Pfizer (PFE 0.89%) and its German partner BioNTech (BNTX 5.55%) reported incredible efficacy data from a phase 3 trial for their mRNA coronavirus vaccine candidate last Monday. While the 90% figure inspired much hope, investors should know this was interim data that have not yet been peer-reviewed. This week, Moderna (MRNA 11.65%) reported equally impressive results for its vaccine candidate that takes a similar approach.

We spoke with Dr. Angela Rasmussen, a virologist and Associate Research Scientist at Columbia Center for Infection and Immunity, about one of the companies working on a COVID-19 vaccine that hasn't been hogging the headlines: GlaxoSmithKline (GSK 0.38%).

Corinne Cardina: David Applebee asked, "What is the category of COVID-19 vaccine that GlaxoSmithKline and Sanofi (SNY 1.38%) are developing?" I love this tracker that I'm putting in the chat. It's by BioPharmaDive. It goes through all of the candidates in late-stage trials, tells you exactly what mechanism they are taking, so give that a look. I believe it says that GlaxoSmithKline is using the protein. Let me just search here. Dr. Angela, are you familiar with the GlaxoSmithKline candidate?

Rasmussen: There are so many of them that I'm looking at the tracker right now to remind myself because I don't want to say the wrong thing.

Cardina: No problem. It's protein-based. It says, "coronavirus-derived protein produced in insect cell lines." Like what Dr. Angela was talking about with the chicken eggs, this uses insect cells extracted and delivered alongside an adjuvant. So take a look at that.

Rasmussen: I can tell you based on that description what it is. It's what's called a subunit vaccine. It's a little different than the influenza vaccine. This doesn't actually require them to grow up the virus either. This is using an insect cell expression system. Novavax (NVAX 10.86%) is another example of a vaccine that is being produced in this way; to grow up what I'm sure is probably the spike protein and possibly one or two other proteins, I'm not sure. Coronavirus-derived protein usually means spike, but it can also mean nucleic acid and envelope proteins as well. But in any case, they're growing up protein antigen in these insect cells, and then they're giving you that protein antigen with an additional adjuvant which is something that stimulates the immune system further because proteins alone often are not very immunogenic or capable of eliciting robust immune responses. So these types of vaccines are also usually given with some type of adjuvant. Another example of a vaccine like this would be the hepatitis B vaccine which is also a subunit vaccine. I don't believe it has an adjuvant but they usually give three doses of that vaccine to make up for the fact that it does not.