It's difficult if not impossible to accurately assess which novel coronavirus vaccine candidates in clinical testing are likely to be the safest and most effective. For the most part, all we have to go on at this point are preliminary results from early-stage clinical studies. While several candidates appear to be promising, it's still too soon to know just how well they'll work in larger phase 3 trials.

However, there is one way to compare the vaccine candidates that's much more concrete: Look at how much money they've attracted in development funding and supply agreements. Here are the COVID-19 vaccine makers that are winning the money game so far, with more than $1 billion in funding lined up.

$100 bills falling from the sky, each with a surgical mask on Ben Franklin's face

Image source: Getty Images.

1. Sanofi/GlaxoSmithKline

Sanofi (NASDAQ:SNY) and GlaxoSmithKline (NYSE:GSK) take the top honors. Just last week, the two drugmakers announced that the U.S. government will provide funds of up to $2.1 billion for developing their protein-based, adjuvanted coronavirus vaccine candidate. Sanofi and GSK will provide 100 million doses initially, assuming all goes well in clinical testing.

What's really surprising about Sanofi and GSK ranking No. 1 is that their COVID-19 vaccine candidate hasn't even begun a clinical trial yet. Sanofi is taking the lead role in developing the experimental vaccine. The big drugmaker hopes to start a phase 1/2 study in September.

The U.S. deal could become a larger one in the future, with the option for the U.S. to buy an additional 500 million doses of the Sanofi/GSK vaccine. Sanofi and GSK are also in talks with the European Commission and the governments of other countries about potentially supplying COVID-19 vaccine doses.

2. Novavax

Novavax (NASDAQ:NVAX) ranks No. 2 in terms of funding among all drugmakers developing COVID-19 vaccine candidates. So far, the clinical-stage biotech has received commitments of nearly $2.05 billion for its coronavirus vaccine candidate, NVX-CoV2373.

Novavax first received $4 million in March from the Coalition for Epidemic Preparedness Innovations (CEPI) to support early-stage testing of the company's COVID-19 vaccine candidate. In May, CEPI upped its funding commitment to $388 million. This additional cash assisted Novavax's phase 2 development of NVX-CoV2373. It also helped the biotech scale up its manufacturing of the vaccine and increase the production of its Matrix-M adjuvant.

In June, the U.S. Department of Defense awarded Novavax a $60 million contract, with the company agreeing to supply 10 million doses of NVX-CoV2373 to the military if the vaccine received Emergency Use Authorization (EUA) from the Food and Drug Administration. But the really big prize came in July, when the U.S. government's Operation Warp Speed awarded $1.6 billion to Novavax to complete late-stage development of its COVID-19 vaccine candidate, expand its manufacturing capacity, and supply 100 million doses of NVX-CoV2373 to the United States.

3. Pfizer/BioNTech

Pfizer (NYSE:PFE) and BioNTech (NASDAQ:BNTX) come in close behind Novavax. The two partners have scored at least $1.95 billion from a supply deal with the U.S. government.

On July 22, Pfizer and BioNTech announced a deal with the U.S. Department of Health and Human Services (HHS) and the U.S. Department of Defense. In exchange for $1.95 billion, the two companies agreed to supply 100 million doses of the lead COVID-19 vaccine candidate developed in the companies' BNT162 program (pending FDA approval or an EUA). The agreement also gives the U.S. government an option to buy another 500 million doses of the vaccine.

Pfizer and BioNTech arguably deserve a higher spot. The two partners also secured a supply deal in July with the United Kingdom to supply 30 million doses of their COVID-19 vaccine candidate. However, the financial terms of this agreement weren't announced.

4. AstraZeneca

AstraZeneca (NYSE:AZN) runs neck-and-neck with Pfizer and BioNTech in the coronavirus-vaccine money game. The British drugmaker has hauled in funding of at least $1.95 billion so far for AZD1222, the COVID-19 vaccine candidate that it teamed up with the University of Oxford to develop.

Much of this amount came from a $1.2 billion commitment from the Biomedical Advanced Research and Development Authority (BARDA) in May. The funds will help AstraZeneca advance clinical studies of AZD1222 and scale up manufacturing for the vaccine. AstraZeneca agreed to supply at least 300 million doses to the U.S., assuming the vaccine wins FDA approval or EUA.

AstraZeneca also signed a $750 million deal with CEPI and public-private health partnership Gavi in June. These funds went toward supporting the manufacturing and distribution of 300 million doses of AZD1222.

Like Pfizer and BioNTech, AstraZeneca could easily rank higher on the list. However, the financial terms of its other supply deals, with the Serum Institute of India and Europe's Inclusive Vaccines Alliance, weren't disclosed.

Honorable mention

There's also a drugmaker that deserves an honorable mention. Moderna (NASDAQ:MRNA) has received as much as $955 million in funding from BARDA to support the development of its COVID-19 vaccine candidate mRNA-1273.

In terms of stock performance so far this year, though, Moderna is well ahead of all of the other big drugmakers winning the COVID-19 vaccine money game: The biotech stock is up more than 300%. However, that's still way behind Novavax's year-to-date gain of close to 3,500%.