Vaccine Development

Vaccine Development During COVID-19 Year One

(Links verified on February 13, 2025)

The immune system mounts a response when it encounters a viral infection, producing antibodies that protect against future infections by the same virus. A vaccine is designed to trigger this immune response so that the body produces these protective antibodies without ever experiencing the actual infection.

The traditional method for producing a vaccine against a virus involves weakening, killing, or otherwise inactivating the virus so that it cannot replicate. The immune system generates antibodies based on the virus’s molecular structure, so if that structure remains essentially unchanged during the inactivation process, the vaccine will trigger an immune response similar to that elicited by a live virus. The Chinese Sinovac “CoronaVac” COVID-19 vaccine is an example of an nactivated virus vaccine.

A novel approach to vaccine development involves incorporating only the specific parts of the virus that trigger the strongest immune response. For SARS-CoV-2, that key component is the spike protein, which acts as the antigen responsible for stimulating the immune system. The U.S.-based Novavax “NVX-CoV2373” COVID-19 vaccine, still in development, is an example of a protein subunit vaccine that employs this strategy.

Another modern method for developing vaccines is to deliver genetic material—either RNA or DNA—into the body, prompting human cells to produce a viral protein. Living cells continuously express the proteins they need according to the instructions encoded in their own DNA and RNA. When a vaccine contains RNA that encodes the spike protein, the cell’s machinery translates that RNA into the spike protein, which then serves as an antigen to trigger the desired immune response. This is the principle behind COVID-19 mRNA vaccines such as the Pfizer/BioNTech and Moderna vaccines. For a more detailed explanation, see How mRNA vaccines work or How mRNA vaccines work (Easy).

Another modern approach to vaccine development involves re-engineering a harmless virus, such as an adenovirus, so that it is unable to replicate and is modified to carry the DNA sequence that encodes the spike protein. When this adenoviral vector is administered as a vaccine, it delivers the genetic material into human cells, which then produce the spike protein, triggering an immune response. This is the principle behind adenoviral vector vaccines, such as the AstraZeneca/Oxford and Johnson & Johnson/Janssen COVID-19 vaccines.

Since early 2020, nearly all global COVID-19 vaccine development efforts have focused on introducing genetic material—either RNA or DNA—into the human body to prompt human cells to produce antigens that mimic key components of SARS-CoV-2, such as the spike or capsid proteins.

Types of vaccine:

  • 1) Inactivated virus vaccine
    • This is a traditionally developed vaccine that uses viruses which have been inactivated (killed) through chemical or heat treatment, so they cannot replicate. These vaccines may contain whole, dead viruses or fragments of the virus, which stimulate an immune response without causing disease.
  • 2) mRNA vaccine
    • Mechanism:
      • It contains messenger RNA (mRNA) that encodes the spike protein antigen. Once administered, the mRNA instructs the body’s cells to produce the spike protein, thereby triggering an immune response.
    • Current Use:
      • This technology is employed in the Pfizer/BioNTech and Moderna COVID-19 vaccines.
    • Disadvantages:
      • One disadvantage is that mRNA is less stable and prone to degradation, requiring storage at refrigerated or frozen temperatures. Additionally, scaling up the manufacturing process for these vaccines presents significant challenges.
    • Read How mRNA vaccines work or How mRNA vaccines work (Easy).
  • 3) Adenoviral vector vaccine
    • Mechanism:
      • This vaccine uses an adenovirus—a type of common cold virus—that has been genetically modified to carry DNA encoding the spike protein antigen. When administered, the engineered adenovirus delivers this DNA into human cells, which then produce the spike protein to stimulate an immune response.
    • Current Use:
      • Adenoviral vector vaccines are currently in use against COVID-19, including those developed by AstraZeneca/Oxford and Johnson & Johnson/Janssen.
    • Vaccine Design Feature:
      • The adenovirus is engineered so that it cannot replicate within the body, enhancing its safety profile.
    • Advantages:
      • This platform is relatively easy to scale up for mass production of vaccines.
    • Disadvantages:
      • However, the development process for these vaccines may take longer compared to some other vaccine technologies.
  • 4) Protein subunit vaccine
    • Mechanism:
      • This type of vaccine contains purified spike proteins from the virus. These proteins act as antigens, triggering an immune response without the need for live or inactivated viruses.
    • Example:
      • The Novavax COVID-19 vaccine (NVX-CoV2373) is an example of a protein subunit vaccine.
  • 5) DNA vaccine
    • Contain DNA plasmids (circular DNA fragments) designed to express viral antigens.
    • Disadvantages:
      • More difficult to scale up for mass production compared to other vaccine types.
      • Potential concerns about DNA integration, as these vaccines require entry into the cell nucleus.
      • No DNA-based COVID-19 vaccines have been widely deployed.

Mayo Clinic: Different types of COVID-19 vaccines: How they work



Vaccines currently in use (by March 24, 2021)

Developer: Pfizer/BioNTech
Name: BNT162/Comirnaty
Developed in: USA/Germany
Type: mRNA vaccine
Approval: USA Emergency Use (EUA) on December 11, 2020; WHO Emergency Use Listing (EUL) on December 31, 2020; …
Doses: 2
Interval between doses: 21 days
FDA: Pfizer-BioNTech COVID-19 Vaccine

Developer: Moderna
Name: mRNA-1273
Developed in: USA
Type: mRNA vaccine
Approval: USA EUA on December 18, 2020; …
Doses: 2
Interval between doses: 28 days
FDA: Moderna COVID-19 Vaccine (page moved or removed)
Moderna: White paper (PDF) (moved or removed)
Moderna website

Developer: AstraZeneca/Oxford
Name: ChAdOx1 (manufactured by Serum Institute of India as Covishield)
Developed in: United Kingdom
Type: Adenoviral vector
Approval: UK Emergency Use on December 30, 2020; WHO EUL on February 15, 2021; …
Doses: 2
Interval between doses: 28 to 84 days
GOV.UK: Information for UK recipients on COVID 19 Vaccine AstraZeneca

Developer: Johnson & Johnson/Janssen
Name: AD26.COV2.S
Developed in: USA/Belgium
Type: Adenoviral vector
Approval: USA EUA on February 27, 2021; WHO EUL on March 12, 2021; …
Doses: 1
FDA: Janssen COVID-19 Vaccine
J&J: Simplifying the Science of COVID-19: How Adenovector Vaccines Work (VIDEO)

Developer: Sinovac Biotech Ltd.
Name: Coronavac
Developed in: China
Type: Inactivated virus
Approval: China on February 6, 2021; …
Doses: 2
Interval between doses: 14 days

Developer: Gamaleya Institute
Name: Sputnik V
Developed in: Russia
Type: Adenoviral vector
Approval: Russia on August 11, 2020; Philippines EUA on March 19, 2021; …
Doses: 2
Interval between doses: 21 days
Official site

Developer: CanSino
Name: Ad5-nCov
Developed in: China
Type: Adenoviral vector
Approval: China Marketing Authorization (for Convidecia) on February 25, 2021; Hungary EUA on March 22 2021; …
Doses: 1
CanSinoBIO website

Developer: Bharat Biotech
Name: Covaxin
Developed in: India
Type: Inactivated virus
Approval: India EUA on January 3, 2021; …
Doses: 2
Interval between doses: 14 days

Developer: Anhui Zhifei Longcom
Name: RBD-Dimer
Developed in: China
Type: Protein subunit
Approval: China on March 16, 2021; …
Doses: 3
Interval between doses: 1 month

Developer: FBRI
Name: EpiVacCorona
Developed in: Russia
Type: Protein subunit
Approval Russia on October 14, 2020; …
Approval: Russia

Developer: Sinopharm (Beijing)
Name: BBIBP-CorV
Developed in: China
Type: Inactivated virus
Approval: China
Doses: 2

Developer: Sinopharm (Wuhan)
Name: Inactivated (Vero Cell)
Developed in: China
Type: Inactivated virus
Approval: China
Doses: 2

Some vaccines still in development

Developer: Novavax
Name: NVX-CoV2373
Developed in: USA
Type: Protein subunit
Approval: Possibly in May, 2021
Doses: 2
Interval between doses: 21 days
Press release (page moved or removed)

…


General information on Covid-19 vaccines

WHO: Covid-19 vaccines (moved or removed)

Status of Covid-19 vaccines within EUL/PQ evaluation … (PDF)
(March 23, 2021)

vfa: Vaccines to protect against Covid-19… (February 1, 2021)

NatGeo: Here’s the latest on COVID-19 vaccines (March 24, 2021)

Google search for the latest vaccine tables



Vaccine trackers and guides

STAT Covid-19 Drugs and Vaccines Tracker with a vaccine research chart.

Covid-19 Vaccine Tracker

NYT: Coronavirus Vaccine Tracker

The race for coronavirus vaccines: a graphical guide

Reuters: Factbox – When and which COVID-19 vaccines are likely to be available in Asia

CDC: Comparing the Covid-19 vaccines developed by Pfizer, Moderna, and Johnson & Johnson (February 2, 2021) (page moved or removed)


Vaccine development on the Timeline

For more information on vaccines on this site, go to the Vaccine development (Timeline) page to learn how vaccine development has proceeded since early 2020.

©2020, 2021 Dr. Michael Herrera