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Some promising news was announced Monday on the COVID-19 vaccine front.

And along with it, some warnings from health experts.

Pfizer announced its COVID-19 vaccine is 90-percent effective at protecting people from getting seriously ill when they are infected with the virus that causes COVID-19.

But the Food and Drug Administration says study participants need to be monitored for two months for side effects.

And medical professional say the vaccine study results need to be peer-reviewed.

Cautious optimism is the prescription now.

Dr. Sadiya Khan is an assistant professor of preventive medicine at Northwestern Medicine.

“It’s great to be able to discuss some optimistic and good news,” Khan said. “We are very excited. But it is important to see the data and that’s what we’re still waiting for.”

44,000 people enrolled in Pzifer’s U.S. COVID-19 vaccine study.

“What Pfizer is reporting and in that setting they are reporting a 90% advocacy,” Khan said.

But some say even if it works they are concerned about getting it. Doctors say, even though fast tracked, the vaccine trial followed protocol.

“The concerns related to safety are absolutely legitimate and one of the reasons why when this vaccine showed promising results in early study, such as phase 1 and phase 2 studies in the summer,” Khan said. “It wasn’t released then, knowing we had a dangerous virus on our hands. We held off and really waited for this critical data in phase 3 study.”

In the vaccines most of us typically get, a weakened or inactivated virus like polio or measles is given to trigger and immune response when the body encounters the real thing. The antibodies remain on high alert recognizing and battling the foreign invader.

But for COVID-19, scientists simply used the classic spiked protein on the coronavirus as a target, the immune system recognizes the spikes in recovered patients.

“So it’s a different approach to herd immunity,” Khan said. “Instead of being exposed to the virus itself, you’re being exposed to a key part of the virus and will develop antibodies to fight it off if you were ever to get the virus.”

For those who never had the virus, here is a how this vaccine works: Pfizer used two elementsL An MRNA substance and a lipid nanoparticle.

Patients will get two shots.Together they give the body genetic instructions to boost immunity against a specific pathogen — in this case, the characteristic spikes in SARS-CoV-2, the virus that causes COVID-19.

“Early on, Pfizer made a contract to deliver 100 million doses in which two doses are needed for 50 million people by December with the option to develop 500 million more,” Khan said.

In addition to doses, shipping, refrigerating and storing, the Pfizer vaccine will pose other challenges. As the efficacy of the vaccine is tested and patients are monitored, manufacturing is ramping up as well.

Pfizer says it is on track to collect the FDA required two months of safety data by the third week of November and could file for an emergency authorization shortly thereafter.