Vaccines for COVID-19

What patients need to know about COVID-19 vaccine development efforts, the technologies being used, and how the process is being accelerated to address the unique challenges of the pandemic.

Why Vaccines for COVID-19?

The coronavirus disease 2019 (COVID-19) pandemic has brought the world to an impasse. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes COVID-19 has infected at least 75 million people and killed more than 1.6 million individuals globally.

Vaccines work by stimulating a person’s immune system to “remember” certain protein patterns of a given virus, thereby enabling that person to launch an immediate immune response against that virus if it enters their body. Importantly, vaccines not only protect you from disease but also decrease the likelihood of spreading disease to family, friends and the community at large.

Despite the promise that vaccines hold for protecting against COVID-19, physical distancing, handwashing and the use of masks remain the mainstay of prevention and protection.

How COVID-19 Vaccine Approval Timelines are Being Accelerated

Because the immune response in COVID-19 infections is poorly understood, scientists are unclear which types of vaccines will be most successful. Thus, research labs are developing many different varieties of vaccines. In an October 2020 publication of Nature Reviews Immunology, leading authors Dr. Zhou Xing and Dr. Brian Lichty charted at least 166 vaccine candidates currently in preclinical and clinical development.

Importantly, vaccines are typically developed and approved under a rigorous process with the Food and Drug Administration (FDA), lasting roughly 10-15 years. However, to meet the urgent need for a vaccine during the COVID-19 pandemic, novel vaccine development programs have been proposed that compress this extensive process into 1-2 years.

This accelerated vaccine development timeline includes the same stages as the traditional 10-15 year process; however, these stages overlap (Figure 1).

Figure 1. Timeline of vaccine development under (A) “normal” circumstances or (B) during the COVID-19 pandemic.

The above compressed timeline (Fig 1B) ensures that a vaccine can be distributed to the public ~10X faster than under normal circumstances. Critically, although vaccine candidates are propelled along the typical timeline, short-term safety considerations remain an essential component of the approval process. However, because the development time is compressed ~10-fold, information regarding long-term safety and the longevity of vaccine-induced immunity is unavailable.

For more information regarding the safety and efficacy of vaccines approved under the accelerated timeframe, see this article by a panel of medical doctors from UCSF.

What Are The Different Types of COVID-19 Vaccines?

To fight human viruses, there are many ways to classify the distinct “platforms” used to develop vaccine candidates. At Amory Medical, we have separated them into seven sub-types:

1. Live attenuated virus

2. Recombinant viral-vectored vaccines that are bioengineered to express target pathogen antigens in vivo

3. Inactivated or killed virus

4. Protein subunit vaccines

5. Virus-like particles (VLPs)

6. mRNA vaccines

7. DNA vaccines

Figure 2. Comparing development of different vaccine platforms for infectious SARS-CoV2 (coronavirus 2019).

Note: in the above image, the red text below each vaccine subtype reflects the number of COVID-19 candidate vaccines currently in clinical development for that platform.

For more detailed definitions of the different vaccine platforms and an overview of how each type works to evoke an immune response, see our Vaccines 101 blog.

Because it is difficult for researchers to know which platforms will be most successful in the fight against COVID-19, vaccine candidates are being developed across all seven of these platforms. The most common type in the COVID-19 clinical trials is protein subunit, which is a safe, well-documented platform that can simplify vaccine development and production.

However, the lead candidates currently showing the most promise for COVID-19 are messenger RNA (i.e., mRNA) vaccines, including the only two (i.e., Pfizer-BioNTech and Moderna) to receive FDA emergency use approval in the United States. Perhaps the most innovative of the vaccine platforms for COVID-19, these vaccines teach our genes how to make a piece of a protein found on the surface of the SARS-CoV-2 virus.

Each of these vaccine types offer different advantages and disadvantages across a range of factors, including:

• Safety. Could the vaccine cause the COVID-19 disease itself? Do patients experience any adverse events (i.e., possible side effects) afterwards?

• Efficacy. Does the vaccine generate a sufficient immune response to prevent COVID-19?

• Dosing. Is a repeat “booster” shot required for the vaccine to be effective?

• Adjuvant use. Does the vaccine require an additive substance to be co-injected with the antigen to trigger a strong immune response?

• Cost. Is the vaccine cost-effective to mass produce and distribute?

The below chart provides a high-level overview of the different pros and cons for each vaccine platform:

Table 1. Comparison of different vaccine platforms for COVID-19.

Note: Table 1 information sourced from: Immunological considerations for COVID-19 vaccine strategies and Recent Advances in Subunit Vaccine Carriers. Caveat: safety for use in immunocompromised patients is based on previous data from NON COVID-19 vaccines. More studies are needed to definitively determine which specific COVID-19 vaccines are safe for use in immunocompromised individuals.

When Will COVID-19 Vaccines Be Available?

Although many vaccines are being evaluated at an accelerated rate, the world is likely still in the range of years away from global mass immunization. Even if a vaccine is approved within the next several months, the initial doses will likely be reserved for “priority vaccination” of high-risk groups such as health-care workers, seniors, individuals with underlying health conditions, and ethnic minorities hit hardest by COVID-19.

Considering that long-term data on the efficacy of each vaccine cannot be available in such a short period of time, the first vaccine that is approved may not be the same vaccine that is mass distributed. Therefore, experts emphasize patience with COVID-19 vaccines and stress that initial positive reports must stand the test of time before they are hailed as a true success.

Until such a time as we have effective and safe vaccinations, prevention of infection by wearing a mask, copious handwashing, and physical distancing remain essential components of COVID-19 disease prevention.

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