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California has a new COVID-19 isolation guideline that differs from the CDC's. Under its , California residents with confirmed COVID-19 can end their isolation once they have not had a fever (without fever-reducing medication) for 24 hours and other symptoms are improving. In addition, asymptomatic patients do not need to isolate at all. Masking for 10 days is deemed sufficient.

Many of you have been asking me about this. Including The Boston Globe. First, I'll share my quotes from an on this in the Globe earlier this week. Then we'll go deeper.

• California's new policy is an example of harm reduction, which is an important concept. "When people are going to do something or nothing, you offer something they are more likely to do." The idea here is that given pandemic fatigue (this is year five), it's better to ask people something they'll do, rather than ignore a larger ask...but...
• That said, "I don't know how they came up with this. I suspect that they just chose something that people could remember." That's trouble, potentially. On one hand, the science isn't ironclad here. People without a fever have lower viral loads, but that's not airtight. So, I tend to think that the scientists behind this policy took some things that are true, and applied them broadly. Look, asymptomatic cases are probably less contagious. There's decent data for that. But asymptomatic is not the same thing as presymptomatic. When my colleague Michael Mina, MD, PhD, says, "symptoms do not reflect infectivity, and they never have," I mostly agree. You can have tons of symptoms and not be contagious. But it is also true that completely asymptomatic cases tended to have lower viral loads.
• Presymptomatic COVID-19, however, poses a real problem. This is my biggest issue with California's guidance. "You may have no symptoms until day three or four, and by that time your viral loads are off the charts, and you're a super spreader," I told the Globe. The problem is that California lets people who tested positive for COVID-19 but are not yet symptomatic roam free, albeit in a mask. That may be fine at first. But some will have their viral loads enter an exponential growth phase (i.e., go from not contagious to extremely contagious in a short period) just as symptoms may be starting to appear. These are preventable super spreaders that the new guidance does nothing about, and could make worse.
• If your rapid COVID-19 test line is bright (brighter than the control line), and the test turns positive quickly, "I don't care what symptoms you have, you need to isolate." As I've before, the brightness of your test line has meaning. A bright and fast result means you are likely extremely contagious. (The meaning when the results are positive but less dramatic are a little more complicated; you're likely still contagious to some degree, but the magnitude is harder to know.)

What Didn't Make It Into the Globe (and the Headline Nobody Is Picking Up On...)

I had more to say to the Globe's health journalist Adam Piore, but not everything can fit into the paper. So, here are some further thoughts I have that we touched on during our conversation earlier this week:

More on harm reduction. People who are truly asymptomatic are probably less contagious, but they still may be contagious at times. People who no longer have a fever are less contagious than those with fever; but they still may be contagious. Yes, something is better than nothing; I am just not sure where they got this particular "something."

To be fair, the California guidance is all based on true things. The question is whether this policy effectively decreases spread or not. It might -- and if the scientists have modeling for this, I'd love to see the results. But I'm worried that any modeling they performed may have badly misunderstood the distinction between asymptomatic and pre-symptomatic cases, and the unique implications that these situations carry.

Why you tested matters. It's one thing if you get a positive test after a couple days of symptoms. In that context, California's guidance is based on data that show that decreasing viral loads often (but not always) correlate to reductions in symptoms. But if you tested positive because your roommate has COVID-19 and you're worried you might have caught it from them, this guidance misses the mark and potentially lets you become a superspreader. For example, if you test positive a couple days after an exposure but do not have symptoms, you don't know when your viral load will start going exponential (the time when you're at highest risk of spreading the virus) and whether symptoms will appear just before, during, after that phase, or never.

Context matters. Some degree of spread of COVID-19 on a college campus is a lot more tolerable than some degree of spread in healthcare facilities like nursing homes or acute rehab facilities where your dad goes after that hip replacement. Which leads to...

This next one should have been a headline. (In fairness, I hadn't fully noticed this myself when I spoke to the Globe.) The California guidance actually implies, but does not explicitly state, that many or most healthcare workers should not go to work for 10 days after a positive COVID-19 test. It says, "Avoid contact with those who are at higher risk for severe COVID-19 for 10 days." To me, that says that healthcare workers should not see many of their patients during that time. I wholeheartedly agree.

If there is any thing we 100% must be doing, it is preventing the spread of this virus to the highest-risk individuals. Healthcare workers and others who work closely with high-risk populations need to get paid sick leave to cover their contagious windows (ideally, as determined by two negative rapid antigen tests, taken a day apart). If California were to enforce this part of its guidance (will they?) I would actually be far more willing to accept the rest of the guidance's gambles. But I doubt they will, nor is it feasible given the lack of financial support to (and therefore by) healthcare institutions at this point in the pandemic.

Concluding Thoughts

Look around. Everywhere you go, people are not doing much to prevent the spread of COVID-19. It's year five of the pandemic and deaths and hospitalizations are a lot lower. I get it. Still, I wish people would mask in some situations. (Like, why not mask in super crowded spaces where nobody is talking anyway?) But it is not happening on a large scale. Nor are most people abiding by the CDC's at this point.

So, we want to find a way to maximally reduce spread -- especially to key populations -- with minimal disruption. The fever rule may help; but it could backfire if too many afebrile people now go out and spread this thing. The asymptomatic rule may turn out to be not too hazardous (though, again, I worry about the pre-symptomatics); but really, I hope infected asymptomatic people who choose not to isolate will wear N95 masks when they go out. (And for concerned readers: one-way N95 masking drastically reduces your chances of getting COVID-19.)

More than that, though, that California (and Oregon) are going rogue from the CDC's guidelines reflects something larger: Times have changed, and so should the guidelines. Yes, harm reduction is indeed a better strategy than making unrealistic requests; I get that this informed California policymakers' choices when they drew up this new protocol. But could we see the science, please?

This piece originally appeared in Faust's newsletter, .

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