With limited testing, how do we know we've passed Omicron's peak?

Even though Public Health is only keeping track of a fraction of Nova Scotia's COVID-19 cases, the province's chief medical officer of healthsays this kind of "surveillance" testing strategy can tell us a lot about the Omicron wave.

The province estimates there are more than4,200 known active cases of the coronavirus right now, but that's only based on positive lab-based PCR tests.Dr. Robert Strang said his team is also working toget a better estimate of the total cases, which would include rapid tests.

Over the last couple of months there's likely been between 3,000 and 5,000 people a day infected by COVID, hetold CBC Radio's Information Morning on Thursday.

"Not to diminish those deaths, but the number of people that are hospitalized and ending up dying is very small, given the total number of cases," he said.

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Strangadded that given how much Omicron has spread,"there's enough hospitalization that it'sputting significantpressure on our health-care system."

His conversation withhost Portia Clark has been edited for clarity and length.

How difficult is it to estimate how many Nova Scotians have contracted COVID-19, and are still contracting it, given where we are with testing?

To actually estimate the number of people who have been infected we'll never get a completely accurate picture but we've asked our epidemiologic team to look at this, looking at vaccination rates, hospitalization rates, our rates of ourlab testing, and we can do some estimates on that.

The other point is that we know that we have a good understanding of where we are in terms of the wave with our PCR lab testing because we're getting several thousand people tested a day. That is certainly enough testing to give us an accurate picture of where we are at in the wave, and we know from that PCR lab testing, we are past the peak of the spread of Omicron in Nova Scotia.

This week is the week where, if things go as we expect, that we're right in the middle of the peak of hospitalizations.

We're on the downward trend, but we also know that hospitalizations usually lag two to three weeks from your case surveillance information. So this week is the week where, if things go as we expect, that we're right in the middle of the peak of hospitalizations now and then we should soon start to see those trend downward as well.

Why are you confident that you can base these estimates just around PCR tests?

We have a large enough volume, several thousand people a day testing with PCR, and so that is enough testing from a surveillance perspective. You don't need to know about every case, but you need to do enough testing, in enough parts of the population, so you can get an accurate estimate and we do that.

It's similar to what we do with flu every year, and we actually do a lot less testing for flu, but we still have a very accurate picture of the wave of flu that happens every year. So we're very comfortable with the amount of testing and what we're seeing and where we are on the Omicron wave.

How worried are you about this new sub-variant, the BA.2?

The original Omicron we're seeing is BA.1 and thisjust has some changes, it's like a cousin so it's BA.2.At the office we've been calling it a baby. Omicron had a baby, so we don't yet know how different it is and whether those differences have any implications for how it might behave.

We have to watch and understand as the science evolves. The reality is, is this goes on all the time with respiratory viruses, and we just now have the sophisticated laboratory capacity and research capacity to detect all of these variations.... Most of these variants don't actually have any implications in terms of a virus that may behave very differently, but some of them do so we have to watch it very carefully and we'll adjust if we need to.

I can't even imagine thinking ... of the devastation Omicron would have created if it had happened before we had vaccines.

People may be getting vaccine fatigue, questioning why they bothered to get vaccinated and boosted if they're going to get sick anyway. What do you want people to know about that?

At an individual level, certainly being vaccinated has protected you from getting more severely ill, for most people. That's critically important that the vaccines, even two doses of the current vaccines, are good at protecting against severe illnessand, collectively, they've been critically important.

If we didn't have the high levels of vaccine coverage that we have achieved over the last year in Nova Scotia, we would be in a much more challenging situation. I can't even imagine thinking of what the devastation Omicron would have created if it had happened before we had vaccines.

And even if people are infected, we know that the immunity they get from infection is short term it's probably in the range of about three months or 90 days. And vaccines, getting your first, second or your booster dose, remain critically important, even if you've been infected, to produce longer-term immunity.