u/Jazzlike-Cup-5336

Yesterday, the FDA posted their decision summary after recently granting 501(k) clearance to Aptitude Medical’s Metrix molecular COVID-19 test: https://www.accessdata.fda.gov/cdrh_docs/reviews/K253453.pdf

Recent post on the clearance: https://www.reddit.com/r/ZeroCovidCommunity/comments/1vogxvw/aptitude_metrix_updates_fda_has_granted_510k/

Supporting the clearance are 2 new studies evaluating 1,171 symptomatic individuals from the 2023-2024 (540) and 2024-2025 (631) respiratory seasons; much larger than the 357 previously evaluated to grant Emergency Use Authorization (EUA).

In short: The test performed similarly across the board, and they were able to tighten the confidence interval on the false positivity rate with the much larger sample size. For some reason, there was a fairly high invalid rate for the 2023-2024 season specifically, which is something that I know folks often complain about with the platform…not really sure what the deal was there.

Previous EUA data:

• Age 2+, 282 asymptomatic and 75 symptomatic (357)

• Sensitivity: 96.6% (59/61), 95% CI 88.8–99.1%

• False positive rate: 1.0% (3/293), 95% CI 0.2-2.8%

• Invalid rate: 5/357 (1.4%)

New 2023-2024 data:

• Age 14+, 540 symptomatic

• Sensitivity: 95.4% (83/87), 95% CI 88.9–98.2%

• False positive rate: 0.4% (2/451) 95% CI 0.1-1.6%)

• Invalid rate: 31/540 (5.7%)

• Invalid rate after retesting: 4/540 (0.7%)

New 2024-2025 data:

• Age 14+, 631 symptomatic

• Sensitivity: 96.9% (62/64), 95% CI 89.3–99.1%

• False positive rate: 0.5% (3/564), 95% CI 0.2-1.5%

• Invalid rate: 3/631 (0.5%)

• Invalid rate after retesting: 2/631 (0.3%)

New combined data:

• Age 14+, 1,171 symptomatic

• Sensitivity: 96.0% (145/151)

• False positive rate: 0.5% (5/1,015)

The IFU sheet containing the old EUA data: https://www.fda.gov/media/162403/download

In June 2026, HHS announced that Emergency Use Authorization (EUA) declarations related to the COVID-19 pandemic would be ending, giving a 12-month grace period to drugs and a 6-month grace period to medical devices to transition to full approval/clearance pathways. This decision impacts Aptitude’s Metrix molecular testing platform, however, Aptitude stated at the time that the FDA had already accepted their 510(k) submission for both the Metrix COVID-19 Test and the Metrix COVID/Flu Test.

On August 7th, the FDA granted clearance to the COVID-19 test.

Separately, while looking into this, I noticed today that the COVID/Flu combo tests are currently unavailable for purchase, with the product pages for both the single tests and the 25 pack returning a 404 error.

Lately, the stock of single tests had been short-dated (an expiration date of August 12th) and were being offered at a discounted $25 as a result. So, that could be a potential explanation. However, the most recent listed expiration date for the 25 pack was January 2027, so that product wouldn’t fit the same mold. Additionally, as far as I’m aware, Aptitude has never actually deleted a product page because of a stock issue, they will just list the item as “out of stock” until it returns. I’ve emailed them asking if they can share any information about what’s going on with the combo tests, and will update if I hear back.

EDIT:

Update: I received a reply from Aptitude that the single COVID/Flu tests are indeed just sold out (predictable), and there’s no estimation yet for when they’ll be back in stock. They claim that the 25 pack is still available for purchase.

Now, onto the website: They seemed a bit surprised at the 404 errors, but both product pages are now back up. The product pages list both the single and 25 pack as being sold out, the latter contradicting the email. Maybe that’ll just take a minute to sort out.

Here is the reply:

> I can confirm that the Metrix COVID/Flu Combo Test has not been discontinued.

> Our COVID/Flu Combo single-pack is currently out of stock. We are working closely with our manufacturer to restock the single-pack tests with a newer batch that has a longer expiration date. However, we don’t currently have an exact timeline for when they will be available.

> If you’d like, I’d be happy to add you to our waiting list and notify you as soon as the new batch is back in stock.

> In the meantime, if you need tests sooner, we do have the COVID/Flu Combo 25-pack available, with an expiration date of January 2027.

> Regarding the 404 error you mentioned, if you’re still having trouble accessing the product page, could you please send me a screenshot of what you’re seeing? I’ll forward it to our internal team so we can look into the issue.

So, the Burger King app, as far as I know, offers the quickest and easiest refunds in fast food, so I’m pretty frequently taking advantage of that. If they give me an incorrect item or forget an item, I’ll always go in the app and tell the chat bot, and I always receive a coupon for greater than the item’s value every time. And it happens a lot, because, well, they mess up a lot, just like any fast food restaurant in 2026. But at any other restaurant, where the refund process isn’t as easy as spending 60 seconds with a chatbot, I’ll usually just ignore the minor issues.

Anyway, I’m just wondering, since I end up doing it fairly frequently:

• Do individual stores or employees ever get contacted/notified about refunds?

• Can employees specifically see when you use a customer support coupon for an order (and would they potentially think anything of that)?

• Are there ever any consequences for individual employees for refund-related issues?

I doubt that those things would be an issue, but I would just hate to be known by local staff as a “problem customer”, or even worse, cause someone to get in trouble, because fast food is never that serious. So I just wanted to get a vibe check on the situation

By now, you’ve probably seen at least some information floating around over the past few years that over-the-counter antihistamines could be a beneficial addition to COVID treatment protocols.

The science behind H2 blockers is more robust, and picking a product is also a much easier task. There’s really only one on the market that makes sense, which is Famotidine/Pepcid. In 2022, we got this small randomized clinical trial suggesting that Famotidine during an acute infection can improve the rate of symptom resolution: https://gut.bmj.com/content/71/5/879

For H1 blockers (the more common antihistamines that you probably think of (eg. Benadryl)), there is also speculation that they may be beneficial in treating acute COVID, however, the choice of selecting a product is a lot more complicated, with close to a dozen potential options on the market.

The theory that H1 blockers may be beneficial mainly stems from this 2024 paper, which demonstrates that the H1 histamine receptor can act as an alternative receptor for SARS-CoV-2 entry, in addition to ACE2: https://journals.asm.org/doi/10.1128/mbio.01088-24. Therefore, an H1 blocker that competitively binds to H1 should theoretically work to prevent SARS2 entry.

From what I’ve been able to identify, there are 3 options that likely stand out above the others:

• Fexofenadine (Allegra)

• Cetirizine (Zyrtec)

• Levocetirizine (Xyzal), the active, purified component of cetirizine

That 2024 paper also studied the IC50 of 11 different antihistamines, which is the concentration that would be required to inhibit SARS2 binding by 50%. Their choices of antihistamines, though, aren’t very helpful, because those 11 only included a couple of OTC options that would make sense for outpatient COVID treatment, like Benadryl and Claritin. However, the takeaway is still important - although there was some slight variation, the IC50 of all 11 antihistamines fell into the range of 1.6 to 3.6 micromolars (μM). For the sake of making a choice, since it’s the only thing that we can really do, we can assume that most available OTC antihistamines will also likely fall within that same range, or at least be similar.

From that starting point, we can look at the Cmax of available OTC antihistamines, which is the maximum plasma concentration that they achieve in the body, and comparing them to the IC50 range that the study lays out. At the typical oral dose, these are the Cmax concentrations of some popular OTC options:

• Fexofenadine (Allegra) - 0.98μM

• Cetirizine (Zyrtec) - 0.80μM

• Levocetirizine (Xyzal) - 0.69μM

• Diphenhydramine (Benadryl) - 0.27μM

• Dimenhydrinate (Dramamine) - 0.15μM

• Chlorpheniramine - 0.055μM

• Loratadine (Claritin) - 0.020μM

As you can see, the 3 that I mentioned are the only options that come anywhere close to reaching the desired concentrations.

Since any theoretical benefit is based solely on the mechanism (ie. no trials yet), combined with the fact that none of the options actually do reach the required Cmax, I probably definitely wouldn’t suggest H1 blocking antihistamines as a blanket treatment that everyone infected should automatically take. But it’s certainly a legitimate pathway to consider, and is fairly low-risk.

So, if you do want to add an antihistamine, why not just select the best performing in Cmax, which is Fexofenadine (Allegra)? Well, there are some other individual characteristics to consider.

Fexofenadine (Allegra) is the one option that comes with essentially no risk of drowsiness, while both Cetirizine (Zyrtec) and Levocetirizine (Xyzal) do both typically come with with at least slight drowsiness, the caveat being that they’re also slightly more potent at their job of H1 blockade. Allegra is more polar, meaning that it’s less “membrane sticky”, which means that it crosses the blood brain barrier less, which is why we get the benefit of no drowsiness. However, that relative lack of concentration at membranes also means that it may not perform as well in the SARS2 cell entry context, since that area is where the viral entry is happening. This could theoretically increase the IC50 of Allegra, making it more similar (or even a slightly worse option) when compared to Zyrtec or Xyzal. Our best guess is that it probably wouldn’t increase the IC50 dramatically, but it’s still something that should be considered.

So, TLDR, my recommendation would be:

• If you want the safest bet with an all-around favorable profile, and you don’t mind some drowsiness or plan to take it at bedtime, then the best options are either Cetirizine (Zyrtec) or Levocetirizine (Xyzal).

• If you don’t tolerate drowsiness at all, or if you want the option that may perform better, but does have some question marks surrounding its mechanism for blocking SARS2 cell entry, then the best option is Fexofenadine (Allegra).

A quick comparison of both trials:

COVID-OUT:

• Dec 30, 2020, to Jan 28, 2022

• n = 1,126

• Symptomatic COVID for <7 days

• Outpatients aged 30-85, either overweight or obese

• 55% with at least 2 prior SARS2 vaccines

• No prior SARS2 infection

• Percent with PASC symptoms (cumulative) by day 300: 6.3% with metformin vs. 10.4% with placebo

• Hazard ratio [HR]: 0.59 (95% CI 0.39 to 0.89)

• When started within 3 days of symptom onset: Hazard ratio [HR]: 0.37 (95% CI 0.15 to 0.95)

ACTIV-6:

• Sept 19, 2023 to May 1, 2024

• n = 2,983

• Symptomatic COVID for <7 days

• All outpatient adults aged 30+

• 54% with at least 1 prior SARS2 infection

• 68% at least 2 prior SARS2 vaccines

• 83% either prior infection or vaccine

• Percent with PASC symptoms on day 180: 2.3% with Metformin vs. 3.0% with Placebo

• Adjusted risk of symptoms on day 180 was 0.8 percentage points lower with metformin (95% credible interval [CrI] -2.2 to 0.6)

• Risk ratio [RR]: 0.79 (95% CrI 0.474 to 1.230)