How many vaccines are being tested in people?

There are currently three COVID-19 vaccines in Phase III (human) trials in the US, and one more starting soon. Two of the active trials are of mRNA vaccines.

How do mRNA vaccines work?

There are currently two messenger RNA (mRNA) COVID-19 vaccine trials ongoing in the US. The mRNA provides a blueprint for the “spike” protein, a component of the virus that causes COVID. Your body follows the blueprint and makes a safe fragment of the virus. Your  immune system then recognizes the fragment as an invader (even though it’s not). This stimulates a strong immune response; the body produces antibodies ready to fight the virus in case you get exposed to the real thing. 

How does the Moderna candidate vaccine work?

The first mRNA vaccine for COVID-19 was developed by Moderna with the NIH. Eventually 30,000 healthy people will be enrolled in this randomized clinical trial. Half will be randomly assigned to receive the active vaccine. This is a double blinded trial, which means the investigators will not know who received the vaccine (or a placebo). The Moderna vaccine requires two separate injections, one month apart.

This candidate vaccine has previously shown promising results in non-human primates. An initial animal study showed the vaccine stimulated neutralizing antibody activity and limited lung inflammation. A major concern, though, is that Moderna may have a difficult time quickly producing enough vaccines should the trial prove successful. The company  has never brought a vaccine to market. And the vaccine poses additional challenges to produce and distribute because it must be stored at very cold temperatures

How does the BioNTech / Pfizer candidate vaccine work?

The German company BioNTech, Chinese drugmaker Fosun Pharma, and Pfizer also have a Phase III trial of another mRNA vaccine currently underway in the US. It also has recruited approximately 30,000 participants and is a randomized, double blinded clinical trial. Phase I results showed positive neutralizing action at different dosing levels. But there were higher rates of mild adverse reactions at the highest dose. This vaccine will also be a two-dose regimen and the trial will be conducted in the US and other countries with higher rates of COVID-19 infections including Brazil, Argentina, and Germany. If approved, Pfizer plans to manufacture over 1.3 billion doses by the end of 2021.


Last update: Aug 11, 2020 01:00 pm ET

Science review: JAB, ERS