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Covid Vaccine Update and FAQs

By Craig P. Tanio, MD, FACP, IFMCP

Covid-19 Vaccines

Given the rapidly moving developments we have put together a FAQ on the Covid-19 Vaccines. This is up to date as of December 16th and we will update it as needed.

What vaccines are starting to become available?

  • Pfizer / BioNTech mRNA vaccine was received emergency use authorization by the FDA last week and the first doses were given on December 14th. Moderna also has a mRNA vaccine which is being evaluated for emergency use authorization by the FDA with a decision expected before the end of December. 
  • Messenger RNA vaccines include mRNA (wrapped in a lipid nanoparticle) that gets incorporated into human cells upon vaccination. This mRNA encodes for the viral spike protein in Covid-19. The mRNA instructs the host cell to produce the spike protein, which stimulates an immune response that will ultimately provide protection against Covid-19. This is the first mRNA vaccine to be rolled out.
  • The Oxford / AstraZeneca vector vaccine has published Phase 3 evaluation data with the first dose given to a UK patient as part of a vaccination campaign on December 2nd.  
  • Vector vaccines use a separate viral vector that has been engineered to code for proteins from the Covid-19 virus. Two of the vaccines in phase 3 trials use a replication-defective adenovirus vector that has been altered to code for the spike protein. Once the vector infects the host cell, its DNA enters the host cell nucleus. The host then produces the protein from SARS-CoV-2 which elicits and immune response and protection against COVID-19. Note that the adenovirus does not modify the host genome. There have been other vector vaccines approved for use in humans.
  • Note that no vaccines currently use live, attenuated COVID-19 virus.  

How is the Pfizer-BioNTech vaccine given?

  • 2-dose series administered IM 3 weeks apart
  • Administration of 2nd dose within 4-day grace period considered valid (day 17-21)
  • If >21 days since 1st dose, 2nd dose should be administered at earlies opportunity (but no doses need to be repeated)
  • Both doses are necessary for protection; efficacy of a single dose has not been systematically evaluated
  • COVID-19 vaccine not interchangeable with other COVID-19 vaccine products

How effective is the Pfizer vaccine?

The efficacy is 95% based on the Phase 3 data. A summary table from the NEJM article in is below:  

  • The Phase 2/3 clinical trials demonstrate similar safety and efficacy profiles in persons with underlying medical conditions, including those that place them at increased risk for severe COVID-19, compared to persons without comorbidities. Vaccine may be administered to persons with underlying medical conditions who have no contraindications to vaccination

What does the safety data show?

  • The CDC’s current position for immunocompromised patients is that:
    • data is not current available to establish the safety and efficacy of patients of the vaccine in patients with immunocompromised conditions
    • there is a potential for reduced immune responses
    • need to continue to follow all current guidance to protect themselves against transmission of Covid-19
  • Current contraindications and precautions for the Pfizer-BioNTech vaccine due to reports of anaphylactic reactions for patients vaccinated outside of trials are
    • Severe allergic reaction to any component of the Pfizer-BioNTech Covid-10 vaccine is a contraindication
    • Persons who have had a severe allergic reaction to any vaccine or injectable (IM, IV or SQ) should not receive the vaccine at this time
    • Rezilir would expand the above contraindications to include any persons who have a severe reaction to vaccines; this would include patients with Guillain-Barre syndrome who have had a rare neurological reaction to either influenza or the vaccine for influenza
  • The Pfizer safety data shows that there serious adverse events in 0.6% of patients compared to 0.5% of patients with placebo.
  • How do the side effects compare to other vaccines? Dr. Jesse O’Shea an infectious disease specialists has put together a good summary.


Polack FP and others Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine NEJM December 10, 2020

José R. Romero, & Henry H. Bernstein. COVID-19 Vaccines: A Primer for Clinicians. Pediatric Annals. 2020;49(12):e532-e536

Giurgea LT, Memoli MJ. Navigating the Quagmire: Comparison and Interpretation of COVID-19 Vaccine Phase 1/2 Clinical Trials. Vaccines (Basel). 2020 Dec 9;8(4):E746.  PMID: 33316990   

CDC COVID-19 Vaccines work group


**Disclaimer: This article is provided for informational purposes only and does not constitute endorsement of treatments, individuals, or programs which appear herein. 

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