Pfizer on Friday announced that it will distribute fewer vials of Covid-19 vaccine doses in the United States than it had originally planned, because the company is now counting the extra vaccine doses that providers have found in the company's vials toward its commitment to deliver 200 million vaccine doses to the country by the end of July. However, extracting the additional doses requires special syringes that are in short supply, presenting a new challenge in America's vaccine rollout, experts say.

Related: The U.S. Covid-19 vaccination scenario planning guide

Pfizer to deliver fewer Covid-19 vaccine vials to account for extra doses

In December 2020, hospital pharmacists throughout the United States discovered that some vials of Pfizer's and BioNTech's Covid-19 vaccine that were supposed to contain five doses had enough remaining liquid for a sixth and sometimes seventh dose. Following the discovery of the extra vaccine doses, Pfizer filed a request to revise the language in FDA's emergency use authorization for the Covid-19 inoculation to formally acknowledge a sixth dose in each vaccine vial, the New York Times reports. On Jan. 6, FDA under former President Donald Trump's administration approved Pfizer's request to update its vaccine label to clarify that providers can draw six doses, rather five doses, from each vial.

Because of the update, Pfizer announced that it will now distribute fewer vaccine vials in the United States than the company originally had planned while still meeting its commitment to supply the country with 200 million doses of the vaccine by July. According to the Times, Pfizer can make the change because its contract with the federal government requires that the government pay Pfizer per dose, not of per vial.

Amy Rose, a Pfizer spokesperson, in a statement issued Friday said Pfizer "will fulfill our supply commitments in line with our existing agreements—which are based on delivery of doses, not vials."

Providers may struggle to squeeze out the extra doses, experts warn

But some experts say extracting the sixth dose from each vaccine vial may be difficult for some providers, because to do so, they need a special syringe—called a low-dead volume syringe—that is currently in limited supply.

"For Pfizer, the FDA approval of the overfill dose means it can fulfill its contract, which calls for doses, and receive full payment from the [United States] with almost seven million fewer vials. But many of those sixth doses might ultimately be discarded because distribution centers lack the proper tools," Sam Buffone a partner with the whistleblower law firm Black & Buffone and a former senior trial counsel in the civil frauds division of the Department of Justice, told the Washington Post.

"Low dead space syringes are niche products, and there has been minimal market demand based on health care provider needs," Troy Kirkpatrick—a spokesperson for BD, the world's largest syringe manufacturer—separately told the Post.

The Post reports that, in response to questions concerning FDA's approval of the updated label for Pfizer's vaccine, HHS said it did "notify the FDA of potential long-term shortages" of low-dead volume syringes, but "FDA's decisions on vaccine authorizations and approvals are made independently to preserve the integrity of [its] process."

According to the Post, FDA in a statement said it had considered the availability of low-dead volume syringe—as well as changes the World Health Organization and the European Medicines Agency had already made to allow pharmacists to use the extra vaccine doses—when deciding whether to approve Pfizer's request.

Separately, an FDA spokesperson told Politico, "By far most importantly, [FDA considered] the need to ensure that the maximum number of individuals were vaccinated in the United States as rapidly as possible, since using six doses from the vials will vaccinate 16.6% more Americans than five doses would."

In addition, President Biden in his administration's national Covid-19 response plan highlighted the need for manufacturers to produce more low-dead volume syringes, the Post reports. Under the plan, Biden's administration intends to invoke the Defense Production Act to ramp up production of the specialty syringes, officials in his administration have said.

Further, according to the Post, the Biden administration on Friday finalized an agreement with Pfizer that will allow the federal government to track which Covid-19 vaccine shipments contain low-dead volumes syringes and which shipments do not, an individual close to the negotiations who spoke with the Post on the condition of anonymity said.

Separately, CDC said it would start to increase the number of syringes it's delivering with Covid-19 vaccine shipments, Politico reports, after the agency on Thursday told state officials that it would begin counting Pfizer's vaccine vials as containing six doses. However, CDC said the additional syringes may not be low-dead volume syringes, according to Politico.

Biden admin officials raise concerns over limited vaccine supply

The change comes as top Biden administration officials on Sunday raised concerns about the United States' limited vaccine supply, though they also expressed some optimism about America's vaccine rollout improving.

CDC data shows that, as of Sunday morning, the federal government had distributed about 41.4 million doses of the country's authorized Covid-19 vaccines, and about 21.8 million Americans had received their first dose of the two-dose vaccines.

But CDC Director Rochelle Walensky during an interview on "Fox News Sunday" said the Biden administration isn't sure how many vaccine doses the country has left, because of a lack of data tracking the vaccine rollout. "One of the biggest problems right now is I can't tell you how much vaccine we have, and if I can't tell it to you then I can't tell it to the governors and I can't tell it to the state health officials," Walensky said.

Walensky added that she thinks the country's Covid-19 vaccine supply will "probably … be the most limiting constraint early on" when it comes America's rollout. However, she said the federal government is working with manufacturers to ensure vaccine supply issues do not continue to hinder the vaccination effort.

In light of the supply issues, CDC on Thursday released new guidance that recommends Americans receive their second dose of the two-dose Covid-19 vaccines "as close to the recommended interval as possible," which is three weeks after they receive their initial of the Pfizer and BioNTech vaccine and four weeks after they receive their initial dose of the Moderna vaccine. "However, if it is not feasible to adhere to the recommended interval, the second dose of Pfizer-BioNTech and Moderna Covid-19 vaccines may be scheduled for administration up to six weeks (42 days) after the first dose," the guidance states.

During an interview with CNN, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and the chief medical adviser for the Biden administration's Covid-19 response efforts, said, "What the CDC is saying, sometimes, the situation is stressed where it's very difficult to be exactly on time. So, we're saying, you can probably do it six weeks later, namely, two additional weeks." He added, "Quite frankly, immunologically, I don't think that's going to make a big difference."

Still, Kristen Nordlund, a spokesperson for CDC, stressed that clinicians and patients should try to follow the vaccine schedules recommended by Pfizer and BioNTech, as well as by Moderna, as closely as possible. CDC's "intention is not to suggest people do anything different, but provide clinicians with flexibility for exceptional circumstances," Nordlund said.

America continues to grapple with high rates of new coronavirus cases, hospitalizations, and deaths

While officials are grappling with rolling out America's authorized Covid-19 vaccines, the country continues to report persistently high rates of new coronavirus cases, hospitalizations, and deaths.

According to data compiled by the Times, U.S. officials on Sunday reported about 129,527 new cases of the novel coronavirus. As of Monday morning, officials had reported a total of about 25.1 million cases of the virus since America's epidemic began—up from about 24.6 million cases reported as of Friday morning.

According to the Times, the United States' average daily number of newly reported coronavirus cases over the past week was 170,559—which is down by 33% when compared with the average from two weeks ago.

As of Monday morning, data from the Times showed that the rates of newly reported coronavirus cases were "staying high" in five states that have had a daily average of at least 15 newly reported cases per 100,000 people over the past week. Those states are Connecticut, New Hampshire, North Dakota, South Carolina, and Virginia.

The Times' data also showed that, as of Monday morning, the daily average of newly reported cases over the past seven days was "going down" in Puerto Rico; Washington D.C.; and the remaining 44 states (except Hawaii), which all had been seeing comparatively higher rates of coronavirus transmission.

The U.S. Virgin Islands has had a comparatively lower case rate, but that rate was "going up" as of Monday morning, according to the Times. In Hawaii and Guam, meanwhile, rates of newly reported coronavirus cases were "staying low" as of Monday morning, the Times' data shows.

U.S. hospitalizations for Covid-19, the disease caused by the novel coronavirus, remained high as of Sunday, though the number of Americans hospitalized with Covid-19 has decreased significantly from the high of more than 132,400 hospitalizations reported earlier this month. According to data from The Atlantic's COVID Tracking Project, there were 110,628 Americans with Covid-19 hospitalized for treatment on Sunday, including 21,168 who were receiving care in an ICU and 6,989 who were on a ventilator.

According to data from the Times, U.S. officials reported about 1,815 new deaths linked to the novel coronavirus on Sunday. As of Monday morning, officials had reported a total of about 419,207 U.S. deaths linked to the virus since the country's epidemic began, up from about 410,336 deaths reported as of Friday morning.

(Weiland et al., New York Times, 1/22; Roubein/Owermohle, Politico, 1/22; Rowland, Washington Post, 1/22; Naranjo, Politico, 1/24; Smith, NBC News, 1/24; Chen, Axios, 1/22; New York Times, 1/25; "The COVID Tracking Project," The Atlantic, accessed 1/25; CDC data, updated 1/24).