Which candidate is winning in the race to develop a vaccine against the novel coronavirus SARS-CoV-2? It depends on whom you ask.

World Health Organization (WHO) chief scientist Soumya Swaminathan said several weeks ago that an experimental COVID-19 vaccine being developed by AstraZeneca and the University of Oxford was "probably the leading candidate." But President Donald Trump appears to have a different view.

On Wednesday, the president stated: "We think we have a winner." He was referring to the COVID-19 vaccine candidate being developed by Pfizer (PFE -0.04%) and German biotech BioNTech (BNTX -1.95%). Why is President Trump optimistic about the experimental vaccine?

President Trump speaking at the White House

Image source: WhiteHouse.gov.

Encouraging results

The president's comments came just two days after Pfizer and BioNTech announced encouraging results from a phase 1/2 study of BNT162b1 underway in Germany. The experimental vaccine is one of four coronavirus vaccine candidates the companies are jointly developing.

BNT162b1 produced high levels of neutralizing antibodies and T-cell responses in study participants receiving two doses of the experimental vaccine. Neutralizing antibodies and T-cell responses hold the potential to prevent infection by the novel coronavirus.

In addition, Pfizer and BioNTech said that BNT162b1 had "a manageable tolerability profile." There weren't any serious adverse events reported in the clinical study. However, some participants experienced injection-site reactions and had flu-like symptoms.

These results matched up well with data from a U.S. phase 1/2 clinical study reported earlier this month. However, the earlier results didn't include the T-cell response observed in the German clinical trial.

Big money

Hours before President Trump lauded Pfizer's and BioNTech's COVID-19 vaccine candidate, the U.S. government put a lot of money on the line with the experimental vaccine. The U.S. Department of Health and Human Services and the Department of Defense agreed to pay $1.95 billion for 100 million doses of BNT162.

No money has exchanged hands yet, though. The payment will be made after the U.S. government receives the 100 million doses. That can't happen until the Food and Drug Administration either approves the vaccine or grants emergency-use authorization.

This could be just the beginning of a lucrative deal for Pfizer and BioNTech. As part of the agreement, the U.S. government can buy up to 500 million additional doses of the COVID-19 vaccine.

Earlier last week, Pfizer and BioNTech signed a smaller agreement with the United Kingdom. The companies will supply 30 million doses of their COVID-19 candidate, pending successful late-stage testing and regulatory approval. However, no financial details were disclosed.

A winner?

Pfizer and BioNTech expect to begin a phase 2b/3 study very soon, perhaps by the end of July. If all goes well, they anticipate seeking regulatory approvals as early as October.

Investors hoping to become winners from the COVID-19 vaccine race could find both Pfizer and BioNTech stocks appealing. The U.S. government deal alone holds the potential for nearly $12 billion in sales if the option to buy an additional 500 million doses is exercised.

More conservative investors will probably prefer Pfizer. The big drugmaker has a long lineup of approved products already, and wouldn't be hurt as much if the BNT162 program isn't successful in late-stage testing. Aggressive investors would probably find BioNTech more to their liking. With a market cap of less than $20 billion, the biotech stock should have plenty of room to run if BNT162 lives up to its potential.

Pfizer and BioNTech aren't your only choices when it comes to possible COVID-19 vaccine winners, though. As President Trump stated on Wednesday, "We also think we have other companies right behind that are doing very well on the vaccines, long ahead of schedule."

He's right that there are other drugmakers with promising coronavirus vaccine candidates. Some of them aren't "right behind" Pfizer and BioNTech; they're actually ahead of the two companies in terms of clinical progress.

Pfizer's and BioNTech's vaccine candidate could very well be the winner that the president thinks it will be. But it won't necessarily be the only winner.