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WASHINGTON (Nexstar) — The Food and Drug Administration could approve a COVID-19 vaccine by the end of the week. Before they do that, though, they’re double-checking the data to ensure the vaccine is safe and effective.

Dr. Deborah Birx of the White House Coronavirus Task Force said talked about what the vaccine will and won’t do and why other safety measures will still be needed after a vaccine is approved. She said the FDA is also looking at what other factors impact the vaccine’s efficacy.

“They want to look at if there’s an evidence that after a single-shot there’s partial protection, because we usually don’t go from no protection to 95%,” Birx said. “Is there an age relationship to protection? Is there a race or an ethnicity relationship to protections?”

Dr. Birx said it’s likely the Pfizer and Moderna vaccines will both get FDA approval because they are very similar, but that doesn’t mean COVID-19 will immediately disappear from the US, partly because making enough doses will take time and also because of what is not known.

The companies say the vaccines provide protection from the disease.

“It protects against the hospitalizations and it protects against the fatalities,” Birx said.

What isn’t known is whether the vaccines prevent people from being carriers and spreading COVID-19, something called “sterilizing immunity.”

“Does it prevent replication so great that there’s no ability to transmit the virus?” Birx said. “And I think those are studies that require higher numbers.”

That’s why the CDC says, for now, mask wearing will still be recommended even after people receive the vaccine.