Since the delta variant became Utah’s dominant strain of coronavirus this summer, one age group has seen a sharp increase in the rate of hospitalizations per positive test: babies younger than one year old.
But epidemiologists say that’s likely because fewer babies are getting tested in summer months — not because the delta variant is actually more likely to cause serious illness.
“Last year, maybe people were testing whole day cares or testing as a screening technique, so a lot of babies that had mild COVID [tested positive],” said Dr. Leisha Nolen, an epidemiologist with the Utah Department of Health. “This year, if we’re only testing babies that have some symptoms, you’re missing out on those with mild infections.”
As of Thursday, the Utah Department of Health reported 1,596 cases among babies under age 1, with 84 of those hospitalized. But 19 of those hospitalizations have been reported since June 14, about two weeks after the delta variant became the dominant strain of the virus in Utah.
That’s about 9% of the 213 cases reported in that age group in the same timeframe — nearly double the hospitalization rate of 4.7% that the state was reporting as of June 14.
But that 4.7% included a time when widespread testing efforts meant more cases were being identified among all age groups, Nolen said — including babies, whose infections may have been identified through, say, tests of entire care centers.
“This is more related to what cases we’re seeing come through, rather than more significant illnesses in these kids,” Nolen said.
UDOH did not have test totals or the percentage of positive tests broken down by age over time, but the percentage of positive tests statewide has risen sharply since June 1, when the delta variant became dominant. That means a large number of asymptomatic or mild cases likely are going undetected.
With case numbers generally low among babies — no other age group has had fewer positive tests per capita — it’s also easier for a small increase in hospitalizations or a small decrease in positive tests to result in a big jump in hospitalizations per case.
The shift in hospitalizations per case in babies is “statistically significant,” said Dr. Andrew Pavia, a pediatric infectious diseases specialist at University of Utah Hospital. But the total number of hospitalizations of infants hasn’t risen noticeably in his practice the way they have for kids ages 1 to 5, he said.
One of those, a Salt Lake County child, was on a ventilator as of Thursday, according to county data.
Meanwhile, this week brought two of the highest single-day case totals for children ages 5 to 10, since the pandemic began. More than 160 kids tested positive Tuesday and again on Wednesday; case counts for this age group were higher on just ten previous days in the 17 months since the pandemic began.