Covid Vaccines 101

This detailed overview compares the efficacy and common adverse effects for the COVID-19 vaccines.

June 10, 2021

Covid Vaccines 101

What do I need to know about the Covid-19 vaccines?

Currently, there are three (3) COVID-19 vaccines authorized for the prevention of COVID-19. These vaccines have met rigorous safety and efficacy criteria before approval. The safety of the vaccines is being continuously monitored through multiple systems. Vaccine efficacy represents the percent (%) reduction in the occurrence of the disease. Just like any other vaccine, COVID-19 vaccines do not give you the disease. Two (2) doses are needed for both mRNA vaccines (Pfizer-BioNTech and Moderna) and one (1) dose is needed for the DNA vaccine (Johnson and Johnson (Janssen)). It is important to keep a record of which vaccines you received as they are not interchangeable and have different immunization schedules. Your healthcare provider will provide you with a record of which vaccine was administered and schedule a follow-up appointment for the second dose if applicable. Recently, in New York State, a COVID-19 Pass (Excelsior Pass) has been launched to keep a record of your COVID-19 vaccine status. The best COVID-19 vaccine is the first one that is available to you; do not wait for a specific brand.

Name BNT162b2 mRNA-1273 JNJ-78436735
Manufacturer Pfizer-BioNTech Moderna, Inc. Johnson and Johnson (Janssen Pharmaceutials)
  • Two (2) doses
  • Intramuscular injection
  • Given 21 days apart
  • Two (2) doses
  • Intramuscular injection
  • Given 28 days apart
  • One (1) dose
  • Intramuscular injection
Approved age group 12 years and older 18 years and older 18 years and older
  • In the clinical trial, the vaccine was about 95% effective in the overall population
  • In the elderly (≥ 65 years old), the vaccine was about 94.7% effective
  • Against severe COVID-19, the vaccine was about 75% effective at least 7 days after the 2nd dose
  • In the clinical trial, the vaccine was about 94.1% effective in the overall population
  • In the elderly (≥ 65 years old), the vaccine was about 86.4% effective
  • Against severe COVID-19, the vaccine was 100% effective starting 14 days after the 2nd dose
  • In the clinical trial, the vaccine was about 66.3% effective in the overall population
  • In the elderly (≥ 60 years old), the vaccine was about 76.3% effective
  • Against severe/critical COVID-19, the vaccine was about 76.7% effective 14 days after vaccination
Common adverse effects (>5%)
  • Injection site reactions (pain, redness, swelling)
  • Fatigue
  • Headache
  • Muscle pain
  • Chills
  • Joint pain
  • Fever
  • Diarrhea
  • Nausea

For the 2 vaccines that require a second dose, systemic adverse effects (fever, fatigue, headache, chills, joint/ muscle pain) are more commonly seen after the second dose is administered compared to the first dose.

Serious adverse effect*
  • Appendicitis
  • Myocardial infarction
  • Cerebrovascular accident
  • Shoulder injury
  • Ventricular arrhythmia
  • Lymphadenopathy
  • Bell’s palsy (facial paralysis)
  • Lymphadenopathy
  • Myocardial infarction
  • Cholecystitis
  • Nephrolithiasis
  • Facial swelling
  • Bell’s palsy (facial paralysis)
  • Radiculitis brachial
  • Facial paralysis
  • Guillain-Barre Syndrome
  • Pericarditis
  • Deep vein thrombosis
  • Epstein-Barr infection
  • Atrial flutter

*Only reactions that were considered possibly related to the vaccine or were more common in the vaccine group in clinical trials are listed

Can I receive a Covid-19 vaccine if I am pregnant or breastfeeding?

Any of the available COVID-19 vaccines can be offered to people who are pregnant or breastfeeding. Getting vaccinated is a personal choice, and a conversation with a healthcare provider may help with decision-making.

Pregnant women are at an increased risk for severe illness (intensive care admission, mechanical ventilation, or death) from COVID-19, and they may be at an increased risk of adverse pregnancy outcomes, such as preterm birth. Currently, there are limited data on the safety of COVID-19 vaccines in pregnant women. Animal studies found no safety concerns, and human trials evaluating the safety of the vaccines in pregnant women are underway. Despite the limited data, based on the available information, experts believe that the COVID-19 vaccines are unlikely to pose a specific risk to the mother or the fetus because these vaccines cannot cause an infection. The manufacturers are collecting and monitoring data from people in the clinical trials who became pregnant after receiving the vaccines. Additionally, the Center for Disease Control and Prevention (CDC) and the Food & Drug Administration (FDA) have safety monitoring systems in place to gather more information about vaccination during pregnancy.

The COVID-19 vaccines have not been studied in lactating people; therefore, there is no information on the effects of COVID-19 vaccines in lactating people, the breastfed infants, or whether these vaccines affect milk production or exertion. However, the FDA-authorized COVID-19 vaccines cannot cause an infection in lactating people or the breastfed infants; therefore, lactating people may decide to get vaccinated.

Should I be worried about receiving the Johnson and Johnson (Janssen) vaccine considering the recent news of blood clots?

More than 6.8 million doses of the Johnson and Johnson (Janssen) vaccine have been administered with 6 reports of a rare and severe type of blood clots (thrombosis with thrombocytopenia syndrome (TTS)). All 6 cases occurred among women between the ages of 18 and 48. The adverse events appear to be extremely rare, and the CDC and FDA still recommend the use of the Johnson and Johnson (Janssen) vaccine because the vaccine’s known and potential benefits outweigh its risks. Case reports of this adverse effect have NOT been reported with the Moderna or Pfizer-BioNTech COVID-19 vaccines.

This guide has been provided for general information purposes only and is not intended to be used as medical advice. If you have any specific questions regarding your own circumstances, please contact your health provider directly.

  1. CDC website 
  2. FDA briefing documents found on the FDA website
  3. Polack FP, Thomas SJ, Kitchin N, et al. Safety and efficacy of the BNT162b2 mRNA Covid-19 vaccine. N Engl J Med. 2020;383(27):2603-2615. doi:10.1056/ NEJMoa2034577.


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