 2 to 14 days after exposure to the virus, although symptoms typically appear within 4 or 5 days after exposure.

Several SARS-CoV-2 variants have emerged globally starting in the late Fall of 2020. These include the including the B.1.1.7, which emerged in the United Kingdom, the B.1.351 emerging from South Africa, and the P.1 variant that emerged in Brazil. Research is ongoing on the impact of the SARS-CoV-2 variants particularly on transmission rate, disease severity, and resistance to immunity.

How many vaccines are available?

There are currently 3 manufacturers with vaccines that have been approved for Emergency Use Authorization (EUA) in the United States (US):

  1. Pfizer, Inc., and BioNTech (Pfizer-BioNTech)

  2. ModernaTX, Inc. in partnership with the National Institue of Allergy and Infection Diseases (Moderna)

  3. Janssen: pharmaceutical companies of Johnson & Johnson

More vaccines have been approved in other countries, including the Oxford-AstraZenaca vaccine. And there are other vaccine candidates in Phase 3 development including the Novavax nanoparticle vaccine.

How does the mRNA vaccine work?

Both Pfizer-BioNTech and Moderna vaccines use messenger RNA (mRNA) technology. Although COVID-19 mRNA vaccines are the first of their kind to be produced and tested in large-scale human trials, mRNA technology has been studied for more than a decade.

Figure 1. Overview of mRNA vaccine technology. Accessed from

RNA (ribonucleic acid) are single-stranded molecules embedded with DNA instructions. There are different types of RNAs, each having various functions. mRNAs carry information on how to make proteins. An mRNA strand will carry instructions for making a single protein.

COVID-19 mRNA vaccines provide instructions for making the SARS-CoV-2 spike (S) glycoprotein, commonly known as the spike protein. The mRNA is enclosed in a lipid nanoparticle, which is a tiny bubble of fat. The lipid bubble protects the mRNA when it is injected and allows binding to our cells.

Once the spike protein is produced, the immune system will recognize the protein as foreign and the immune system should be triggered. Vaccines are considered a type of active immunity, which results in our body making antibodies. (Figure 1)

How do viral vector vaccines work?

Viral vectors have been studied for over 30 years. With viral vectors, a 'transport' virus is modified so it can no longer cause disease. In the case of the COVID-19 vaccine, the vector virus is an adenovirus, which typically causes the common cold.

The gene for the spike protein is inserted into the inactivated adenovirus. When the vaccine is given, the spike protein gene is delivered into our cells. Similar to the mRNA vaccine, our cells' machinery will create the spike protein, triggering an immune response, and creating antibodies.

Figure 2. Yellow highlighted area illustrates how the adenoviral vector functions. Adapted from on March 1, 2021.

Comparing Pfizer-BioNTech, Moderna & Janssen COVID-19 Vaccines

Table 1. Comparing the emergency use COVID-19 vaccines available in the US

Do the vaccines prevent or treat COVID-19?

The main (primary) purpose of the COVID-19 vaccines is to help prevent persons from getting infected with the disease. A secondary benefit is that the vaccine may help prevent severe symptoms if vaccinated persons do become infected with COVID-19.

How long does it take for the vaccines to be effective?

With any vaccine, it takes a few weeks for the vaccine to be fully effective. Many vaccines, like the flu vaccine, take 2 weeks to be effective. Protection is not immediate. Also, vaccines will not prevent you from getting the disease if you were infected prior to vaccination.

Both doses of the Pfizer-BioNTech and Moderna are required to reach 95% effectiveness. Pfizer-BioNTech doses are separated by 21 days, while Moderna doses are separated by 28 days. A reasonable estimate for the full benefit from the mRNA vaccines is 5 - 6 weeks from the first dose.

It is important to remember that the length of immunity after getting a COVID-19 vaccine is unknown. It is still vital to follow COVID-19 safety protocols.

What are the side effects of the vaccines?

Injection site pain (occurring in 66% - 90% of persons), fatigue (33% - 68%) and headache (25% - 63%) are the top 3 side effects reported by persons who received the mRNA vaccine. The risk of moderate side effects appears to be higher in younger persons (< 55 years old) and after the 2nd dose. Side effects typically started within 1 - 2 days of getting the vaccine and resolved 2 - 3 days later.

Other reported side effects include joint pain, muscle pain, chills, fever, nausea, and swelling at the injection site and under the arm.

A few cases of Bell's palsy of facial muscles occurred in the Pfizer-BioNTech, Moderna, and Janssen clinical trials. According to the National Institutes of Health (NIH), Bell's palsy affects about 40,000 people in the US each year. The number of incidences in the clinical trials was relatively similar. Thus, there is insufficient data to know if the vaccine causes Bell's palsy. Per the Advisory Committee on Immunization Practices (ACIP), persons with a history of Bell's palsy can still be offered the vaccine.

When can I get the vaccine?

There are two broad phases to the COVID-19 vaccine distribution: Phase 1 and Phase 2.

Phase 1 has three sub-phases: 1a, 1b, and 1c. Phase 1a supplies have been allocated to health care personnel and long-term care (LTC) residents and staff.

ACIP has provided recommendations and guidelines for allocating the COVID-19 vaccine during the remainder of the Phase 1 period. Allocation has been determined by job-type, age, and health status. The ACIP guidelines are not federally enforced; therefore, each state governs how the vaccine is distributed.

Phase 2: There is no information as yet on when the vaccine will be widely distributed to persons who do not meet Phase I eligibility. Refer to the health department in your state for the most up-to-date information.

Who should not get the vaccine?

Persons with a history of a severe allergic reaction or any type of immediate allergic reaction to any ingredient of the COVID-19 vaccine.*

Persons who have had a severe allergic reaction or any type of immediate allergic reaction after the first dose of the mRNA COVID-19 vaccine should not receive another dose.

Persons with an allergy to polysorbate. Polysorbate is not in the mRNA COVID-19 vaccines but is closely related to polyethylene glycol (PEG), which is a component of these vaccines.

*A severe reaction includes symptoms like difficulty breathing, fainting, and rapid heartbeat. Allergic symptoms like hives may also be present. Anaphylactic reactions often develop within 30 minutes of allergen exposure and progress rapidly. Immediate allergic reactions occur within 4 hours of getting the vaccine and may include symptoms such as hives and wheezing.

Pfizer-BioNTech ingredients: Page 2 of the Pfizer’s COVID-19 Vaccine Fact Sheet

Moderna ingredients: Page 2 of the Moderna’s COVID-19 Vaccine Fact Sheet

Should I get a COVID-19 test before getting the vaccine?

It is not necessary to have a test before getting the vaccine. The Centers for Disease Control and Prevention (CDC) recommends that persons can be vaccinated regardless of whether they had a prior infection.

If you had a COVID-19 infection, you may already have some protection by way of naturally-acquired active immunity (natural immunity). However, experts do not know how long natural immunity or vaccine-acquired immunity lasts. Therefore, persons should be offered the vaccine when it is available to them.

Should I stop my medication or supplements prior to the vaccine?

Prescription Medication

Persons should continue to take their regular prescription medication unless instructed otherwise by their doctor.

Of note is that the Pfizer-BioNTech, Moderna, and Janssen clinical trials included persons with one or more high-risk conditions that placed them at increased risk for severe complications of COVID-19. High-risk conditions included chronic lung disease, coronary artery disease, diabetes, liver disease, severe obesity, and HIV infection. These individuals would likely have remained on maintenance medication to treat their condition.

Persons on a blood thinner or those with a bleeding disorder should inform their vaccine provider before the vaccine is given. These persons are at a higher risk of bleeding or bruising with vaccine administration and a few extra steps may be needed to minimize excess bleeding or bruising. Persons should discuss with their doctor about medication management before getting the vacine.

Over-the-Counter (OTC) Medicine

Currently, the CDC does not recommend using OTC medicine just to prevent having side effects from the vaccines. Antihistamines (e.g. diphenydramine), non-steroidal anti-inflammatory products (e.g. ibuprofen), or anti-fever medicine (e.g.acetaminophen) should only be taken prior to the vaccine under doctor advisement. Medical experts are not certain how these OTCs affect the immune response but believe they could lessen the effectiveness of the vaccines. Antihistamines may mask allergy symptoms and delay diagnosis and management of anaphylaxis. These OTCs can be used for reactions, fevers and/or pain that occurs after vaccination, if appropriate.


There is currently no information on whether supplements interact with the COVID-19 vaccines. Based on the CDC recommendations for OTCs , it may be best to avoid supplements that could dampen the immune response or those that have antihistamine effects just prior to getting the vaccine.

More important is to maintain good nutrition and habits in general. This includes healthy foods, hydration, sleep, and exercise. Supplements may also play a role in supporting health. Talk to your doctor and follow their guidance on whether starting or continuing supplements is right for you.

Pregnancy Information

Pregnant women were excluded from the clinical trials. Therefore, there is not enough data to make conclusions on the safety of the COVID-19 vaccines in pregnancy.

Per the WHO, pregnant women who get COVID-19 are at a higher risk of having more severe illness than non-pregnant women. COVID-19 has also been associated with an increased risk of pre-term birth. Pregnant women who are at high risk of exposure to COVID-19 or those who have certain high-risk medical conditions, may be offered the vaccine during the initial vaccine distribution phase under the advise of their doctor.

Although COVID-19 vaccination of pregnant women is currently not recommended by some larger organizations, e.g. WHO, the vaccine should not be withheld from pregnant individuals who choose to receive the vaccine

If you are pregnant or breastfeeding, discuss your options with your healthcare provider.

Providers are encouraged to enroll pregnant patients exposed to COVID-19 vaccines in the Organization of Teratology Information Specialists (OTIS) pregnancy registry

How to report an adverse event

The Vaccine Adverse Event Reporting System (VAERS) is a US national vaccine safety surveillance program run by CDC and the Food and Drug Administration

If you are experiencing a medical emergency, seek immediate assistance from a healthcare provider or call 911.

Vaccine Adverse Event Reporting System (VAERS)

Where to find more information on COVID-19 vaccines


  1. FDA. Fact Sheets for Healthcare providers administering vaccine (vaccination providers) - Janssen. Available at: Retrieved February 13, 2021

  2. FDA. Fact Sheets for Healthcare providers administering vaccine (vaccination providers) - Moderna. Available at: Retrieved February 13, 2021

  3. FDA. Fact Sheets for Healthcare providers administering vaccine (vaccination providers) - Pfizer-BioNTech. Available at: Retrieved February 13, 2021

  4. Gavi vaccine alliance. Four types of COVID-19 vaccines. Available at: Retrieved February 13, 2021

  5. Harvard Health. If you've been exposed to the coronavirus. Available at: Retrieved on March 1, 2021

  6. John Hopkins Medicine. New Variants of Coronavirus: What You Should Know. Available at: Retrieved on February 16, 2021

  7. Merryn Voysey et al. Safety and efficacy of the ChAdOx1 nCoV-19 vaccine (AZD1222) against SARS-CoV-2: an interim analysis of four randomised controlled trials in Brazil, South Africa, and the UK. The Lancet. 2021; 397: 99–111.

  8. Norbert Pardi, et al. mRNA vaccines — a new era in vaccinology. Available at Retrieved on February 16, 2021

  9. Regulatory Affairs Professionals Society. COVID-19 vaccine tracker. Available at: Retrieved Feb 13, 2021

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