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How do vaccines work?

When a foreign infectious agent (bacteria, virus or toxins) enters our body for the first time, immune cells in our body identify it as an ‘enemy’ and generates an immune response in order to clear the infection. A key part of this immune response is the production of antibodies, which are proteins generated by immune cells, called B-cells, in our body specifically made to target the infectious agent. Some of these immune cells also have the ability to remember the infectious agent and can produce antibodies or directly kill infected cells next time that it invades our body, thus protecting us from reinfection and providing long-lived immunity (in some cases even life-long).


Vaccines contain a modified form or sub-parts of these infectious agents, providing a safer way for our bodies to build protection. As Dr. Anthony Fauci rightly describes: ‘to develop an effective vaccine, one should mimic natural infection, without causing disease.

Why should you get the vaccine?

1) Clinical trial results have demonstrated that COVID-19 vaccines in the United States are highly effective at preventing COVID-19 infection.

2) If you do get COVID-19, the vaccine may prevent you from getting very ill.

3) If you already have had COVID-19, you should still get the vaccine, as it may reduce your chance of being reinfected. There is currently not enough information about how long people are protected from COVID-19 after having it.

4) It protects those around you and helps to stop the spread in your community!

Why did the vaccine come out so quickly?

●  The mRNA vaccine technology, which is the platform used to develop the two vaccines currently approved by the Food and Drug Administration (FDA) for Emergency Use Authorization (EUA) in the United States, has been in development for decades

●  Scientists working on MERS and SARS research (other coronaviruses that have cause epidemics in the past) had previously identified the ‘Spike’ protein as a good target for the development of effective vaccines

●  Global collaboration of governments, multinational organizations, and scientists on producing the COVID-19 vaccine

●  Large, diverse participant groups volunteered for clinical trials


Safety of the vaccine:


The FDA granted Emergency Use Authorization (EUA) for the Pfizer vaccine on December 11, 2020. The Moderna vaccine was authorized on December 18, 2020.


Both vaccines have gone through a lengthy process of development and research before authorization. Clinical trials have included up to 50,000 participants. For reference, the FDS[JV4]  usually advises that trials include at least 3,000 participants.


Can you get infected with the COVID-19 virus from the vaccine?

NO, because the vaccine does not contain the COVID-19 virus. The Pfizer and Moderna vaccines contain synthetic mRNA, which provides instructions for your cells to generate the COVID-19 Spike protein, which by itself is harmless. The Spike protein is recognized by and stimulates our immune system to generate protective antibodies.


Data from and participants of clinical trials of the Pfizer and Moderna vaccines:

Efficacy rate

Similar effectiveness observed with different age, race, and ethnicity

95% protection from developing COVID-19 disease after 2nd dose 94.1% protection from developing COVID-19 disease after 2nd dose for Pfizer and Moderna, respectively.

Trial Participants:

  • Over 30,000 participants in each trial

  • 30+% were from minority groups

  • 10+% black, 10+% Latino

  • 45% 56-85 years old

What makes these trials a success?

The trials measured the percent of people who received the vaccines who went on to develop COVID-19 infection versus those who did not  receive the vaccine and got symptoms. 

Clinical Trial Data from:

1) Moderna's COVID-19 Vaccine Candidate Meets its Primary Efficacy Endpoint in the First Interim Analysis of the Phase 3 COVE Study. (2020, November 16). Moderna. Retrieved January, 2021, from

2) Pfizer and Biontech Conclude Phase 3 Study of Covid-19 Vaccine Candidate, Meeting All Primary Efficacy Endpoints. (2020, November 18). Pfizer. Retrieved January 26, 2021, from

3) Pfizer-BioNTech COVID-19 Vaccine. (n.d.). FDA U.S. Food & Drug Administration. Retrieved 2021, from


Side effects:

Side effects are normal and show that your immune system is working and is training to fight off any future COVID-19 exposures. People generally have longer lasting and more uncomfortable side-effects following the second shot.


Common side effects of Pfizer and Moderna vaccines reported during clinical trials:

  1. Pain at site of injection

  2. Fatigue

  3. Headache

  4. Muscle pain

  5. Joint pain

  6. Chills

  7. Fever

How the mRNA vaccines like Pfizer and Moderna work:

  1. COVID-19 mRNA instructs our cells to make a harmless version of the “spike protein” that is found on the surface of the COVID-19 virus.

  2. Our bodies know that the protein is foreign and as a result build antibodies that can fight against the virus.

  3. In case of future infection, these antibodies will remember how to fight the virus.

  4. These vaccines cannot give you COVID-19 and will not harm your DNA.

Protection by the COVID-19 vaccine:

  • It takes sometime after vaccination for you to receive the full protection from your vaccine. Your body needs time to train its immune system to recognize and fight COVID-19. It takes about 2 weeks after your final dose of the vaccine for full protection

  • It is possible to still get a COVID infection before this time, or even after your body has full-protection, but the vaccine will make these infections less severe and greatly protects against serious infection

What can I do after I am vaccinated?

  • Even after vaccination, it is still potentially possible to spread the virus of to get infected with a new strain, though these infections will be less severe. To protect yourself and your community, please continue to wear a mask and continue social distancing practices

  • While safety is important, the CDC has released new guidelines allowing more freedom to get together with other vaccinated individuals. Please check their page for the most recent updates

Where can I get vaccinated?

Vaccines are now available at pharmacies, hospitals, and local health department sites.

  • Contact your primary provider or pharmacy to see if they have started offering the vaccines.

  • Check out the NPR Vaccine Finder to see policies and availability in your state


How can I get to the vaccination center?

  • NYC - NYC DOHMH offers FREE transportation to and from City-run vaccination sites for people aged 65 and older who need transportation.

  • Many other states, cities, and organizations are also offering help with transportation to vaccination sites. Call 311 to learn about resources in your area

  • Please be sure to wear a mask and stay 6 feet away from others while at the vaccine site


Checklist of things-to-carry to your vaccination center:

  1. Appointment Confirmation 

  2. Proof of eligibility:

    1. Proof of age (one of the following)

      1. Driver's license or state ID

      2. Passport

      3. Birth certificate

    2. Proof of residency (any one of the following)

      1. Driver's license of state ID

      2. Utility bill

      3. Mails

    3. Employment proof for essential workers (healthcare workers, teachers, police officers, etc.)

NOTE: These are general guidelines. Check with your vaccination site for specific requirements

When can children get the vaccine?

  • The Pfizer vaccine is authorized for people 16 and older, and the Moderna vaccine is authorized for people 18 and older.

  • Trials in teenagers have just begun, and there are no current trials involving children under the age of 12.

  • Children have different immune systems than adults, and more research will be required to figure out the appropriate dose. It is not yet known when we can expect a vaccine for young children.

Common Myths about the COVID-19 Vaccine:

Myth: We do not know what is in the vaccines.

Fact: Pfizer and Moderna have published their ingredient lists for the vaccines. Ingredients include the COVID-19 mRNA for the harmless spike protein, fats that help deliver the mRNA to your cells, and other common ingredients that stabilize the vaccine.†


Myth: The COVID-19 can make someone infertile or impotent, harm a fetus, or hurt a baby breastfeeding from a mother who was vaccinated

Fact: Pregnant and breastfeeding women can get the COVID-19 vaccination. However, it is recommended that they speak with their medical provider first.†


Myth: I won’t need to wear a mask after I get vaccinated.

Fact: It will take a while for large amounts of people to get the vaccine. Although the vaccine may prevent you from getting ill, it is currently unknown if you are able to carry and transmit the virus to others when vaccinated. Thus, while more is being learned about how well the vaccine works, it is essential to wear a mask and to continue social distancing.

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