Hospitalization of 3 COVID-19 patients reveals misunderstandings about vaccine
Vaccines are not 'bulletproof vests,' says University of Ottawa epidemiologist Raywat Deonandan
An epidemiologist says it's "a bit surprising" three people hospitalized in New Brunswick for COVID-19 had received at least one dose of vaccine, but he and other experts maintain the probability of "anything bad" happening to people once they've been vaccinated is "vanishingly small, but not zero."
"That's your take-away message — this is all about probability, not certainties," said Raywat Deonandan, an associate professor at the University of Ottawa.
"That's not a comforting answer, but that's the answer."
Last Saturday, during the COVID-19 briefing, the province's chief medical officer of health told reporters one of the hospitalized patients had been "fully vaccinated with two doses."
Pressed for clarification on conflicting information, Department of Health spokesperson Bruce Macfarlane told CBC News late Tuesday that 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.
It takes two to three weeks for the vaccine to take effect and for the person to build up immunity.
"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.
Deonandan said clinical trials and efficacy scores showed some vaccinated people still got sick, but "what is a bit surprising is that these were hospitalized cases."
"The clinical trials showed us that the vaccines had a 100 per cent chance of keeping vaccinated people out of the hospital."
3 represent 0.002%
Clinical trial numbers are always more optimistic than real-life situations though, Deonandan 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," he said.
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.
Health Canada did not respond to a request for information about any other hospitalizations of vaccinated people across the country.
Deonandan anticipates a "vanishingly small number" of vaccinated people may also eventually die from COVID-19.
"What we have done a poor job of explaining is vaccines are not bulletproof vests," he said. 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.
"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," Dr. Jennifer Russell told CBC News on Friday. "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.
No information about the three patients or which vaccine they received has been released.
'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 hospitalizations are due to a vaccine failure in young, healthy people.
He contends there's "very little evidence anywhere" 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.
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.
If the prevalence is low, those individuals for whom the vaccine did not work, "will never know," he said.
"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."
Public Health should be able to lift protective measures one by one, and once herd immunity is achieved, he anticipates they can all be removed.
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.
- The headline on this story was changed to better reflect the overall information in the story. A previous version of the story indicated, based on incorrect information previously provided by the chief medical officer of health, that one of the hospitalized patients had received both doses of the vaccine more than 14 days prior to the onset of symptoms. In fact, the second dose was received less than seven days prior to symptom onset and, Public Health said later, would not have been considered active yet.Apr 13, 2021 7:27 PM AT
With files from Information Morning Saint John