Tag Archives: asymptomatic Covid

Herd immunity, sterilizing immunity, and the current best guesses

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Britain is now the proud operator of several mass vaccination centers, with more promised shortly, and general practitioners are scheduling their oldest patients for vaccination. But that doesn’t mean we’re out of trouble. The number of hospital cases is still rising and there’s talk of the current lockdown not being tight enough.

And we just approved a third vaccine, Moderna’s. Not long ago, Boris Johnson was crowing at Scotland (which on average isn’t happy about having left the European Union) that if they’d stayed in the EU they wouldn’t have gotten vaccines so quickly. So it’s a nice little piece of irony to read that, approved or not, we won’t get or hands on this third vaccine until April because we’ve left the European Union.

I know I shouldn’t think that’s funny, but I can’t help myself.

 

Irrelevant photo: heather

Are we close to herd immunity?

The latest statistical modeling says one in five people in England may have already had Covid. How did they come up with that number? Since the official statistics inevitably underestimate the number of infections (a big chunk of people don’t get sick but carry the disease without knowing it or showing up in the statistics) and since the track and trace system is widely recognized as being roughly as useless as it is expensive, they get their statistics by comparing the number of deaths in an area to the estimated infection rate, putting them in a blender with a few other number and a dash of cinnamon, then baking at 160 C. for fifty minutes. 

In some areas, they estimate that one person in two has had the disease. The number of infected people may be up to five times higher than the number on the test and trace books.

Is that herd immunity? 

Nope. Exactly how many people would have to have had the bug to create herd immunity is still unknown, but a computational biologist estimates that 70% of the population will need to be vaccinated to stop the pandemic in the US. But that only applies to the US; it’s not a fixed number. People behave differently in different places, which upsets the numbers–they’re touchy little beasts–so they arrange themselves into different patterns. 

The number also depends on how long immunity lasts–no one knows yet–and on whether the vaccine turns out to keep people from passing on the infection. 

Most of our commonly used vaccines prevent severe illness but don’t give us what’s called sterilizing immunity. In other words, they keep us from getting sick–or at least from getting very sick–but they don’t kill off every bit of the disease that’s running around inside us. 

On the positive side, having less of the disease circulating inside our complicated little innards may (notice how much wiggle room I’ve left myself there) mean we pass on a milder form of the disease if we do give it to someone else.

An experiment with a chicken virus and a flock that was half vaccinated found that the unvaccinated birds came down with a milder disease than if the whole flock had been left unvaccinated. So even if the current vaccines don’t give us sterilizing immunity, Covid may yet follow that pattern and become milder once a significant portion of our flock has been vaccinated.

May. No one’s offering us a guarantee.

And no, none of the vaccines currently in use will cause us to grow feathers.

 

Transmission and hospitalization

In Britain, the current crop of hospitalized Covid patients are younger than they were during the first peak of the virus. People under 65 now make up 39% of hospital admissions. In March that was 36%. It’s not a huge change, but it is a change, and it’s worth noticing. 

The best guess is that the over 65s are more likely to be out of circulation. We left the party early and are tucked up in our little beds just now. That makes us less likely to become infected and less likely to show up in either the hospital or the statistics. But so much emphasis has been put on the elderly being vulnerable that we tend to think the non-elderly are made of steel.

They’re not. They can get very sick from this thing. In particular, pregnant women seem to be more vulnerable than non-pregnant women (or non-pregnant men, for that matter) in their age groups. 

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Half of all Covid transmissions come from people with no symptoms, including from people who never do develop symptoms. 

What does that mean in practice? That every one of us needs to act as if we could be carrying it. And that we need to look at our friends and family and neighbors as if they could be carrying it. That we need to look at other human beings and think, Oooh, yuck, germs! 

That’s not, I admit, a policy recommendation. It’s not even a real recommendation. It’s just an observation on how much it goes against the grain to live this way.

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A study reports that Covid can still be transmitted after seven days. Or after ten days. After ten days, 76% of the people tested still had detectable levels and 86% did after seven. 

So recommending a shorter period of isolation is a gamble. On the one hand, the theory goes that people are more likely to actually isolate themselves if you demand a shorter time. On the other hand, they can still be shedding the virus at the end of it.

The problem is not only that some people are jerks and don’t put the safety of others first. The larger problem is that a lot of people can’t afford to miss a day’s work–they’re living on the edge as it is. So when mass testing’s offered, they don’t show up because they can’t afford to be told to stay home. If they do end up getting tested and are positive, they stagger to work for as long as they can anyway. Because the hounds of hell are nipping at their heels. 

Already 70,000 households have become homeless during the pandemic and some 200,000 are teetering on the edge. There’s money available to people who have to self-isolate, but not to everyone and it’s not enough to cover the bills anyway. 

And if that doesn’t hold your attention, some people are still being told they’ll be fired if they don’t come to work.

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On a happier note, my partner’s been scheduled for her first vaccination. If all goes well (stop laughing–it could) I should be in line in mid-February. 

How to turn a Covid cluster into an outbreak

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Until recently, the part of Britain I live in had very few Covid cases. Now we have a cluster of them. Isn’t progress wonderful? It’s not a huge cluster, but then no outbreak starts out huge. It scares the antibodies out of me.

So how’s it being handled?

The nearby secondary school sent one whole year group home when I’m not sure how many kids tested positive. Following government guidelines, they treat each year group as a bubble, having them enter through different doors and eat at different times and keeping them as physically separate as possible. The theory is that if the outbreak’s in one year group, the others should be safe.

You can believe that if you like.

And after school, as my neighbor reminds me, they go home. Her kids are in different bubbles in school–a primary school, but the reality’s the same. The minute they get home, they jump on each other, wrestle their way across the living room floor, and hold a germ exchange.

Only she didn’t call it the living room. That’s American. She also didn’t say anything about a germ exchange.

Irrelevant photo: St. John’s wort, getting ready to bloom, but not at this time of year. 

The point, though, is that the bubbles leak–probably at school and definitely at home. And bubbles that leak aren’t bubbles. They’re something else. Cups, maybe. Things with sides and a bottom but no top because that’s how you pour the tea into yourself. 

Or not the tea, the germs.

When the school didn’t have enough teachers to keep going, it sent everybody home to keep up with their lessons online. At least, those who have internet access. 

Don’t get me started. You know what I’ll say.

Some of the kids were told to self-isolate–probably the ones who’d shared a leaky bubble with someone who was known to have the virus. Their families, though, were told they didn’t have to to self-isolate unless their kid became symptomatic. 

How are kids who share a bedroom supposed to self-isolate? Well, you take masking tape and make a line down the middle of the room, and you tell the germs, in the tone of voice you use when the kids have gotten into  your secret stash of chocolate, to stay on their own side.

One of the many problems with all this is that people are infectious before they become symptomatic. Some people never become symptomatic and they’re infectious anyway. And people are even more infectious if they live in a country led by an incompetent, corrupt government. I can’t explain that medically, but it does happen.

Back to the school, though: No one wants to tell all the students’ families, or even just the families with kids in that first infected age group, to go into quarantine. Because that’s be a lot of people. 

Which is why I worry we’ll be looking at a bigger local flareup soon. 

Meanwhile, the county government reminds us to wash our hands and maintain social distancing. Which is better than climbing into each other’s pockets and poking our heads out once a day to ask if the pandemic’s over but doesn’t take into account what it’s like to share a house or apartment or a life with actual human beings. We breathe the same air. It goes into our lungs and it goes out. If someone has the virus, the odds are good that everyone will trade it. It’s always looking for new lungs to explore and conquer, no matter how clean our hands are.

On the other hand, clean hands are very nice things to have.

No one knows for sure where our cluster of cases started, but someone told me today that it traces back to a kid who came home from university. His parents wandered all over town with no idea that they’d been infected and his mother’s sure she infected half of Bude and feels terrible about it. 

Whether she’s right or not doesn’t matter, really. It does remind us–or it should–that we don’t know if we’re infectious so we all need to act as if we are. Because we can feel great and still make people around us sick. 

And it’s yet another reminder that this lockdown has as many holes in it as the school bubbles. 

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A third vaccine, the Oxford Astra-Zeneca vaccine, has reported its accuracy level: It’s 62% but could go up to 90% if the first shot uses a lower dose. (No, I can’t explain it either.) It’s also cheaper than the first two and can be stored in an average refrigerator, and Astra-Zeneca has said it will forgo any profit on it.

Even before that was announced, though, the health secretary told us that if approval comes in time the National Health Service would start vaccinating people before Christmas. Initially, family doctors will immunize the most vulnerable, and NHS staff will be vaccinated at work. Mass vaccination centers will be set up. 

That sounds startlingly as if someone somewhere had an actual plan, but the grapevine tells me that the local doctors’ office hasn’t been contacted about this. They have only the vaguest idea how it will work and what they’re supposed to do or how.  

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Preliminary studies indicate that mouthwashes containing cetylpyridinium chloride (CPC to its friends) can, under laboratory conditions, kill the coronavirus in thirty seconds. But as Donald Trump so famously informed us, so can bleach. So can nuclear weapons, although that hasn’t been verified in a lab. You know what scientists are like about setting off nuclear weapons in their labs. The few who’ve done it have had problems reconstructing their notes. 

A darning needle could also, at least potentially, kill the virus, but viruses are small and stabbing them isn’t easy, as the human immune system has found to its cost.

Don’t think about that too hard. I do understand that the human immune system doesn’t come equipped with darning needles. Let’s call it a metaphor and move on quickly.

With all of this, the problem is what you do with the information. How do you get your chosen virus-o-cide and the virus to meet in the right situation? Take mouthwash: Do you pinch the virus between two fingers and dunk it in the mouthwash? Do you spend your day with a mouthful of the mouthwash and hope that anything you breathe in decides to go for a swim? This isn’t going to be simple.

As you may have figured out, I am–and the world is in my debt for this–not a scientist. Someone may yet find a use for mouthwash in humanity’s fightback against this invisible predator. It’s safe, it’s available, and as medical interventions go it’s cheap.

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Finally, a piece non-Covid news: Donald Trump’s lawyers filed a lawsuit in a Michigan court claiming that Democratic-leaning parts of Michigan had suspiciously high voter turnouts. This was all supposed to link back to voting machines and computer programs and Hugo Chavez. 

And to prove they’d done their research carefully, they listed a number of localities in Minnesota instead of Michigan.

Chavez probably moved them before the election for this very purpose. If he wasn’t already dead by then.