Dr. Oglaza explains local infection rates among vaccinated and unvaccinated individuals

With local case rates at the highest levels Kingston, Frontenac, Lennox and Addington (KFL&A) have experienced so far during the COVID-19 pandemic, many people are wondering about the vaccination status of these daily cases.

On Friday, Nov. 19, 2021, Dr. Piotr Oglaza, Medical Officer of Health (MOH) for KFL&A Public Health addressed this question in a video posted to the KFL&A Public Health YouTube page: “Can you tell us the status of vaccinated versus unvaccinated in cases and how we calculate that?”

Dr. Oglaza began by stating, “it’s best to compare rates and I’ll explain what that means.”

He then broke down the KFL&A population into segments: vaccinated (approximately 165,000) and unvaccinated (approximately 43,000) individuals.

“We know the vaccine works really well, and is around 90 per cent effective,” he stated, explaining that 10 per cent of those vaccinated individuals would not have that full protection and they could contract the virus, thus becoming cases. “It is a high number when you look at the overall 165,000,” he said.

The entire group of unvaccinated individuals, including children for whom the vaccines are not yet available, is considered at zero per cent effectiveness, according to Dr. Oglaza. “That entire group of unvaccinated individuals is considered to be at risk for the disease,” he said.

He described, through a hypothetical scenario, how this leads to misleading comparisons when looking at daily case counts.

“So take one hypothetical day, for example,” he illustrated. “One day we had four cases among the vaccinated group. And that same day we also had five cases among the unvaccinated group, so that makes a total of nine people who are sick. And when you look at that number alone, you say, ‘oh, out of nine people, four of them are vaccinated. Five are unvaccinated.’ This is a very, very misleading comparison because that does not truly reflect the risk that vaccinated versus unvaccinated have of contracting COVID.”

Because of these misleading numbers, Dr. Oglaza said that KFL&A Public Health calculates a rate over time that better illustrates the difference in risk between the two groups, vaccinated and unvaccinated.

“When we look at these rates, we are comparing the rate of those sick among the vaccinated individuals over the total number of vaccinated individuals. And then we do that same thing for a number of sick unvaccinated and the total number of unvaccinated individuals and we have these two very different rates,” he explained.

“And when you look at these rates, we actually come up with the conclusion that you are at 5.5 times greater risk of COVID-19 if you are unvaccinated. And that’s a much more meaningful figure because it truly reflects the level of risk that these individuals face, versus those individuals who are fully immunized.”