What are the current leading candidates for a COVID-19 vaccine?

While there hasn’t yet been an approved vaccine for COVID-19, many different types of vaccines are in development. We break down the types of vaccines and how each works.

Messenger RNA (mRNA) vaccines

The two leading vaccine candidates (made by Pfizer, in whose clinical trial we are participating, and Moderna) are mRNA vaccines. mRNA is the genetic instruction manual that cells use to make proteins.

These injected vaccines deliver mRNA instructions for the coronavirus spike protein into our body. Our cells use the instructions to manufacture spike proteins and display them to the immune system in a way that looks like an actual infection. The immune system responds and creates antibodies and other immune cells that recognize the spike protein.

The early results from the vaccine studies show the vaccines are stimulating an antibody response that’s actually stronger than the antibody response from having COVID, even though neither contains actual virus. mRNA vaccines can be quickly designed and manufactured.

Within the space of a week in mid-November, both mRNA vaccine trials announced very encouraging results.

On Nov. 18, Pfizer and their partner BioNTech announced interim results from their clinical trial indicating that the vaccine may be more than 95% effective at preventing COVID-19.

When half of the study’s more than 40,000 participants have been followed for safety issues for at least two months after their second dose of the vaccine, a milestone the company expected to hit by the third week of November, Pfizer present the data to the FDA on Nov. 20 and requested emergency use authorization to use the vaccine.

UI Health Care was a study site for the Pfizer vaccine trial and was directly involved in collecting some of the data that went into this recent announcement, having enrolled about 270 diverse individuals in the trial.

And on Nov. 16, Moderna made a similarly promising announcement regarding the efficacy of their mRNA vaccine. Based on interim findings from their 30,000-patient clinical trial, they found the vaccine was 94.5% effective in preventing COVID-19.

Viral-vector vaccines (e.g., AstraZeneca, Johnson and Johnson)

A harmless virus that cannot cause infection is used as a vector to transport genes for coronavirus proteins, like the spike protein, into cells. Some of these viruses are replicating vectors that can reproduce inside cells and make more “vaccine” inside your body.

These vaccines can be designed and created fast. A possible problem is that the body can create an immune response to the vector, which then hinders a booster dose, because the vaccine itself gets cleared by the immune system before it can enter cells.

On Monday, Nov. 23, AstraZeneca announced its vaccine has shown to be, on average, 70% effective in large-scale trials.

Subunit vaccines (e.g., Novavax)

In these vaccines’ viral proteins, like the spike protein, are delivered naked or inside a virus-like particle to the body. The proteins enter a certain type of immune cell in a person’s body and get displayed to the rest of the immune system in a way that looks like an infection (although it is not), which provokes the antibody response.

UI Health Care is currently participating in the Novavax clinical trial.

Weakened or inactivated (killed) virus

A more traditional vaccine technology (it is used to make the Polio vaccine, for example), this uses actual virus but in a weakened or dead form that cannot cause disease. The immune system doesn’t care that the vaccine is disabled, it still reacts as if it were a real infection and produces the immune response, including antibodies (and T-cells)

This type of vaccine takes longer to make and there are no COVID vaccines in pursuit using this technology.