(NEW YORK) — One year ago, on Dec. 14, 2020, Sandra Lindsay, an intensive care nurse from Northwell Health, became the first American to roll up her sleeve and receive a COVID-19 vaccine, following the green light from federal authorities.

“That day, when that needle pierced my arm, all I felt was this huge boulder, this weight just roll off my shoulders. I’m always optimistic, but my light got even brighter that day,” Lindsay told ABC News.

Lindsay’s image rapidly circulated across the country, a symbolic representation of the light at the end of the tunnel after the pandemic had forced families apart, shuttered businesses and schools and confined millions of Americans to their homes.

“I just felt hopeful for myself, for the entire country, for the world — that yes, the day that we’ve waited so long for healing is coming,” Lindsay said.

The country’s unprecedented creation and rollout of the vaccine was once considered a nearly impossible feat, given that vaccine development is often a long and arduous process, requiring years of regulatory and manufacturing hurdles to be overcome before it can be made available to the general public.

However, leaning on years of prior research on vaccine technology and with support from the federal government, the process was expedited, allowing for emergency authorization of the shots less than a year after work began.

“When the vaccine first became available a year ago, it seemed miraculous that a vaccine could be developed, rigorously tested in large clinical trials and ready to go in less than a year after the virus was identified,” Dr. Stephen Morse, professor of epidemiology at Columbia University, told ABC News. “That’s an amazing accomplishment considering that we really didn’t have the infrastructure for a rapid national mass vaccination campaign when we started.”

Nevertheless, hundreds of millions of Americans are now inoculated — but tens of millions of others remain completely unvaccinated, an ongoing hurdle that experts say will likely result in the loss of tens of thousands of more lives.

Millions vaccinated but hundreds of thousands still lost to COVID-19

Nearly two years after the vaccine companies first raced to study the virus genome, around 600 million vaccine doses have been distributed and more than 200 million Americans — about 61% of the population — have been fully vaccinated.

“Overall, I think that the vaccine rollout has been a major success over the past year,” Dr. Cindy Prins, a professor of epidemiology at the University of Florida, said. “This took a lot of effort and flexibility, with public health professionals in different states tailoring the rollout to the needs of their own populations. … Looking back, I’m really in awe of what the U.S. has achieved in the past year.”

Pfizer, along with its partner BioNTech, was the first company to receive U.S. regulatory emergency use authorization for its COVID-19 vaccine. Reflecting on the one-year anniversary of the rollout, Pfizer CEO and Chairman Albert Bourla told ABC News he feels proud of what the company has accomplished over the last two years.

“I’m proud and proud for the people at Pfizer. I’m proud for everything that we’re able to do. They [made] the impossible possible, in the way that they manufactured, they brought the treatment, they brought the vaccine,” Bourla said, later adding, “We have the tools to control the situation and go back to our normal way of life.”

However, the road to vaccinate the country has not been easy.

Even with the Trump administration’s multi-billion dollar initiative, Operation Warp Speed, created to speed up the development, manufacturing and distribution of COVID-19 vaccines, as well as a subsequent push from the Biden White House to acquire vaccines and get Americans vaccinated, there have been inconsistent ebbs and flows of interest in the shots.

Over the last year, an average 1.3 million shots — including first, second and third doses — have been administered every day. Comparatively, an average of more than 1,300 lives have been reported lost to the virus each day.

When the first COVID-19 vaccines were administered last December, many hoped the shots would herald a return to normalcy. However, even with vaccines, the U.S. continues to lose thousands of lives every week.

The one-year vaccine anniversary coincides with yet another pandemic sobering milestone: 800,000 Americans reported lost to the virus. Since the first shots went into arms a year ago, approximately half a million Americans have died of the virus.

Of those lost in the last year, just shy of half — 230,000 — have died since mid-April of 2021, when President Joe Biden announced that the vaccine was widely available to every American over the age of 18.

“Since the unvaccinated are most likely to get serious disease and end up in the hospital, vaccination is lifesaving,” Morse said. “This week, we will reach 800,000 confirmed COVID-19 deaths in the U.S. At least a quarter of these deaths, and probably more, were preventable and didn’t have to happen if these people had been vaccinated.”

According to federal data compiled in September 2021, unvaccinated individuals had a 5.8 times greater risk of testing positive for COVID-19 and a 14 times greater risk of dying from it, as compared to vaccinated individuals.

Vaccine hesitancy an ongoing obstacle

Across the country, the issue of vaccine hesitancy remains an ongoing obstacle in the country’s fight against COVID-19.

About 93 million Americans remain completely unvaccinated, including 73 million Americans who are currently over the age of 5, and thus, eligible for a shot.

“I think we were unprepared for the ferocity of the negative response and how many were adamantly opposed,” Morse said.

According to a Kaiser Family Foundation poll released earlier this month, one in four adults remain unvaccinated, with about 14% saying they will “definitely not” get vaccinated. An additional 3% said they will only get the shot if they are required to do so for work, school or other activities.

In addition, despite the fact that all children above the age of 5 are now eligible to receive a shot, millions of youth remain unvaccinated.

About two-thirds of parents of elementary school-aged children are either holding off on getting their younger children vaccinated or refuse to do so, according to another recent KFF poll, conducted before the discovery of omicron.

Coronavirus infections among children continue to surge, currently accounting for about a quarter of all new cases.

“The challenge with having so many people remain unvaccinated is that the virus will circulate most efficiently among those people,” Prins said.

Issues of access still a roadblock for many Americans

Minority communities in the U.S. have faced disproportionate hardships in the pandemic. According to federal data, adjusted for age and population, the likelihood of death because of COVID-19 for Black, Latino and Native American people is approximately two to three times that of white people.

Vaccination rates among Black and brown Americans have notably improved since the first months of the pandemic, though some groups are still lagging behind in the rollout.

Despite representing 12.4% of the U.S. population, Black Americans currently account for 10.1% of those fully vaccinated against COVID-19.

“It’s OK to have questions, but go to trusted sites,” Lindsay, who has become a vaccine advocate, said. “Everyone knows that we are scarred from historical events. But you’ve got to put that aside. So much has happened since all those terrible things. Safeguards have been put into place to ensure that these terrible experiments don’t happen again.”

Issues of access, particularly in minority communities, remain a significant hurdle for many to get vaccinated.

“The access issues still exist, and I think that they can be even more challenging now, because a lot of the mass vaccine clinic and mobile clinic efforts have given way to vaccines being distributed by pharmacies or doctors’ offices,” Prins said. “There are many neighborhoods in the U.S. where people don’t have access to a pharmacy or physician’s office and may not have good transportation to be able to get to one easily.”

According to an ABC News’ analysis of pharmacy locations across the country conducted earlier this year, there are 150 counties where there is no pharmacy, and nearly 4.8 million people live in a county where there’s only one pharmacy for every 10,000 residents or more.

“While it is important to celebrate the incredible science, engineering and public health expertise that went into designing and delivering so many vaccines this past year, we must also remember the lack of equity both nationally and internationally in who has been vaccinated,” said Samuel Scarpino, managing director of pathogen surveillance at the Rockefeller Foundation. “As we move forward, it is critical that we address the systemic barriers preventing more equitable delivery vaccines.”

‘Now is the time to take action’

Ultimately, experts concurred that the country’s vaccination efforts are far from over.

“If we had controlled the virus early on, we could have avoided this. More recently, if everyone had been vaccinated, we could have prevented many deaths and much suffering. Too late now, but still not too late to use the vaccine to soften the landing,” Morse said.

With the waning of immunity over time and the potential that the omicron variant could chip away at efficacy, experts are urging Americans to slow the rise of infections by getting vaccinated and boosted.

“The virus isn’t going anywhere,” Lindsay added. “Now is the time to take action, get informed and make the right decision for yourself and for your loved ones.”

ABC News’ Sony Salzman and Chris Donato contributed to this report.

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