Data analysis links Omicron to less severe disease, shows variant is better at evading vaccines
South African analysis shows Pfizer jabs protect 70% against hospitalization from omicron
The omicron variant appears to cause less severe disease than previous versions of the coronavirus, and the Pfizer vaccine seems to offer less defence against infection from it but still good protection from hospitalization, according to an analysis of data from South Africa, where the new variant is driving a surge in infections.
While the findings released Tuesday are preliminary and have not been peer-reviewed — the gold standard in scientific research — they line up with other early data about omicron's behaviour, including that it seems to be more easily transmitted.
A two-dose Pfizer-BioNTech vaccination appeared to provide just 33 per cent protection against infection during South Africa's current omicron wave, but 70 per cent protection against hospitalization, according to the analysis conducted by Discovery Health, South Africa's largest private health insurer, and the South African Medical Research Council.
The data was gathered from Nov. 15 to Dec. 7, during which time omicron was first spotted by scientists in South Africa and Botswana, and may change as time passes.
Researchers around the world are rushing to figure out what omicron will mean for the coronavirus pandemic, now well into its second year.
Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organization (VIDO) at the University of Saskatchewan, said the early analysis from South Africa around vaccine protection is promising.
"The 70 per cent protection against severe disease is really encouraging and also consistent with what we're seeing with other variants," she said.
"It's not surprising that that would be the case as well for omicron because the part of the immune system that is thought to mediate disease severity is less likely to be affected by all of these mutations."
Omicron spread
In the weeks since omicron was detected, South Africa has experienced rapid spread of the virus — concentrated in its most populous province, Gauteng.
The seven-day rolling average of daily new cases in the country rose over the past two weeks from 8.07 new cases per 100,000 people on Nov. 29 to 34.37 new cases per 100,000 people on Dec. 13, according to Johns Hopkins University. The death rate hasn't increased during that same period.
"The omicron-driven fourth wave has a significantly steeper trajectory of new infections relative to prior waves. National data shows an exponential increase in both new infections and test positivity rates during the first three weeks of this wave, indicating a highly transmissible variant with rapid community spread of infection," Noach said.
Although case numbers are rising, hospitalizations are not increasing at the same rate, leading the scientists to report that the risk of hospitalization from omicron is lower than delta or earlier variants.
Rasmussen said we shouldn't assume the risk of hospitalizations from omicron will be similar in Canada.
"In Ontario, for example, we're already seeing a very steep upward curve in the number of cases. Hospitalization and death are both lagging indicators of severity, meaning that it will be a couple more weeks before we have an idea if omicron is going to behave the same way in Canada," she said, adding that doing anything to reduce transmission including booster shots and mask mandates beyond provincial mandates are needed.
"Even if this does turn out to be mild, if it's more transmissible and you have more cases overall, even if it's a smaller percentage of those cases that develop severe disease, that still could potentially be a large number of people in terms of the absolute numbers."
Pfizer vaccine results
The South African analysis shows that people who received two doses of the Pfizer vaccine had 33 per cent protection against infection in the first weeks of South Africa's current omicron-driven wave.
That's a significant drop from the 80 per cent protection against infection afforded during earlier periods.
The researchers say it's encouraging that the study shows that people fully vaccinated with Pfizer have 70 per cent protection against hospital admission during the omicron surge. That's still a drop from the 93 per cent protection seen in South Africa's delta-driven wave.
The study shows that significant protection against hospital admission even among older age groups, with 67 per cent in people aged 60 to 69 and 60 per cent for people aged 70 to 79.
The South African analysis was based on examining more than 211,000 positive COVID-19 test results, 41 per cent of which were for adults who had received two doses of the Pfizer vaccine. About 78,000 of the positive results were attributed to omicron infections.
The South African analysis supports an earlier assessment by U.K. authorities.
The U.K. Health Security Agency said last Friday that new data from the U.K. confirms that omicron is more easily transmissible than other variants. Other studies suggest that both the AstraZeneca and Pfizer vaccines are less effective in preventing symptomatic infections in people exposed to omicron, though preliminary data show that effectiveness appears to rise to between 70 per cent and 75 per cent after a third booster dose.
The study also found that omicron poses a higher risk of reinfection. For individuals who have previously had COVID-19, the risk of reinfection with omicron is significantly higher than that of earlier variants.
Early results on Pfizer pill
More information came Tuesday from Pfizer, which announced that its experimental pill to treat COVID-19 — separate from its vaccine — appears effective against the new variant.
Pfizer also said full results of its 2,250-person study confirmed the pill's promising early results against the virus: The drug reduced combined hospitalizations and deaths by about 89 per cent among high-risk adults when taken shortly after initial virus symptoms.
Separate laboratory testing shows the drug retains its potency against the omicron variant.
Dr. Isaac Bogoch, an infectious disease specialist at University Health Network in Toronto, said the numbers are promising, but seeing how they work in real-time settings in Canada is needed.
But largely, he welcomes the news.
"Bring it on. We need it. We need therapeutics and we need them badly," he said.
"Most of our therapeutics are geared toward hospitalized individuals. This is a fantastic product because number one, it's a pill, not an infusion. And number two, it keeps people out of hospital."
With files from CBC's Stephanie Dubois
