As researchers learn more about the Omicron variant of COVID-19, some say booster shots offer good protection against infection, but understanding how long the third dose remains effective is yet to be seen.
According to Jesse Papenburg, a pediatric infectious disease specialist and medical microbiologist in Québec, the third COVID-19 booster dose has proven effective against Omicron, particularly against hospitalizations.
But the science behind how much protection Canadians are getting with two doses versus three is a “little complex,” said Papenburg.
“Two doses offer some decent protection initially, but that protection drops off pretty dramatically and probably after three months it is pretty close to nothing … and that’s because the Omicron spike protein is different enough that it’s able to partially evade the antibodies that we produce,” said Papenburg in a Zoom interview with Global News.
Two doses or three?
Papenburg explained that the third dose helps increase people’s antibody levels in fighting infections as they start to decline.
“You see that phenomenon: soon after your first dose, we have pretty good protection against any infection, but how long will that take to wane is yet to be seen because we don’t have as many studies to look at a long-term period against Omicron infection and certainly not in Canada after the third dose,” said Papenburg.
Papenburg said data from a study done in the United Kingdom has shown a third dose of COVID vaccine has 88 per cent effectiveness against hospitalization.
An ongoing study out of Ontario first published on Jan. 1, 2022, found that seven days after a booster shot, mRNA vaccines were 93 per cent effective at protecting against the Delta variant. That number fell to 60 per cent against Omicron.
When does vaccine protection wane?
For those with two doses of a COVID-19 vaccine, researchers found after six months there was no protection against the strain that is now dominant in Canada and around the world.
“It’s unfortunate, and that’s why we need to keep using our masks and ventilation, physical distancing, all these other things that will work against Omicron,” said Jeffrey Kwong, one of the study’s leading scientists in Toronto.
Similar findings were revealed in an analysis out of the United States last week. Researchers at Kaiser Permanente in California found vaccine efficacy for two doses was virtually nothing after just three months.
The silver lining is what they didn’t see — not a single booster recipient ended up in hospital.
Vaccines protect from hospitalization
“It’s not like 100 per cent guaranteed you won’t end up in hospital, but it really significantly reduces that chance. But as more and more people are discovering, it doesn’t mean you’re not going to get COVID,” said Martha Fulford, an infectious disease specialist in Toronto, who read the U.S.-based study.
She also said if a person does get the virus, they will gain natural immunity for a period of time.
According to Kwong, anyone who has not yet contracted coronavirus should be first in line to get a booster, ahead of those who have already had a case of COVID-19.
“I think given that there’s a lot of people out there who haven’t been infected and need boosters … I think we should prioritize those folks first.
“The natural protection that you’ve got against Omicron is more specific against Omicron, and these vaccines are less specific against Omicron,” said Kwong.
Papenburg went on to explain that if the person got infected with COVID-19 in mid-December when Omicron was becoming the dominant strain in Canada, then they would probably have immunity against it for at least two months or perhaps longer.
“If you had an Omicron infection, you shouldn’t get a booster until at least two months have passed or longer…it’s (a matter of getting the booster shot) when your antibody levels have started to decline. You don’t need to boost once your antibody levels are high and protective,” he added.
Do we need yearly boosters?
As to whether people will need more booster doses in the future, Papenburg said vaccine researchers expect there will be a need to have yearly COVID-19 shots, similar to the way Canada runs annual influenza vaccine campaigns.
“This will happen for two reasons. One is the phenomenon that there is an element of waning immunity to the vaccines in the same way that we see with influenza vaccines,” he said.
The other reason is that viruses change over time.
READ MORE: Omicron and living with COVID — Why the new variant might change the timeline
“We’ve seen it with influenza year in, year out. We have to adjust which strains we include in the seasonal influenza vaccine … probably we’re going to see that with COVID-19 as well, where we try and predict what is going to be the dominant strain and produce a vaccine that is against that strain,” Papenburg said.
In the meantime, vaccine manufacturers are working to make improvements and developing shots to target certain strains.
As of late last year, Novavax Inc. said it had started working on a version of its COVID-19 vaccine to target the Omicron variant.
Other vaccine developers, including Germany’s BioNTech SE and Johnson & Johnson, have also said they are testing the effectiveness of their shots against the new variant.
— with files from Jamie Mauracher