SALT LAKE CITY — Utah's newest public health order extended the statewide mandate for wearing masks to stop the spread of the coronavirus, offering better insight into one of the hottest questions that have been asked for months during the COVID-19 pandemic: When can we take the masks off?

While no specific date was set in writing, the Utah Department of Health on Tuesday provided an important benchmark that would trigger the process to lift mask mandates.

We now know that counties with "low" transmission rates will no longer have statewide requirements eight weeks after the state receives a little more than 1.63 million first — also referred to as "prime" — allocated doses of the COVID-19 vaccine.

A prime dose is currently either the first dose of the Pfizer-BioNTech or Moderna vaccines but is set to also include the one-dose Johnson & Johnson vaccine that is nearing final Food and Drug Administration approval.

Why 1.63 million?

The exact number to begin the process to lift the mask mandate isn't arbitrary at all. The number represents 70% of Utah's adult population, said Tom Hudachko, a spokesperson for the Utah Department of Health.

As noted by the Cleveland Clinic, it's expected that about 50% to 80% of the population would need to be vaccinated to reach herd immunity. The New York Times reported that some public health experts place the range between 70% and 90%. Seventy percent was also a figure estimated early on in the pandemic.

There are also early signs that all 1.63 million prime vaccine doses would be administered once the allocated number is reached. A majority of the two age groups in state health department data that have had access to the COVID-19 vaccine for over a month now have received at least one dose. The data show that 71% of Utahns ages 70 to 79 and 69% of Utahns ages 80 or older have received a prime vaccine.

When will we reach 1.63 million?

There are still a lot of vaccines that need to be allocated for Utah to reach 1,633,000.

The health department reported Tuesday the state has had 444,905 first doses allocated with over 410,000 Utahns receiving at least the first dose of the vaccine.

That means over 90% of allocated first-dose vaccines to date have already ended up in Utahns arms (again, showing the popularity of the vaccine so far), but it also means the department, by its own numbers, on Tuesday was about 27% toward what it would need to get to 1.63 million.

The good news is that there have been more vaccines delivered over the past few weeks than in the first few weeks after they became available. The bad news is the number of vaccines allocated to states has been fluid since the beginning and remains so now, which makes it difficult to project an exact answer as to when Utah will reach a certain number.

This fluidity was the basis of a New York Times data model that looked at the nation's vaccination process as a whole. It found that at its current pace of 1.7 million shots per day, the U.S. would reach vaccine immunity by November but hit total immunity — the number of people vaccinated plus the number of people who became immune after recovering from the illness — by June.

If it was sped up to 3 million shots per day as a result of a "supply increase," then the total immunity could be reached as early as May with vaccine immunity hitting 70% by July.

Still, there are some rough estimates as to when Utah could get to 1.63 million.

On Feb. 4, Gov. Spencer Cox said projections of the Moderna, Pfizer and Johnson & Johnson vaccines indicated about 130,000 prime doses allocated to Utah by early March. If that total was beginning the week of Feb. 28-March 6 and nothing changed, then there would take about nine weeks to surpass 1.63 million. The ninth week in that scenario is the week of April 25-May 1.

Cox added that the AstraZeneca vaccine, which is expected to go up for FDA approval in the coming weeks, could result in tens of thousands of additional prime vaccines every week beginning as early as April. The addition of a fourth vaccine would speed up the process, as well, and could move that date up sooner based on what was said a few weeks ago.

But again, the numbers have been fluid, and anticipated dose totals have already shifted since then. Officially, the Utah Department of Health still estimates that 1.63 million allocated prime doses will be reached "later this spring." That's when it's expected that there will be a prime dose allocated for about 70% of all Utahns currently eligible for the vaccine.

In an email, Hudachko told KSL.com Wednesday that new numbers presented by Congress this week indicates that it "certainly seems possible" that the state could reach 1.63 million allocated prime doses by the first week of May.

Should that be the case, it bodes well for the state's effort to ensure every adult in Utah who wants a vaccine will have access to one by late spring. It also gives ample time for the allocated doses to end up in Utahns' arms in the weeks after 1.63 million allocation mark is reached.

When will the masks come off?

OK, back to the new stipulation in the health order that went into effect Tuesday.

If Utah had that 1.63 million doses on Tuesday when that benchmark was announced, the counties with low transmission rates could then ease back on the mandate as early as April 20.

Related:

Utah's mask order extended; 1st benchmark to lift requirement defined

Masks will still be required statewide for at least the next month, but we now know what would trigger the end of the requirement in some areas.

If the state does hit 1.63 million allocated prime doses at the start of May, then it's possible that some counties in Utah could be exempt from the mask mandate by late June. In fact, if the health department started the clock on May 3, the mandate would end on June 28 for some areas.

This could explain Cox's comment Tuesday, in which he tweeted: "I truly believe that we will be celebrating maskless in large groups by the 4th (if not sooner)."

There is a second component to the question "when can the masks come off?" and that revolves around case trends, based on the current health order. Had the order gone into effect immediately, only five counties in Utah would be affected. That's because Daggett, Garfield, Piute, Rich and Wayne counties are currently the only counties in the state in the "low level of transmission" category.

A county needs to meet at least two of these criteria to reach "low" transmission:

• A countywide "test over test" positivity rate below 5%
• A 14-day case rate fewer than 101 per 100,000 people
• Statewide seven-day average intensive care unit bed utilization less than 69% and statewide seven-day average COVID-19 ICU utilization rate below 6%

That's where the administering of the allocated vaccines still comes into play. At the same time, COVID-19 trends are beginning to tilt in the right direction. The statewide seven-day rolling average for new COVID-19 cases has dropped 56% over the last four weeks — from Jan. 25 to Monday — based on data obtained Tuesday. The ICU utilization of all hospitals across the state fell to 69% on Tuesday; about 18% of those ICU needs were tied to COVID-19.

For those downward trends to continue in the coming weeks, health experts advise, and the health order mandates that Utahns wear their masks in all public areas inside and outside, physically distance themselves from other households, and wash their hands thoroughly.

The masks will be allowed to come off only when the appropriate number of vaccines needed are allocated and COVID-19 case trends remain down.

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