Table of Contents
How safe is the vaccine?
The vaccine safety trials showed that, outside of minor side effects that are common with other vaccines, the Moderna and Pfizer vaccines are extremely safe. However, it has been reported that individuals with a history of severe allergies (i.e. anaphylactic shock) should take precaution when getting the vaccine. The Pfizer and Moderna vaccines do not contain the virus, and the contents of the vaccine are similar to normal chemicals made by our cells. Therefore, the vaccine is considered extremely safe. For example, the lipid envelopes enclosing the vaccine contents are simple phospholipids just like your normal cell’s membranes. The RNA is released inside your cells, where it is used to make a protein in the same way all your proteins are made. None of the vaccine components can change your DNA. Per CDC recommendation, pregnant women should consult their doctor proper to being vaccinated, as there are currently no data from clinical trials looking at either Moderna or Pfizer vaccine safety in pregnant women. The World Health Organization currently advises that pregnant women not take either mRNA vaccines until those clinal trials are done.
Will I get sick from the COVID-19 vaccine?
The Moderna and Pfizer vaccines do not contain any viral material, therefore you will not be infected with the virus. The second dose of these COVID-19 vaccines does generate a very strong immune response that may cause you to have mild soreness and temporary lethargy. In clinical trials, people typically demonstrated minor side effects following the second-dose of the vaccine, including low-grade fever, soreness at the infection site, fatigue, chills and nausea/vomiting. These side effects typically last 1-2 days after vaccination. In very rare cases, people with a history of severe allergic reactions have had more serious adverse effects. Therefore, people in this group should consult their doctor prior to receiving a vaccine.
What is in the Moderna COVID-19 vaccine?
The Moderna COVID-19 vaccine is composed of lipid nanoparticles (LNPs), ribonucleic acid (RNA) and several commonly used ingredients that maintain the stability of the vaccine. Here is a complete list of Moderna vaccine contents:
- Lipid nanoparticles (LNPs): SM-102, 1,2-dimyristoyl-rac-glycero3- methoxypolyethylene glycol-2000 [PEG2000-DMG] and cholesterol: Make up the lipids that resemble our cell’s phospholipids and allows for cellular entry.
- Ribonucleic Acid (RNA): Genetic material that is used by our cells to create the Coronavirus Spike protein.
- Tromethamine and Tromethamine hydrochloride: Buffer to maintain the vaccine at a neutral pH.
- Acetic acid: Antimicrobial agent commonly used in food preservatives.
- Sodium acetate: Buffer commonly used in food preservatives.
- Sucrose: Common table sugar used to stabilize vaccine.
Has mRNA technology been around long enough for it to be safe in humans?
Although the Pfizer and Modera COVID-19 vaccines are the first mRNA vaccines approved by the FDA for human use, the use of mRNA to generate an immune response in animal models dates back over 30 years, and has been researched extensively. Lipid nanoparticles utilized in the vaccine also have been researched in animal models for several years. Prior to the COVID-19 pandemic, there were already mRNA vaccines for other viruses in Phase I and II trials.
To get the vaccine approved so quickly were there short cuts taken during the approval process?
There were no short cuts taken for approval of the COVID-19 vaccine. In order to be approved by the FDA, each drug must undergo three Clinical Trial Phases. These phases are typically done in sequential order, with increasing numbers of test subjects in each, with each trial typically taking months to years to complete, depending on the drug examined. However, for the COVID-19 vaccines, the Phase 2 and 3 trials were “stacked”, allowing for expedition of the normal approval process. However, the same number of subjects were enrolled for the trials that are normally required, and the same safety and effectiveness standards were applied when compared to other approved vaccines.
How long does it take to generate a protective immune response to COVID-19 after the vaccine?
Full protection is acquired two weeks after the second dose of the mRNA vaccine (Pfizer or Moderna). Although, the first dose does offer some protection 14 days after vaccination (~80% for the Moderna), how long that protection lasts is currently unknown. It typically takes the body 14 days to begin to generate an effective antibody response. Therefore, if you are infected with SARS-Cov-2 during that period, you may not be fully protected from COVID-19.
If I get my first dose from Moderna, can I use Pfizer for the second dose or vice versa?
No, this is not recommended. Although both vaccines use similar materials, as well as the same mechanism to provide protection (see next question), no data has been examined to determine the safety of using one of each vaccine for doses. Therefore, if you are vaccinated with either Moderna or the Pfizer vaccine on the first dose, you are required to be vaccinated with the same on the second dose either 28 days (Moderna) or 21 days (Pfizer) post vaccination.
How does the mRNA vaccine (Pfizer or Moderna) protect me from COVID-19?
The mRNA vaccine contains a lipid nanoparticle that helps protect the mRNA. This lipid nanoparticle fuses with the lipids that surround our cells, releasing a mRNA inside of our cells. mRNA is then recognized by our normal cellular machinery responsible for creating our body’s proteins and make the SARS-CoV-2 Spike protein. The Spike protein is then released from the cell, where it is picked up by immune cells and used to generate an immune response. This results in the generation of SARS-Cov-2 Spike protein-specific neutralizing antibodies, as well SARS-Cov-2-specific CD8 T cells. This process takes up to 14 days to occur. However, upon infection with the virus, the antibodies and CD8 T cells are able to interact with the virus very quickly after infection to produce a much stronger and efficient immune response, protecting the vaccinated individual from the severe symptoms of COVID-19.
Why do I still have to wear a mask even after vaccination?
Although the vaccine trials have demonstrated protection from COVID-19-related illnesses, they have not been shown to prevent infection. Therefore, it is possible that even though you are vaccinated, or have recovered from COVID-19, you may still be able to become infected as well as pass the virus to others. As the vaccine is being rolled out, different populations of people will be vaccinated at different times. Therefore, until the vast majority of people have had a chance to be vaccinated, we must do our part to limit any potential spread that may occur, first and foremost by wearing face coverings in public settings at all times.
How long will my protection last from the vaccine?
This is currently still under study, but it is estimated that protection will last at least a year. Therefore, the vaccine may require yearly boosters.
If I have already had COVID-19, do I need to get vaccinated?
Yes. Even if you already have had COVID-19, you should still get vaccinated. At this point, it is unclear how long natural immunity lasts to COVID-19, and there have been several documented cases of reinfection. Additionally, some studies have suggested that vaccination may confer stronger immunity than natural infection. Therefore, it is recommended that even if you have been infected, you should get vaccinated. There is no recommended time period after infection that you need to wait before vaccination. If you were previously treated with passive antibodies (i.e., convalescent plasma), you must wait 90 days after treatment before getting vaccinated or else the vaccine may not be effective.
Will the COVID-19 vaccine be more effective than the seasonal influenza vaccine?
Recent studies for both the Pfizer and Moderna vaccines have shown no significant decrease in protection to the the UK strain (B.1.1.7). However, in both vaccines, there is a slight decrease in protection to the South African strain (B. 1.351), with protection still expected to be enough to prevent severe disease (i.e., hospitalization). Moderna has already created a booster specifically for the South African strain that is currently entering the initial stages of clinical trials. Research is currently being done for the newly discovered Brazilian strain (P.1). While it is possible for viruses to evolve resistance to vaccines, there is currently no evidence suggesting that this has occurred. However, the sooner that widespread vaccination occurs and the number of infected people spreading the virus is reduced, the fewer opportunities the virus will have to evolve resistance to current vaccines. Viruses can’t mutate if they can’t replicate! For this and others reasons, rapid vaccination of as much of the population as possible is critical to stopping the COVID-19 pandemic.
Will the Pfizer and Moderna vaccines work against new mutant strains of SARS-CoV-2?
Although SARS-CoV-2 has mutated over the course of the pandemic, none of the mutant strains, including the UK and South Africa variants, have been shown to evade the protection provided by the mRNA vaccine. While it is possible for viruses to evolve resistance to vaccines, there is currently no evidence suggesting that this has occurred. However, the sooner that widespread vaccination has occurred and number of infected people spreading the virus is reduced, the fewer opportunities the virus will have to evolve resistance to current vaccines. For this and others reasons, rapid vaccination of the as much of the population as possible is critical to stopping the COVID-19 pandemic.
Should I delay getting a vaccine myself to make sure people at higher risk get it first?
While this sentiment is well-intentioned, the vaccine campaign will be most effective if people take the vaccine as soon as it becomes available to them. The prioritization of vaccine subjects is decided at the managerial and policy level by government and health care professionals, and the sooner that large swaths of the population are vaccinated, the lower the risk of contracting COVID-19 will be for everyone. Even if you are young and healthy, getting vaccinated will likely reduce the chance that you could infect others unknowingly.
*Please note that throughout this document, “SARS-CoV-2” refers to the virus, and “COVID-19” refers to the respiratory disease caused by virus.
For more information about the Moderna Vaccine, including its contents and safety profile
and its contents, please visit the Moderna website, the FDA website and/or the CDC website:
For considerations about using different vaccines, or if you have had COVID-19 before, please visit the following link.
For more information on mRNA and Lipid Nanoparticles technology, please see the following articles:
How the Moderna vaccine works:
How the nine coronavirus vaccines work:
More vaccine questions answered: