- Senior Washingtoncorrespondent Tara Mergener

is here with the latestin tonight's top story.

Tara?

- Well, John and Jenna, now that the FDA

has OK'd the vaccine for emergency use,

nearly three milliondoses are making their way

to every corner of the country.

It's the nation's biggestever vaccination push.

- The development of a COVID-19 vaccine

is nothing short of revolutionary

and I hope everyoneappreciates the importance,

the significance, thehistory of this moment.

- Through President Trump'sOperation Warp Speed,

substantial quantities of asafe and effective vaccine

within a year after the viruswas first known to the world.

- [Tara] Healthcare workers,seniors, and first responders,

priority one.

In all, 145 locationsreceiving vials Monday.

- [Woman] One safe.

- Get my COVID shot and goright back to my COVID patients.

- [Tara] Rolling outof the Pfizer facility

in Kalamazoo, Michigan,loaded onto planes,

and distributed across the country.

- [Sandra] I feel hopeful today, relieved.

- [Tara] Research shows thevaccine is 95% effective.

- This is truly a very innovative moment,

unlike anything else in history,

by the nature of thekind of vaccine this is.

- [Tara] In Chicago,Rush University Hospital

transforming its lobbyinto mass vaccination bays.

In New York,

one group vaccinating 56,000frontline workers by afternoon.

The rollout comes at a crucialmoment of the pandemic.

A record 108,000+ Americans

are in the hospitalright now with COVID-19.

- The next number of weeksare gonna be hell, I fear.

So we're begging peopleto please, please, please

don't let your guard down.

- [Tara] Health experts say75 to 80% of the US population

has to be immunized before herdimmunity could take effect.

The goal is to reach thatpoint by May or June.

Now, there has been some concern

about whether Americanswill trust the vaccine

enough to get it,

but according to a newABC News-Ipsos poll,

more than 80% do say they want the shot.

John and.