An Overview of the Merck COVID-19 Vaccine

Merck, one of the largest pharmaceutical companies in the world, focused its early efforts in the fight against the coronavirus disease 2019 (COVID-19) on looking for ways to treat people who were sick. Now, the U.S. company is also working on vaccine development and has two vaccine candidates.

Both are viral vector vaccines that use modified versions of other viruses to deliver instructions to cells. The company began enrolling participants in an early-stage clinical trial for COVID-19 vaccine candidate V591 in late August and an early-stage clinical trial for candidate V590 in late September.

Merck is expected to share some preliminary results from the vaccine trials in early 2021.

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Merck KGaA / Creative Commons

How It Works

Merck's vaccine candidate V591 is a recombinant vaccine that uses a live virus (measles) vaccine as the delivery method for transporting a small piece of the coronavirus' genetic code to create an immune response. Recombinant viruses are genetically engineered viruses, which can be designed to act as vaccines when antigen genes are added.

V591 was launched by Merck with the purchase of Themis, a private company focused on immunity and vaccines that Merck acquired in June 2020.

Merck is collaborating with the International AIDS Vaccine Initiative (IAVI) on the development of its other vaccine candidate, V590. 

V590 uses recombinant vesicular stomatitis virus (rVSV) technology—the same that was used by Merck to develop a vaccine to fight the Ebola virus. For this particular vaccine, Merck is using a common animal virus that has been changed to use certain proteins on the virus that help launch an immune response to the novel coronavirus.

How Effective Is It?

There is no data available yet on how the Merck vaccines will perform. Results of early safety trials are expected in early 2021 and depending on the preliminary results, larger trials may follow.

When Will It Be Available?

Since Merck only began early clinical trials in August for one candidate and September for the other, it is difficult to say when or if its vaccines may be available. It will take at least several more months to conduct larger Phase 2/3 or Phase 3 trials and collect data on safety and efficacy for the candidates, let alone receive regulatory approval. A vaccine likely won't come from Merck until late 2021.

Who Can Get the Merck Vaccine?

Merck enrolled 260 participants 18 and older, grouping them by those 18 to 55 and those older than 55, for the V591 trial, but there is no more specific information on populations that should or should not get the vaccine. Merck's enrollment for the V590 trial is also 18 and older with similar age groupings.

If one or both of the company's vaccine candidates are authorized, the Centers for Disease Control and Prevention (CDC) is likely to dictate who should receive the vaccine and when. CDC is overseeing the distribution of vaccines to fight COVID-19 and identifying people who should be vaccinated first based on risk level. CDC’s Advisory Committee on Immunization Practices (ACIP) has made recommendations on how to prioritize vaccine supplies for COVID-19 vaccination, yet it can vary by state during distribution. 

The CDC estimated that it will take several months before the supply of vaccines catches up to the demand. Guidance on who will receive the vaccine and when will be decided as supplies become available. The United States alone has a population of about 330 million—meaning nearly 700 million vaccine doses will be needed to vaccinate all of America if other vaccines follow a two-vaccine dose.

Although little information is available on the specifics of when everyone will receive the vaccines against COVID-19 and where they can get it, state and local health departments will be coordinating efforts to distribute doses of the vaccines as they become available. The vaccines should be available both in physician offices and retail locations like pharmacies that administer other vaccines.

As vaccines become available, any doses purchased by the U.S. government will be free to its citizens, according to CDC. While the vaccine itself is free, the facility or agency that offers the vaccine may charge a fee for administration. Public health programs and insurance plans are expected to reimburse patients for any costs associated with COVID-19 vaccination, but not much information has been made available yet.

Side Effects and Adverse Events

The Merck studies are not far enough along to provide information on adverse events or side effects associated with the vaccines.

Funding and Development

Merck has received more than $38 million in funding from the U.S. government for its COVID-19 vaccine program as part of Operation Warp Speed, a public-private partnership initiated by the U.S. government to facilitate and accelerate the development of a COVID-19 vaccine, and from the Biomedical Advanced Research and Development Authority (BARDA).

BARDA is a program that falls under the U.S. Department of Health and Human Services. That program and Operation Warp Speed have sought to speed up how quickly vaccines to fight COVID-19 can be developed and approved for use.

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Article Sources
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  1. World Health Organization. Draft landscape of COVID-19 candidates. Updated January 12, 2021.

  2. Merck. IAVI and Merck collaborate to develop vaccine against SARS-CoV-2. Updated May 26, 2020.

  3. National Institutes of Health. A study to assess safety, tolerability, and immunogenicity of V591 (COVID-19 vaccine) in healthy participants (V591-001). Updated December 7, 2020.

  4. Centers for Disease Control and Prevention. 8 things to know about the U.S. COVID-19 vaccination program. Updated December 18, 2020.

  5. U.S. Department of Health and Human Services. BARDA’s rapidly expanding COVID-19 medical countermeasure portfolio.