The Centers for Disease Control and Prevention’s (CDC) new mask guidance is based on newfound data suggesting vaccinated individuals can spread COVID-19, despite that data appearing to show that the vaccines still reduce infectiousness of the disease by some amount.

When the CDC changed its mask guidance in late July to suggest that vaccinated people once again put on face masks in certain indoor settings, it eventually cited data from Provincetown, Massachusetts, alongside other studies which found vaccination doesn’t totally stop transmission of the virus. Absent from most corporate media reporting and some government messaging is that, according to the available data, breakthrough cases are still exceptionally rare and vaccinated people still don’t transmit the virus nearly as much as the unvaccinated.

The Provincetown data is taken from a small sample size — just 127 infected individuals who were vaccinated in addition to 84 partially or unvaccinated — it hasn’t been thoroughly peer-reviewed by outside experts due to how recent it is and it was taken from a highly-specific environment: July fourth partygoers from across the country frequenting indoor establishments during “bear week,” a celebratory occasion in the area for gay men.

According to the Boston Globe, less than 0.2% of vaccinated Massachusetts residents have had confirmed breakthrough cases, despite the Provincetown outbreak.

Nationally, the data on breakthrough infections is quite promising. As of July 26, when the Delta surge was already underway, just 4,641 vaccinated Americans out of 163 million had been hospitalized directly due to COVID-19, and 954 died, according to the CDC.

Less than 0.004% of people who have been fully vaccinated against Covid-19 experienced a breakthrough case resulting in hospitalization, and less than 0.001% have died from the disease, according to the latest data from the US Centers for Disease Control and Prevention.

— Ana Cabrera (@AnaCabrera) August 1, 2021

It’s worth noting that comprehensive breakthrough infection data isn’t available, partly due to the CDC not tracking it. The agency tracked all breakthrough infections until May 1, when it switched to only reporting breakthrough hospitalizations and deaths. Only about half the states in the U.S. publicly publish full breakthrough infection data in one way or another.

That lack of comprehensive, clear data clouds decision-making, experts say. “They’re making these decisions on the basis of extremely weak and unreliable data, and at the same time not doing the necessary work to reduce uncertainty among the population,” Dr. Vinay Prasad, professor in the Department of Epidemiology and Biostatistics at the University of California, San Francisco, told The Wall Street Journal.

An internal CDC document estimated there are around 35,000 breakthrough infections per week nationwide. An NBC News analysis of state data came up with a total of 125,000 in 38 states. “The actual number of breakthrough infections is significantly higher, and much harder to know with certainty, due to underreporting and lack of aggressive surveillance testing,” Dr. Paulo Verardi, associate professor of virology and vaccinology at the University of Connecticut, told the Daily Caller.

The CDC did not respond to the Daily Caller’s request for comment about why the agency stopped tracking breakthrough infections and what its future plans are for doing so.

With a foggy understanding of just how many breakthrough cases there have been, scientists at the CDC and elsewhere are forced to extrapolate from a fairly small number of data sets to try and grasp how transmittable the Delta variant is among vaccinated people. Obviously, the CDC feels confident that it’s infectious enough — or at least may be — to go backwards on mask guidance, but not every expert agrees. (RELATED: New York City To Become First In The US To Implement Vaccine Passports For Indoor Dining, Fitness)

“Although I think the CDC put back masks due to the larger number of mild breakthrough infections among vaccinated individuals in light of the delta variant, I think vaccine mandates would be much more effective than mask mandates to control the latest delta variant surge,” Dr. Monica Gandhi of the University of California, San Francisco told the Daily Caller. “Vaccinated people are less likely to be infected and I agree are likely less to transmit.”

Former Trump-era FDA commissioner and Pfizer board member Dr. Scott Gottlieb said breakthrough infections are “infrequent and when they occur, they’re typically shorter in duration (with less potential for spread) than in unvaccinated.”

Study: post-vax delta breakthrough infections are infrequent and when they occur, they’re typically shorter in duration (with less potential for spread) than in unvaccinated. “Vaccination is associated with faster decline in viral RNA load.” https://t.co/B009fsCPJ6 h/t @EricTopol pic.twitter.com/FmNnIxf1oU

— Scott Gottlieb, MD (@ScottGottliebMD) July 31, 2021

Gottlieb cited a study released on July 31 out of Singapore which found that while viral load in vaccinated and unvaccinated patients with the Delta variant were similar in the first 5-7 days of infection, the viral load in vaccinated individuals declined far more rapidly thereafter.

Gottlieb isn’t the only expert pointing to that Singapore study as evidence of their conclusion. Several experts who spoke with the Daily Caller also independently referenced that study, but not everyone interpreted the findings the way Gottlieb did. (RELATED: Former FDA Commissioner Scott Gottlieb: We’ll Be Past Delta Wave ‘In Another Two Or Three Weeks’)

“The CDC paper and the Singapore paper both show that there is a lot of virus in the nose of infected people whether they’re vaccinated or not… those CT numbers are high,” Dr. John Moore, professor of microbiology and immunology at Cornell University told the Daily Caller. “If there’s a lot more virus in the nose of infected people, and they’re breathing it out, sneezing it out in greater amounts, what’s the best way to stop it? You stop it with a mask.”

Moore argued that erring on the side of caution is the right approach until more information is available: “I think the CDC made the right call… everyone wants data to exist instantly, and it just doesn’t work like that.”

Data still does not show whether or not the equivalent viral load found in some of the vaccinated patients means they have an equivalent level of infectiousness to an unvaccinated patient. It’s generally been assumed by most medical professionals that a higher viral load makes one more infectious, but it isn’t known with certainty how the interaction between the vaccines and the Delta variant could change that.

“What we still do not know is whether this level of RNA copies translates into infectious virus. The vast majority of vaccinated people are expected to have antibodies against the virus in blood and tissues… these antibodies are likely to make the virus less infectious, but we do not know exactly by how much in the case of Delta,” said Dr. Janko Nikolich-Zugich, head of the Immunobiology Department at the University of Arizona.

Nikolich-Zugich, similarly to Moore, advised a cautious approach: “Until we do, we should treat the first 7-10 days in vaccinated people as infectious. Breakthrough cases can and should be considered infectious until proven otherwise. In light of all that, universal masking in indoor or densely populated outdoor settings would be reasonable and likely necessary to avoid further spread of COVID-19 until we achieve high levels of vaccination immunity.”

Conflicting data does exist. A sample of 50,000 vaccinated people in the United Kingdom, relatively few of which ended up with a breakthrough infection, found that they did carry a smaller viral load than unvaccinated carriers.

Link to the preprinthttps://t.co/HihmmLKOvn
Extensive PCR testing showed that fully vaccinated people had lower viral loads than un- or partially vaccinated, supporting decreased potential for Delta transmission

— Eric Topol (@EricTopol) August 4, 2021

Some have also pointed out reasons to be skeptical of the Provincetown data. In addition to being a small sample in a unique environment, the study only included those who chose to be tested, meaning it likely skewed toward those with more serious cases, which could paint an inaccurate picture of the typical viral load across all cases.

Also as in the Provincetown study it’s a convenience sample, meaning people who chose to be tested, and not a random sample of all infections. That likely biases the sample toward more severe infections since people with more severe symptoms are more likely to seek out testing.

— Nate Silver (@NateSilver538) August 3, 2021

Gandhi seemed to put more stock into the Singapore study than Provincetown, and took a more optimistic message from it than some of her peers. “The Provincetown study looked at viral loads at one single point in time based on CT values on PCR. This Singapore study looked at serial viral loads in breakthrough infections among vaccinated individuals and delta infections among unvaccinated individuals,” she told the Daily Caller. “Although the two groups had the same CT values on PCR at first, it was petty striking how quickly antibodies likely get on board in breakthrough infections to bring the viral load down.”

Despite the CDC altering guidance based largely on the Provincetown study (and perhaps the Singapore study, which Moore said the agency likely had early access to), the White House has urged people not to press the panic button. Instead, they argue, this all proves that the vaccines are actually working. (RELATED: ANALYSIS: Believe It Or Not, Trump Voters Are Not The Only Vaccine Resisters)

“VACCINATED PEOPLE DO NOT TRANSMIT THE VIRUS AT THE SAME RATE AS UNVACCINATED PEOPLE AND IF YOU FAIL TO INCLUDE THAT CONTEXT YOU’RE DOING IT WRONG,” tweeted Ben Wakana of the White House’s COVID-19 response team. Wakana criticized both The Washington Post and The New York Times for their coverage of the Provincetown data.

VACCINATED PEOPLE DO NOT TRANSMIT THE VIRUS AT THE SAME RATE AS UNVACCINATED PEOPLE AND IF YOU FAIL TO INCLUDE THAT CONTEXT YOU’RE DOING IT WRONG. https://t.co/gBkDbJ21xX

— Ben Wakana (@benwakana46) July 30, 2021

Completely irresponsible.

3 days ago the CDC made clear that vaccinated individuals represent a VERY SMALL amount of transmission occurring around the country.

Virtually all hospitalizations and deaths continue to be among the unvaccinated.

Unreal to not put that in context. https://t.co/BbmSNvQlrb

— Ben Wakana (@benwakana46) July 30, 2021

Some experts have emphasized a similar conclusion: what isn’t yet known isn’t yet known, but until scientists figure out how transmissible Delta is from the vaccinated, people should understand the vaccines are still highly effective at preventing hospitalization and death. They also still prevent infection in a majority of people, which de facto prevents transmission in and of itself.

So what do we not know?

Because Ct values are rough surrogate of transmissibility

We don’t know if actual spread among vaccinated people compare to unvaccinated

And big one: we don’t know if vaccinated asymptomatic folks spread

This is key for mask guidance

5/6

— Ashish K. Jha, MD, MPH (@ashishkjha) July 31, 2021

Upwards of 97% of COVID-19 deaths are still among the unvaccinated, according to the Kaiser Family Foundation, and research still shows that those who do succumb despite being vaccinated typically have a substantial number of comorbidities.

Everyone who spoke to the Daily Caller agreed on what ultimately will bring the pandemic to an end, whether mask mandates return or not: “What we need is to get more people vaccinated ASAP,” Verardi said.