Kids make up largest share of recent COVID-19 cases, but will Omicron change that?

Children, ineligible for the vaccine until recently, have accounted for the largest portion of new COVID-19 cases since November, according to an analysis of Health Canada data. But with vaccine efficacy sharply lower against the extremely transmissible Omicron variant, medical experts are anticipating cases to rise across other age groups as well in the coming weeks.

The epidemic curve since early November to early December shows children under the age of 12 have consistently been the group with the most number of new infections, according to publicly available epidemiology data on COVID-19.

Data from the last two weeks out of Quebec, in particular, showed that children aged nine and under accounted for more than 5,400 COVID-19 cases, by far the largest of any age group.

“Now if the vaccines are not as effective against protecting against infection, but protecting against severe disease, I think that it will start to spread. These kids are going to infect their parents and the people who are around them younger or older,” said Dr. Earl Rubin, director of the Infectious Diseases division of the Montreal Children's Hospital.

“My projection is that whereas before, the overwhelming majority were school aged children, I think it is going to be a more equal distribution,” Rubin told CTVNews.ca in an interview on Friday.

In a weekly report for the week ended Dec. 4, those between the ages of five and 11 accounted for 23 per cent of the cases, at a rate of 153.3 cases per 100,000 people. Those between 30 and 39 accounted for 16 per cent of the new cases.

New daily cases across most age groups were decreasing by late November when global health officials began sounding the alarm on Omicron, whose arrival came just as Canadian officials gave the green light to begin vaccinating children aged five to 11.

“In the past few weeks, the highest incident rate of infection were really in unvaccinated children …The fact that right now [with Omicron] we have a whole bunch of kids and they’re not completely vaccinated, puts them at risk,” Dr. Anna Banerji, pediatric and infectious disease specialist with the University of Toronto’s Dalla Lana School of Public Health, told CTVNews.ca in an interview.

We need to be careful with children because they could have Omicron and transmit it, she cautioned. “Adults who are immunized or partially immunized, they’re at risk …we are going to start seeing a lot more cases of vaccinated people – which I think we're already starting to see,” she said.

Early data on Omicron suggests that vaccine protection against severe illness (as measured by hospitalizations) remains good at around 70 per cent, even though it is much lower than the 93 per cent against the Delta variant. It is the vaccine’s efficacy against infection that drops significantly, down to 33 per cent, compared to 80 per cent previously.

“I don't want people to get the idea that two doses of the vaccine are useless. I still think that they are very important for them to protect them against severe disease. I think it's really important that those who are eligible to get it, to get their third dose,” Rubin said.

“I don't want people to lose hope that the vaccines are not doing anything at this point. They certainly are.”

OMICRON AND WHAT LIES AHEAD

For now at least, hospitalization rates do not appear to be skyrocketing, but there is always a lag between infection and severe disease, and experts say there is still significant uncertainty over what to expect from Omicron.

Even if the vast majority of people who contract the Omicron variant are only mildly sick or even asymptomatic, experts say, the rate of transmission countries around the world are seeing means that hospitalization numbers could still balloon quickly.

“I hate to say it and don't want to be that Scrooge, ‘bah humbug’ – but the numbers, the epidemiology, are not in our favor,” Rubin said.

The expected pediatric hospitalization rate of those who are infected prior to Omicron, for example, was 0.3 per cent, according to Rubin. So even if fewer people got severely sick with Omicron, its staggering speed of transmission could still result in a higher number of people getting very sick.

“Hopefully it's not that more severe but if the numbers are higher, we will have to expect that the hospitalizations will go up as well. It does not necessarily reflect increased severity,” Rubin said.

Meanwhile, a study out of Imperial College London suggested that Omicron was showing no signs of being milder and that the variant’s risk of reinfection was more than five times higher than with Delta. This comes as the U.K. reported a record-breaking 93,045 new cases on Friday, with Omicron cases reportedly doubling roughly every two days. On Monday, daily new cases stood at just over 50,000.

The Ontario Science Advisory Table also noted this week that initial data from Denmark indicated that the percentage of Omicron cases requiring hospitalization was not any lower than other variants. In South Africa, the number of people dying during the current Omicron wave appear to be lower than in previous waves, but fewer deaths does not necessarily mean people are not getting severely sick. The advisory group noted a steep rise in hospitalizations following a surge in cases. The South Africa population is slightly different as well, said Rubin, noting that they were younger and may have already had COVID-19.

“The numbers going up are telling us that the vaccines aren't protecting against infection but hopefully protecting against severity,” said Rubin. 

Graphics by Deena Zaidi