Thread by @EpiEllie

Last week, the BC CDC posted a pre-print estimating past COVID infections in Vancouver & southern BC.

This study is a testament to the successful pre-omicron prevention efforts of the BC covid team and a damning indictment of the failed response to omicron & sub-variants.

A 🧵

WHERE: This study uses data from the area around Vancouver & southern BC in Canada.

This is where I (mostly) grew up and my family and friends are there, so you bet I dug into this paper deeply!

Full disclosure: I was also a paid consultant at BCCDC and at VCH back in 2010/11

LOCAL CONTEXT: Health care in Canada is universal single-payer.

All the doctors & nurses & hospitals are part of the government healthcare system, so there’s less of an issue with uninsured people unable to access care.

That also means these data basically cover *everyone*.

WHAT: The BCCDC team got “residual sera” from the (only) outpatient lab testing company, with 100 or 200 samples in each of 8 sample periods (each ~2 weeks long).

This figure shows when the sampling happened (pink bars)

WAIT, WHAT’S RESIDUAL SERA?

Basically, it’s leftover blood samples from people who have gotten blood drawn at a doctors visit for pretty much any reason.

So, these are not samples taken for this study specifically, and they aren’t from people who think they might have covid.

WHATS IN THE BLOOD?

I’m no immunologist but briefly, when we get infected we make antibodies to multiple bits of the virus. The vaccine only has one of those bits.

By testing your antibodies, we can tell if you’ve been infected at all, or if you had a vaccine but no infection.

SELECTION, BUT IS IT BIASED?
Who has blood taken:
•pre/non-covid health complaint
•post-covid health complaint
•annual check up

Some of these people will take extra precautions, but others are more likely to have covid.

It’s a subjective call but IMO this sampling is ok👍🏼

SUCCESSFUL COVID CONTROL:

For the first 6 sampling times, the data the BCCDC reports look great!

The gray bars are percent with any antibodies. The darkest part is those with all the antibodies, and the lighter part is vaccine antibodies only (so no infection).

Let’s read this graph together:

In 2020-Jan 21, less than 5% of people had any immunity to COVID.

By June 2021, 10% of people had evidence of infection but another 46% had evidence of vaccine protection (total: 56%). By Oct 2021, the vaccine number was up to 74% (total: 83%)

Now, 10% of the population showing evidence of infection with a novel pathogen might seem a bit alarming in the abstract, but remember thats an estimate of all infections over 22 months, not all at once!

That’s pretty commendable infection control and highlights how well BC’s early covid response worked.

The overall vaccination estimate of ~74% is also very good if we remember that in Sept/Oct 2021 the kids vaccine was only newly available.

FAILED COVID CONTROL:

But then things take a turn worse.

In Nov/Dec 2021, like so many of our leaders worldwide, BC looked at the incoming data on the new variant of concern, omicron, and threw up their hands in defeat.

The data show clearly how much damage this did.

This is the second half of the graph.

Now, we see that in March 2022, the percent of people with evidence of infection jumps hugely! From 10% to 42%, i.e. 32% of people newly infected!

In 6 months *3 times* as many people were infected as in the *entire* previous 22 ‘months

MORE FAILED COVID CONTROL: clearly the initial omicron surge was a disaster in BC. One third of the population infected in a 6 month period.

Even if the worst that happened was needing a week off work, that was a massive unexpected blow to the economy.

Normally, we expect disasters to be followed by recovery. But not this time.

Precautions were kept off, and over the next 4-5 months, an *additional* 20% of British Columbians were infected with COVID.

BUT, BUT, BUT…

Some of you are thinking this can’t be true, because the summer epi-curve doesnt show another huge peak in reported cases.

But, these data are incomplete. Omicron crashed BC’s testing system. The authors estimate they now miss 91 cases for every 1 reported!

WISHFUL THINKING

So far, this paper, while demonstrating a horrific burden of COVID in BC this past year, has been well documented, and the science is well done, and transparently reported.

Then we get to the discussion & the wishful thinking starts.

The authors summarize their findings as if this data showed a resounding success.

They praise the response (that they were part of leading) for getting immunity levels up to 95-98%. And they celebrate the high infection rates.

Now, 98% immunity *would* be great if covid were a one-and-done infection.

But it isn’t. As we can clearly see from the authors’ own data, people who are vaccinated can still subsequently get covid. But the authors data *cannot* tell us anything about reinfection.

There are 3 problems:

First, the authors’ data does not tell us about *every infection*. It just tells us about the percent of people *ever* infected!

There could be (maybe many) more infections if re-infections happen.

We know they do. These data dont tell us how often.

Second, covid kills people, and people who are dead by definition cant get reinfected.

So, even if we had person-level data, we couldn’t just compare infections among vaccinated with re-infections.

That comparison will always be biased.

Third, covid also ***makes people sick***

It is a foolish idea to use infection as a way of developing antibodies.

Infection makes you sick! Maybe you feel gross for a week. Maybe you struggle to breath for a year. Maybe you die. We cant predict which!

BOTTOM LINE:

Until Fall 2021, BC CDC was taking covid seriously and protecting their community from the pandemic. But now they have failed.

They need to admit that and start planning for what comes next. Definitely more chronic disease, but more infections or not is a choice.

Another very good discussion of the paper here 👇🏼

https://twitter.com/furnesscolin/status/1570929052906852352

Study link here: medrxiv.org/content/10.110…