At least 8% of New Brunswickers have had COVID-19, so what does that mean for immunity?

About eight per cent of New Brunswickers have had COVID-19, according to figures from the province, but the actual percentage of the population with immunity from a previous infection is likely closer to four times that, due to unreported or unconfirmed cases.

Still Health Minister Dorothy Shephard is doubling down on messaging about the importance of vaccines and booster shots.

"We know right now that when someone has COVID, we're saying that at three months, they should get their booster," she said.

"So even though there's a short-term immunity, there is also a great deal of waning immunity. And until we kind of get that science under control and we have maybe a vaccine that will last us a year, I think that we are going to be in this cycle for a little while."

An immunology expert agrees vaccination is still important, but says the province should focus on the most "vulnerable."

Michael Grant, a professor of immunology and associate dean of biomedical science at Memorial University in Newfoundland and Labrador, says that includes people who have had two or fewer vaccines and not yet been infected.

"Not that long ago they were encouraging everybody, whether they'd had COVID or not, to race out and get that third boost … as quickly as possible.

"And really, the science now indicates if you've had two shots and been infected, the third booster is not going to do very much for you," he said, referring to an observational study of close to 700,000 people age 12 and over in Quebec, released as a preprint last week and not yet peer reviewed.

More than half of school population already infected

New Brunswick has had 63,486 PCR-confirmed cases of COVID since the beginning of the pandemic, weekly COVIDWatch figures released by the province Tuesday show.

The province's current population is about 800,000, which means roughly 7.9 per cent of New Brunswickers have been infected with the virus.

Shephard confirmed the figure to reporters on Wednesday. "A good portion of our population … about eight per cent of our population has been infected with COVID."

Among certain groups, previous infection rates are much higher. More than half of the school population, for example, had been infected before March break, Shephard said.

My guess is that the actual infection rate [in New Brunswick] is … probably closer to at least 30 per cent.​- Michael Grant, professor of immunology

In some provinces, such as Ontario, official estimates now show as much as 40 per cent of the population was infected with COVID-19 since December alone.

Across Canada, recent data suggests almost half of the population has been infected.

New Brunswick Department of Health officials did not immediately respond to a request for provincial estimates.

"My guess is that the actual infection rate [in New Brunswick] is … probably closer to at least 30 per cent," said Grant.

That's what the estimate is in his province, he said, based in part on access to PCR tests being restricted to certain groups, he said.

In addition, people who test positive on rapid tests are not included. As of Tuesday, 64,238 New Brunswickers self-reported testing positive on rapid tests.

"Just from my experience here, there's a lot of people that get a positive test, they don't bother to go for a confirmatory PCR," said Grant.

There could also be people who were sick but never got tested, or were asymptomatic and never realized they were infected.

Immunity is '$100-million question'

Whether people who have had COVID are immune is the "$100-million question that we're just starting to get some really good information about now," said Grant.

"But there's a … general belief now that if you have two vaccines plus you've been infected, that you're equally immune — and in my opinion more immune — than somebody who has had three shots of the vaccine."

For people who have been infected but have no vaccines, the concern is that they may be protected against Omicron for a relatively short period of time, but it didn't boost their immunity against some of the previous strains, such as Delta, he said.

Because Omicron is a milder infection, it doesn't stimulate a really strong immunity either, said Grant, noting some people who were infected with Omicron BA1 are already getting reinfected with some of the subvariants of Omicron, although they aren't getting seriously ill, "so there is still some level of immunity."

A total of  52.1 per cent of eligible New Brunswickers are now boosted, the double-dose rate remains unchanged at 87.9 per cent, and the one-dose rate is stalled at 93.1 per cent.

Grant isn't surprised by the slowed uptake. Some people began to question the benefit of getting the third shot when they saw people who were fully vaccinated still get infected with Omicron, he said.

"The risk-benefit analysis changed for some people."

2 types of immunity

Omicron has shown reinfection is not only possible, it's "common," said Raywat Deonandan, an epidemiologist and associate professor at the University of Ottawa.

He pointed out it's unclear how many of the province's confirmed cases are reinfections.

The once sought after herd immunity, where a high enough percentage of the population is vaccinated to protect those who aren't, "might not be a thing when it comes to COVID," said Deonandan.

There might always be a portion of the population that's susceptible, he said, much like some people are susceptible to the common cold.

"Whatever immunity is earned via infection would be short-lived and not measured in years."

Vaccination plus infection offers better immunity that is "more efficacious and durable."

But experts aren't sure how long that lasts either, said Deonandan.

There are two types of immunity, he said. Humoral immunity, or antibodies, is what prevents infection and tends to wane in weeks or months. Cellular, such as T-cells, can last for years or decades, and doesn't prevent infection but does prevent hospitalization and death.

"So instead of herd immunity, we might be looking at something that some people call 'herd resistance,' where the infections continue to occur, but repeated infections mean there is enough cellular immunity that the symptoms will not be serious (except for the genuinely naive, like newborns). So there is no emergency for the health-care system," he said in an email.

"This analysis completely discounts the threat of long COVID, which is real," he added.

Long COVID has "always been on my radar," Shephard told reporters Wednesday.

A group of Moncton scientists is trying to gather as much information as possible on the symptoms, what patients need to recover and the risk factors.

"It's all still relatively new. So that data is still being collected. And we'll be working with our [regional health authority] partners and those who have a handle on long COVID to see how we need to proceed in the future," she said.

In the meantime, the communications department is working on an "aggressive campaign" to boost vaccination rates, said Shephard.

The province is able to directly contact more than 400,000 individuals who have registered for a MyHealthNB account, she said.

"I don't think we're at a point yet of making one-on-one phone calls."