Hospitalization of 3 COVID-19 patients reveals misunderstandings about vaccine

An epidemiologist says it's "a bit surprising" three people hospitalized in New Brunswick for COVID-19had received at least one dose of vaccine, but he and other experts maintainthe 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," saidRaywat Deonandan, an associate professor at theUniversity 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 twodoses."

Pressed for clarification on conflicting information, Department of Health spokesperson Bruce Macfarlanetold CBC Newslate 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.

Deonandansaidclinical 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 alwaysmore optimistic than real-life situations though, Deonandansaid, noting theCOVID-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 Brunswickerswho received at least one dose as of last weekor roughly 0.002 per centis about the rate he would expect, he said.

Health Canada did not respond to a request for information about any otherhospitalizations of vaccinated people across the country.

The United States has had some cases, as has the U.K.

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.

It's a message the province's chief medical officer of health has stressed since sheannouncedlast Thursday that three hospitalized COVID patients had received vaccines.

"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 COVIDis not zero."

People need to continue to follow Public Health guidelines, such as wearing a maskand 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 thinksit's "very unlikely"these hospitalizationsare due to a vaccine failure in young, healthy people.

He contendsthere'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 hospitaland what kind of people this happens to is more difficult to nail down, however.

Grant noted the vaccine studies were conducted on otherwise healthyindividuals, 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 immunosuppressiveor anti-inflammatorymedicationsto treat certain conditions at the time they receive the vaccine, the drugs can reducethe 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 chemotherapyhave 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

Deonandansaid all vaccines have a failure rate. He pointed to the annual flu vaccine, which usually has an efficacy of40 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 failureor the probability of detecting vaccine failureincreases as the prevalence of the disease increases, saidDeonandan.

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, saidDeonandan.

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 personwhom the vaccine failed to protect, half of thosetwo 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,Deonandanexpects the probability of community transmissionwill beso lowthat thevaccine failure rates will be"irrelevant."

Public Health should be able tolift protective measures one by one, and once herd immunity is achieved, he anticipates they can all be removed.

Grantencourages 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.