Most Americans need to unite behind mask-wearing, social distancing, and handwashing if the new COVID-19 vaccines in the pipeline are to prevent an estimated 770,000 deaths by April 2021.

The latest forecast from the Institute for Health Metrics and Evaluation (IHME) at the University of Washington's School of Medicine show that even with a vaccine, the U.S. death toll might hit a staggering 770,000 by April 1.

This is the grim scenario in store if states don't act to bring current surges under control using the three key preventive measures and if they relax vigilance over the next few months meant to control the spread of the coronavirus.

IHME projections show that even with the expected vaccine rollout starting late December and gaining steam in the first three months of 2021, the United States might still see 539,000 deaths by April 1.

"Mass scale-up of vaccination in 2021 means we have a path back to normal life, but there are still a few rough months ahead," said IHME Director Dr. Christopher Murray.

"We must be vigilant in protecting ourselves at least through April, when, as our projections indicate, vaccines will begin to have an impact."

The U.S. still leads the world in the number of total coronavirus cases and deaths. As of mid-Friday, the total case count for the U.S. came to 14.0 million with 219,00 new cases on that day. According to data from the U.S. Centers for Disease Control and Prevention, total deaths since the pandemic began are now at 275,000, with 2,900 deaths on Friday.

The IHME forecasts show some 66,000 lives could be saved if mask-wearing increased to 95% combined with a vaccine rollout. This compares to a vaccine rollout scenario with current mask-wearing levels remaining the same.

Even with a vaccine, the death toll stands to hit 770,000 by April 1 if states don't act to bring current surges under control.

"Especially in the Northern Hemisphere, it's crucial for governments to impose or re-impose mandates that limit gatherings and require masks," said Murray.

"Where the winter surge is driving spikes in infections, there will be many people who can still become infected and possibly die before the vaccine is fully rolled out."

The latest IHME forecasts include rapid vaccine rollout scenarios, expected rollout, and no vaccine with corresponding fatality rates for each scenario. A rapid vaccine rollout might reduce the death toll to 528,000 in the U.S. by April 1.

IHME said the vaccine rollout in the U.S. would only reduce the death toll by 9,000 deaths by April 1.

A rapid vaccine rollout targeting high-risk groups can reduce the death toll from 548,000 to 524,000 deaths compared to no vaccination.

Starting February, the increase in warmer temperatures and rising vaccination rates will lead to steady declines in the daily death toll. This welcome drop will continue into March and the remaining months of 2021.