An epidemiologist says it's "a bit surprising" three people hospitalized in New Brunswick for COVID-19 had been vaccinated, including someone who had two doses before the onset of symptoms. Raywat Deonandan, an associate professor at the University of Ottawa, says the clinical trials showed some vaccinated people still got sick, but that the vaccines "had a 100 per cent chance of keeping vaccinated people out of the hospital." But clinical trial numbers are always more optimistic than real-life situations, he said, noting the COVID-19 vaccines were tested on only tens of thousands of people, and now they're being distributed to tens of millions of people globally. So some hospitalizations were "bound to happen eventually," said Deonandan. Three hospitalizations out of the more than 120,000 adult New Brunswickers who received at least one dose as of last week — or roughly 0.002 per cent — is about the rate he would expect, he said. Deonandan anticipates a "vanishingly small number" of vaccinated people may also eventually die from COVID-19. "This is all about probability, not certainties," he said. "What we have done a poor job of explaining is vaccines are not bulletproof vests." They're merely a mitigation tool. And until we achieve so-called herd immunity, with between 70 and 90 per cent of the population inoculated to protect others who aren't immunized, they're the best one we've got. "The message is, if you get vaccinated, your probability of anything bad happening to you, COVID-related, is now vanishingly small, but not zero." Have a question or something to say? CBC News is live in the comments now. Dr. Jennifer Russell, the province's chief medical officer of health, said the risk of hospitalization, ICU admission and death from COVID-19 are greatly reduced by the vaccine, but all New Brunswickers will continue to be at risk until around June 15, when the province hopes to have everybody vaccinated with one dose.(Government of New Brunswick) It's a message the province's chief medical officer of health has stressed in recent days since she took many people by surprise by announcing last Thursday that three hospitalized COVID patients were vaccinated. It takes two to three weeks for the vaccine to take effect and for the person to build up immunity, Dr. Jennifer Russell had said. "I don't want people to get a false sense of security that they're immune to COVID-19 once they've had a vaccine," she told CBC News on Friday. "And even after two doses of vaccine, we know that the risk of getting COVID is not zero." People need to continue to follow Public Health guidelines, such as wearing a mask and physical distancing, even if they've been vaccinated, she said. On Saturday, when CBC News asked how many of the hospitalized patients had been fully vaccinated, Russell confirmed the even more surprising news that one person had received both doses. On Tuesday, pressed for clarification on conflicting information, Department of Health spokesperson Bruce Macfarlane said the person received the first dose more than 14 days before the onset of symptoms, but the second shot was less than seven days prior to symptom onset. "In this case the second dose is not considered active yet, so the person still has the equivalent of one dose protection," Macfarlane said in an email. The other two people had received a single dose each — one of them more than 14 days before symptom onset and the other, less than 14 days prior, he said. 'Very unlikely' 3 are young, healthy Michael Grant, a professor of immunology and associate dean of biomedical science at Memorial University in St. John's, acknowledged it's "a concern" people are still being hospitalized when the vaccine rollout is underway. And it comes when there's already "skepticism" about vaccines, he said. "It's been a bit of a public relations nightmare with the AstraZeneca vaccine, with what would appear to be a bit of flip-flopping as better information becomes available." But Grant thinks it's "very unlikely" these cases are due to a vaccine failure in young, healthy people. He contends there's "very little evidence anywhere else" that people who have been fully vaccinated and developed immunity from that vaccination are at risk for severe infection. "So unless there's something very peculiar occurring in New Brunswick, I don't think there should be any sort of generalization that people can be fully vaccinated, develop a good immune response and still be at risk for severe illness," said Grant. Dr. Michael Grant, a professor of immunology at Memorial University in St. John's, said it's been a 'hard psychological blow' for the population to be told once everybody's had the vaccine, we can start to go back to to a normal life, and then to hear some restrictions may have to remain in place even after most people have been vaccinated. (CBC) Why some vaccinated people are ending up in hospital and what kind of people this happens to is more difficult to nail down, however. Grant noted the vaccine studies were conducted on otherwise healthy individuals, so it's still too soon to know how some groups of people will respond. But there is some evidence that older people do not respond as well to the vaccine, so they may remain "somewhat susceptible" to the coronavirus, he said. If people are taking immunosuppressive or anti-inflammatory medications to treat certain conditions at the time they receive the vaccine, the drugs can reduce the response they make against the vaccine, said Grant. A couple of studies with cancer survivors who are on some form of maintenance therapy or whose immune system hasn't recovered from chemotherapy have shown they respond "very poorly" to one dose of the vaccine. "And there will be very, very rare cases where people do make an immune response against the vaccine and still get infected with the virus somehow and develop illness," he said. No vaccine's perfect Deonandan said all vaccines have a failure rate. He pointed to the annual flu vaccine, which usually has an efficacy of 40 to 70 per cent. "And yet we never complained when we got the flu vaccine and saw hey, some people got the flu," he said. "But, you know, people aren't afraid of the flu because we don't hear about the thousands who die every year of the flu." The probability of vaccine failure — or the probability of detecting vaccine failure — increases as the prevalence of the disease increases, said Deonandan. Every vaccinated person still has a very small chance of transmitting and getting the disease. This may increase with the highly transmissible COVID variants, including the two now confirmed in New Brunswick — the variant first reported in the U.K. and the variant first detected in South Africa. But they have to be exposed to the disease first. Their chance of being exposed varies with the prevalence of the disease in the community. So if the prevalence is high, then the risk of exposure is high. "So this is all a population game. This is getting sufficient immunity into a sufficient number of people with the understanding that not everybody is going to be perfectly immune." Interpret numbers carefully How we interpret and communicate the numbers is important, said Deonandan. He offered as an example a high school of 100 people, where 99 of them are vaccinated against the measles with a vaccine that has a one per cent failure rate. If an outbreak infects the one person who didn't get vaccinated and the one person whom the vaccine failed to protect, half of those two people were vaccinated. "So you could look at that statistic and say, 'Oh, my God, I've got a 50-50 chance of getting measles if I got vaccinated," he said. But that's incorrect. "You have a one per cent chance of getting measles if you got vaccinated. So it depends on how you view the numbers. This is really important." A couple of months after more than half the population has been immunized, Deonandan expects the probability of community transmission will be so low that the vaccine failure rates will be "irrelevant." Grant encourages people to continue to get immunized. "The vast majority of cases, there's very strong evidence that having the vaccine is going to protect you against developing severe illness," he said. Have questions about this story? We're answering as many as we can in the comments.