White House press secretary Kayleigh McEnany tweeted on Saturday that President Trump would hold a news conference on Sunday evening related to a "major therapeutic breakthrough" in treating COVID-19. Only hours before that news conference, the U.S. Food and Drug Administration (FDA) issued an emergency use authorization (EUA) for convalescent plasma in treating the novel coronavirus disease.

In his comments during the Sunday news conference, President Trump stated that convalescent plasma "is a powerful therapy" and said that "it's had an incredible rate of success." Here are the key things you need to know about this coronavirus therapy heralded by the president.

President Trump behind a podium at a news conference.

Image source: WhiteHouse.gov. 

What is convalescent plasma?

Plasma is a clear, yellowish liquid that makes up over half of your blood. It contains water, salts, enzymes, and -- most importantly for medical treatment -- antibodies. Convalescent plasma comes from patients who have recovered from a disease.

Patients who are infected by the novel coronavirus that causes COVID-19 develop antibodies to fight the viral disease. These antibodies float in the plasma in their blood. Physicians can harvest this plasma and isolate its antibodies to inject into other sick patients who have COVID-19. The idea is that the antibodies from the convalescent plasma can help fight the novel coronavirus infection until the patient's immune system produces enough of its own antibodies to fight the virus.

Why the FDA issued EUA

The FDA stated that it granted EUA to convalescent plasma after concluding that it "may be effective in treating COVID-19 and that the known and potential benefits of the product outweigh the known and potential risks of the product." This decision was "based on scientific evidence available," according to the agency.

It's important to note that EUA isn't the same thing as FDA approval of a therapy. The FDA stated that the EUA for convalescent plasma in treating COVID-19 could be "revised or revoked" in the future. This happened earlier this year when the agency revoked a previously issued EUA for chloroquine and hydroxychloroquine after determining that the drugs were "unlikely to be effective in treating COVID-19." 

Is convalescent plasma a breakthrough in treating COVID-19?

It's too early to know. Convalescent plasma has been used for a long time in treating other diseases with positive results. There have also been some encouraging studies thus far of convalescent plasma in treating COVID-19.

A large clinical study conducted by the Mayo Clinic found that patients who received transfusions with convalescent plasma within three days of being diagnosed with COVID-19 had a statistically significant lower average death rate than patients who received plasma four or more days after being diagnosed. The main knock against this study, though, is that it didn't include a placebo group. 

Results from randomized and controlled clinical studies with placebo groups are needed before it is clear how safe and effective convalescent plasma therapies are in treating COVID-19. The FDA stated that its EUA isn't intended to replace any of the ongoing clinical trials. The agency still recommends that the designs of these studies "remain unaltered, as COVID-19 convalescent plasma does not yet represent a new standard of care based on the current available evidence." 

Who wins?

If convalescent plasma proves to actually lower death rates, COVID-19 patients will obviously be the biggest winners from the FDA's EUA of the therapy. However, there are also some companies that benefit.

On Monday, several biotech stocks, including ADMA Biologics (ADMA -3.21%) and Kamada (KMDA -1.15%), soared as a result of the FDA's EUA. ADMA specializes in the collection of human plasma. Israel-based Kamada is currently evaluating a plasma-derived therapy in phase 1/2 testing for potentially treating COVID-19.

Emergent BioSolutions (EBS -5.94%) is another possible winner, although its stock didn't jump on the EUA news. The company partnered with Mount Sinai Health System and ImmunoTek Bio Centers to test a hyperimmune globulin COVID-19 therapy derived from convalescent plasma as post-exposure prophylaxis of COVID-19 in front-line healthcare workers. This effort received $34.6 million in funding from the U.S. Department of Defense.