Though the U.S. already has three approved COVID vaccines being distributed across the country, there have been some discussions about two others circulating elsewhere in the world: the AstraZeneca vaccine and the Novavax vaccine.
Both companies expect their vaccines to be considered for U.S. approval this spring, but what separates them from the ones already being administered in the U.S.?
Here's a look at the two vaccines:
Chicago's top doctor said the COVID-19 vaccine developed by AstraZeneca and the University of Oxford could appear before the U.S. Food and Drug Administration sometime in April.
"In addition to the three that have been approved or have been authorized here in the U.S., we're keeping our eye on AstraZeneca," Arwady said Thursday. "It's already in use in Europe and some other countries and it's been, you know, it's been having its studies here... we'll see. They weren't done yet, but there's been some speculation that, you know, possibly in April we could see that vaccine."
Arwady noted the AstraZeneca vaccine "has performed well broadly," but there were concerns it may not be as effective against the coronavirus variant that emerged in South Africa.
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"There's been some extra attention sort of looking at looking at the vaccine in that context, but it has generally also been a very good vaccine," Arwady said. "And I wouldn't be surprised if we see that one potentially going, you know, getting put before the FDA in April."
But that concern has also been raised with other vaccines.
The variant from South Africa, for example, reduced Pfizer-BioNTech's antibody protection by two-thirds, according to CNBC, citing a February study. Meanwhile, Moderna's neutralizing antibodies dropped six-fold, according to the report.
To compare each of the three coronavirus vaccines currently available to Illinois residents, click here.
But other concerns have sparked recently surrounding the AstraZeneca vaccine.
The concerns prompted some countries to pause use of AstraZeneca’s coronavirus vaccine, despite a lack of evidence the shot was responsible for clots.
Denmark was the first to temporarily halt use of the AstraZeneca vaccine Thursday after reports of blood clots in some people. Norway, Iceland and Bulgaria followed suit and suspended use of the vaccine.
Thailand and Congo have also delayed use of the vaccine, pending an investigation, while Italy and Romania stopped using shots from one particular batch. Austria has also halted use of doses from a single, but different, batch.
France, Poland and Nigeria, meanwhile, said they would continue using the AstraZeneca shot even as national regulators investigate.
"An analysis of our safety data of more than 10 million records has shown no evidence of an increased risk of pulmonary embolism or deep vein thrombosis in any defined age group, gender, batch or in any particular country with COVID-19 Vaccine AstraZeneca," a spokesperson for AstraZeneca told CNBC.
The European Medicines Agency said "there is currently no indication that vaccination has caused these conditions, which are not listed as side effects with this vaccine."
"The position of EMA’s safety committee PRAC is that the vaccine’s benefits continue to outweigh its risks and the vaccine can continue to be administered while investigation of cases of thromboembolic events is ongoing," the agency stated.
Novavax, which is the lesser known of the remaining vaccines, Arwady said, is another being monitored.
The company has said it expects to gain U.S. approval by May, a timeline Arwady said remains possible.
"Hundreds of companies have been sort of looking at vaccines, but I'd say Novavax is the other one here in the U.S. I'm kind of keeping my eye on, going further behind in the trials, but their initial data looked good," she said. "Could that be sort of May for another vaccine? I think possibly."
Novavax's trials in the U.S. and South Africa are ongoing. The company cannot apply for emergency use authorization in the U.S. until the American trials are complete.
But according to the company's Phase 3 clinical trial in the U.K., Novavax's vaccine is more than 96% effective in preventing mild and severe illness for the original coronavirus strain and 89% overall. That efficacy drops to roughly 55% when it comes to the South African variant, according to an analysis of its phase 2b trial in South Africa.
"We are very encouraged by the data showing that NVX-CoV2373 not only provided complete protection against the most severe forms of disease, but also dramatically reduced mild and moderate disease across both trials. Importantly, both studies confirmed efficacy against the variant strains,” Stanley C. Erck, president and CEO of Novavax, said in a statement.
Novavax is also working on a booster shot that could be tested as early as April, a spokesperson for the company told Scientific American.
Novavax is a two-dose "protein subunit vaccine," meaning it contains harmless pieces of the surface spike protein that directly trigger the immune system.
Erck told NPR the Novavax vaccine is similar to the flu vaccine in that it can be tweaked "very easily" depending on which strain of the virus is circulating.