Why experts say booster shots are still critical, even if vaccine policies are relaxed

With some provinces taking steps to end proof of vaccination policies and COVID-19 infections hitting record numbers during the Omicron wave even among the vaccinated, experts say vaccines and booster shots still remain a critically important tool against the pandemic.

Saskatchewan ended its proof of vaccination policy on Monday, after Premier Scott Moe controversially said vaccines were not reducing transmission, a claim disputed and criticized by medical experts. Ontario also announced on Monday it would be accelerating its reopening plans, lifting vaccine requirements for all non-essential businesses on March 1 should “public health and health system indicators continue to improve.”

While scientists are still learning about the highly infectious Omicron variant, there is strong data that suggests getting a third shot of a COVID-19 vaccine helps curtail the overall transmission and severity of infections. What is less clear is what happens when someone is boosted and becomes infected.

“Three doses may prevent more infection than two doses and if you're not infected, you can't transmit,” Dr. Zain Chagla, an associate professor at McMaster University and co-medical director of infection control at St. Joseph’s Healthcare Hamilton, said in a phone interview.

In other words, the odds of becoming infected with COVID-19 when an individual is triple-vaccinated are lower compared to someone who is not. While protection against Omicron is not nearly as robust compared to previous variants, experts say it does not mean there is no protection at all.

Even if Omicron evades vaccine protection more often compared with the Delta or Alpha variants, having more layers of protection is better when we are in the midst of a surge, says Chagla, especially for those who interact with vulnerable people.

For Omicron, the protection with a third vaccine dose starts at 60 per cent and drops to about 40 per cent after about 15 weeks, according to Chagla, citing recent studies.

“The people that are vaccinated with three doses may have some more protection against getting infected than people with two doses or no doses,” he said.

More than 84 per cent of Canada’s eligible population have had their first two doses, according to the CTVNews.ca vaccine tracker. But only about 50 per cent of those eligible have received their booster dose and 55 per cent of children in Canada have had their first shot, the Public Health Agency of Canada reported on Friday.

Some clinical trial results show that the third dose makes a substantial difference compared to just two doses in terms of reducing actual infection and three studies published by the CDC in January found that boosters helped keep patients from being hospitalized.

“With the virus less likely to penetrate and set up its nest and start growing, by pure logic, its capacity to emerge from that and shed more viruses is reduced as well,” Dr. Ciriaco Piccirillo, an immunologist and professor at McGill University, said in a phone interview, adding that the sequential doses of vaccines are like a bucket of water on fire that helps keep the virus at bay.

“The capacity of the individual to transmit is reduced compared to the unvaccinated…the vaccinated individual at multiple levels is far more resistant, far less likely at developing disease, particularly more severe disease.”

If someone is fully vaccinated, even if the virus manages to get into the respiratory tract and into the cells, Piccirillo said, that virus will not evolve into greater, more severe forms.

Still, preliminary research is mixed on whether the viral load for an individual vaccinated and infected is similar to someone infected after two doses or none at all.

“The data around whether or not, when you do become infected, are you less likely to transmit -- it's not very clear with Omicron,” said Chagla, noting a recent, small pre-print study out of Spain that was not yet peer-reviewed suggesting the viral load of someone infected with Omicron was the same regardless of vaccination status.

Meanwhile, a Danish pre-print found that the BA.2 subvariant, while more contagious, appeared to have a higher transmission rate among the unvaccinated compared to the BA.1 Omicron variant, with boosted and fully vaccinated individuals less likely to get infected and transmit compared to the unvaccinated.

Another peer-reviewed study published last month also suggested that the infectiousness in breakthrough cases was similar to those who were unvaccinated.

NOT A SIGN OF VACCINE FAILURE

But there are other reasons why experts continue to encourage being up to date on vaccinations: the virus is programmed for survival, so it will continue to try to evolve to become more “stealth-like” and to circumvent our immune blockade.

Global health experts and agencies including the World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) have all stated that the more people are vaccinated, the fewer opportunities for the virus to circulate, which in turn, leads to fewer opportunities for mutations to occur. The vaccines themselves do not cause variants.

“It’s not a measure of vaccine failure simply because the overwhelming numbers worldwide – and locally – clearly demonstrate if you are fully vaccinated and of the general population of healthy people, you're not going to be in the hospital,” Piccirillo said.

The reduction in severe disease is among the most important reasons why health officials say boosters – which restore more protection against Omicron – are important. Not only does it help prevent infected people from becoming seriously ill, it also helps reduce the strain on the health-care system so that hospitals also have the capacity to care for other non-COVID-19 patients, such as those with cancer.

People who are boosted are at incredibly low risk of dying or being hospitalized because of COVID-19, said Chagla.

“Certainly in groups like those over the age of 50, those with underlying medical conditions, that seems to be persistent and fairly powerful protection against severe disease.”

The vaccines have never been 100 per cent fool-proof, however, making it important for healthy people to get vaccinated and protect those around them who may be vulnerable, medical experts say.

Hospitalization data from the Omicron wave shows that those who are hospitalized tend to fall into three categories, says Piccirillo.

“If you take a look at the hospitals right now, unequivocally, the vaccinated people who find their way to a hospital all have pre-existing conditions, or are elderly,” he says. The general population of healthy people who end up hospitalized because of COVID-19 is because they are unvaccinated.

“The numbers clearly point to that connection.”

DOING THE MATH CORRECTLY

While the “raw” data makes it seem like more vaccinated people are being hospitalized, experts explain that those numbers must be taken in context of the greater population. If 10 people are hospitalized, with half of them vaccinated and the other half unvaccinated, those figures need to account for the overall vaccination rate of the population. So if 90 people are vaccinated in a population of 100, that means there are five vaccinated people out of 90, or 5.5 per cent, who end up hospitalized, and five unvaccinated people out of 10, or 50 per cent, who end up hospitalized.

It is also important to distinguish those who are hospitalized for other reasons and tested positive for COVID-19 from those who are hospitalized specifically for COVID-19, Piccirillo added, because the patients in the former category are not there to be treated for respiratory distress, demonstrating the vaccines are doing what they are meant to do.

“If you are sufficiently vaccinated…your chances of infection are significantly diminished,” said Piccirillo. That in turn reduces that chance of you spreading to a loved one who has cancer or is immunocompromised in other ways, he said.

Research indicates that getting infected after having already been vaccinated could give an individual “super immunity” against the virus, but some people hesitant about getting the vaccine at all say immunity through infection is better. Experts say that is a very risky way to gain immunity with no guarantee it will not result in hospitalization, debilitating long COVID, or even death, as was the case of a Czech folk singer who died after deliberately contracting the disease.

“I know of perfectly fit people who’ve died unvaccinated, so I wouldn't take that Russian Roulette gamble,” said Piccirillo.