Why are 1,500 Americans still dying from COVID every week?

More than three years into the pandemic, hundreds of Americans are still dying from COVID-19 every week.

For the week ending Dec. 9, the last week of complete data, there were 1,614 deaths from COVID, according to the Centers for Disease Control and Prevention (CDC). The last four weeks of complete data show an average of 1,488 weekly deaths.

By comparison, there were 163 weekly deaths from the flu for the week ending Dec. 9, according to CDC data.

While high, these COVID death figures are still lower than the high of 25,974 deaths recorded the week ending Jan. 9, 2021, as well as weekly deaths seen in previous winters, CDC data shows.

The current "weekly rate of COVID mortality is similar to what we were getting per day at [the worst] parts of the pandemic. So, proportionally, we're in a completely different place than where we were, thankfully," Dr. Cameron Wolfe, a professor of infectious diseases at Duke University in North Carolina, told ABC News. "But there's still a pretty significant mortality; 1,500 patients dying every week is unacceptable, frankly."

Experts said there are several reasons why people might still be dying from the virus, including not enough people accessing treatments or getting vaccinated as well as waning immunity.

Additionally, if more people get sick, even if in lesser numbers than in previous waves, it will naturally lead to more people becoming hospitalized and, in turn, dying.

"We do have very good vaccines that [researchers] have been able to adjust as the variants have changed and very good treatment options that have been shown to decrease the risk of hospitalization as well as deaths," Dr. Shivanjali Shankaran, an associate professor of infectious diseases at Rush University Medical Center in Chicago, told ABC News.

"However, if we're not accessing those particular tools, then having them doesn't sort of make any difference," Shankaran added.

Too few people getting vaccinated

As of Jan. 5, just 19.4% of adults aged 18 and older and 8% of children have received the updated COVID vaccine, CDC data shows. Additionally, just 38% of adults aged 65 and older, who are at higher risk of severe illness, have been vaccinated.

The updated vaccine is targeted against variants that are related to XBB, an offshoot of the omicron variant.

Currently, JN.1, a descendant of BA.2.86 -- which is itself descended from XBB -- makes up an estimated 61.6% of U.S. COVID cases, CDC data shows.

Although the CDC has suggested JN.1 may be more transmissible or better at evading the immune system than other variants, there is no evidence that available vaccines don't work.

"The longer someone has gone since their last vaccine, or their most recent infection for that matter, the more likely their COVID breakthrough would occur and the more likely it's going to be severe enough that they land in hospital" and potentially die, Wolfe said.

Experts said there may a level of vaccine fatigue and complacency in the population with people not getting the updated vaccine because they don't feel like they need it after getting the original vaccine and then subsequent boosters. This, however, doesn't account for waning immunity.

"[Vaccines] don't retain their memory as effectively as we might like, so if you were vaccinated short of more than 12 months ago, your chances of maintaining really good memory again from that vaccine is probably pretty poor at this point," Wolfe said.

For a high-risk person, this increases their chance of severe illness if they get infected. For lower risk people, this increases the risk of them spreading the virus to more at-risk groups, he added.

Americans not accessing treatments

COVID-19 treatments have evolved since the early days of the pandemic with antiviral pills available, particularly Paxlovid from Pfizer.

Paxlovid is three pills given twice daily for five days for those at high risk of severe illness. Initial clinical trial data showed Pfizer's pill reduced the risk of hospitalization and death for unvaccinated patients at risk of severe illness who began treatment within three days of symptoms by nearly 90%. More recent studies including omicron strains of the virus and vaccinated patients have upheld similar results showing the treatment cut the risk of hospitalization and death in half.

It's been a relatively underused treatment with some reports suggesting that in some states it's prescribed in less than 25% of cases -- and it may be another reason why deaths have increased.

Experts said there may be several factors at play.

"It's a combination of misunderstanding about who's eligible for Paxlovid, a misunderstanding about whether Paxlovid works and then sometimes trouble getting prescriptions," Dr. Megan Ranney, dean of the Yale School of Public Health, told ABC News. "Because we know, for example, that Paxlovid use is much lower in rural areas, as well as among those who have lower educational levels, so I suspect for Paxlovid that there is this kind of element of access as well."

Physicians may also feel hesitant to prescribe Paxlovid due to concerns about how the medication interacts with other prescription drugs or even due to instance of people experiencing a Paxlovid rebound, which is a recurrence of COVID symptoms.

"The data on rebound is still being figured out, but what's clear is that whether or not you get a rebound with Paxlovid, it absolutely decreases risk of hospitalization and death," Ranney said.

More infections mean more severe illnesses

Another reason for the increase is the sheer fact that more people getting sick naturally means more hospitalizations and more deaths, according to experts.

"It's nothing obviously like the omicron wave where we had just millions and millions of people getting sick, and because of that many more people going to the hospital and dying, but yeah, as the total number of people who are infected increases, then you are going to have a similar increase in the number of people who need hospitalization," Shankaran said.

For those who may be elderly or immunocompromised, even a case of mild COVID-19 can result in severe illness and even death.

Experts said the messaging to the public is the same as in earlier phases of the pandemic and advise that Americans remain diligent.

"The message is to be aware of your own risk factors, be aware of your own symptoms, recognize that vaccines provide protection, not only against getting sick but severity of sickness," Wolfe said. "That's the same message that we try and send for flu and RSV each year, it's no different."