How Do COVID-19 Vaccines Work?

More than 150 vaccine candidates against the COVID-19 coronavirus pandemic are in various stages of development. One from Pfizer-BioNTech was cleared for emergency use in the US in mid-December 2020.

The COVID-19 pandemic caused by the SARS-CoV-2 coronavirus has afflicted millions of people worldwide. This global crisis has spurred dozens of vaccine development efforts by drug companies, universities and governments. 

Around 150 vaccines were in various stages of development across the globe as of mid December 2020; many had completed the Phase III clinical trials, a final step leading to approval by governments around the world. 

These vaccines will hit the market once the United States Food and Drug Administration (U.S. FDA) confirms their effectiveness and safety.

Full approval is not necessary to start distributing promising vaccines; the FDA has granted the Pfizer-BioNTech vaccine an emergency use authorization (EUA). The first doses of this vaccine for vaccinating individuals aged 16 years and above began US distribution in mid-December 2020, and the following vaccines were expected to soon follow:

• Moderna’s COVID-19 vaccine
• AstraZeneca’s COVID-19 vaccine
• Janssen’s COVID-19 vaccine
• Novavax’s COVID-19 vaccine

The COVID-19 vaccine helps your body fight the virus by training and tempering the immune system, strengthening your own biological defenses to repel the viral invaders in case you are exposed accidentally. 

These are called immune responses to vaccination and are as follows: 

• The white blood cells type-T (T cells) identify and kill the virus (cellular immunity).
• The white blood cells type-B (B cells) make antibodies (proteins) to neutralize the virus.

The vaccine trains your white blood cells to recognize the virus well before it starts multiplying inside your body. It also teaches both the T and B cells to retain infection memory, providing a lasting immunity.

As more and more people get vaccinated, the rate of active infections will shrink, leading to fewer infected people shedding virus in each community. This will help protect even those people who are yet to be vaccinated, a concept called herd immunity.

Herd immunity may develop without a vaccine as a critical mass of people are infected through community spread of the virus. They either clear the virus or die, slowly increasing a group’s overall immunity to infection until the virus stops spreading altogether. 

This scenario costs many more lives than artificially inducing herd immunity through mass vaccination. Most health authorities around the globe endorse some combination of social distancing, masking and mass-vaccination to reduce the number of new infections.

The various types of COVID-19 vaccines in development are as follows:

• Inactivated virus vaccine: In this technique, the vaccine is manufactured using an inactivated or weakened virus. This weak virus does not cause disease, but it is sufficient to generate an immune response.
• Live attenuated viruses: A genetically weakened (harmless) version of the COVID-19 virus is manufactured inside a lab to make the vaccine. A healthy body generates an immune response to the weak virus. In the process, the white blood cells memorize the viral structure, allowing your body to mount a stronger immune response in the event you are exposed to the actual infection.
• Vaccines using the recombinant proteins: These vaccines use a protein shell that mimics the COVID-19 viral structure. Immune response mounted against this shell works against the live COVID-19 virus, too.
• Vaccines using vectors: Vector vaccines use a common cold virus as a vector (carrier). The code for a COVID-19-specific protein is inserted inside this virus. Once the vector is inside our cells; it releases the “code” inside our body. This code guides our cells to make the COVID-19-specific protein, triggering a strong immune response by white cells.
• DNA vaccines: This vaccine uses a lab grown bacteria to produce genetically engineered DNA that codes for a spike protein. This protein is specific to the COVID-19 virus. When injected, our cells read the DNA template for spike protein, inducing mass production of the protein. The protein sparks an immune response via white cells, preparing them to fight off a coronavirus infection.
• mRNA vaccines: This is a cutting-edge technique using a genetically engineered messenger RNA (mRNA that takes the message from the DNA to the protein-making machinery in the cell) that codes for the COVID-19 specific protein. When injected, this mRNA provides our cells instructions to make the COVID-19 specific protein, which in turn makes the white cells mount an immune response. The Pfizer-BioNTech vaccine uses this technology.

Most of the COVID-19 vaccines consist of two shots given intramuscularly. The first shot is to start building protection. A second shot boosts the level of the protection. As of mid-December 2020, it was unclear how long the immunity conferred by the vaccines will last. 

Further adding to logistical challenges in distributing millions of doses, all the vaccines are temperature-sensitive, and maintaining a proper storage is extremely important to maintain their potency. Refrigerated transport and storage is necessary at all levels of the supply chain.

The following vaccines are in final stages of development and will hit the market in early 2021. Other contenders in Stage II will be out in the latter half of 2021. Those are not mentioned in this list.

NOTE: Efficacy, in this table, is calculated as preventing symptomatic COVID-19 after the second dose

As the research evolves, we will be able to make informed decisions about which vaccine is best suited for each country and region’s climate, viral strains and particular public health challenges. 

Until then, hand washing, social distancing, and masks are the greatest protection against the virus.

Four cases of Bell’s palsy were reported among the Pfizer and BioNTech vaccine study in mid December 2020, according to the Food and Drug Administration (FDA). All four cases were in the group that received the vaccine and not the placebo, though that number of cases is not more than would be expected in the general population. 

The FDA is monitoring vaccine recipients for evidence of new cases of Bell’s palsy.