Registered nurse Julie Nelson, left,  vaccinates fellow registered nurse Monte Roberts for COVID-19 at LDS Hospital in Salt Lake City on Tuesday, Dec. 15, 2020.

Jeffrey D. Allred, KSL

Why are flu rates so low but COVID-19 continues to rise? Utah doctor explains

By Lauren Bennett, | Posted - Dec. 31, 2020 at 2:42 p.m.

SALT LAKE CITY — Flu rates in Utah and the United States continue to remain low, a trend first seen months ago in the southern hemisphere of the world.

While influenza infections are low, COVID-19 cases across the country are still rising with at least almost 1,000 reported every day in Utah since the end of September.

To some, the numbers don't make sense — if public health measures protect people from the flu and COVID-19, then why are novel coronavirus cases on the rise and flu cases so low?

The answer is really quite simple, according to Intermountain Healthcare infectious disease specialist Dr. Eddie Stenehjem.

"You had low flu coming into the U.S., you've got everybody wearing masks, you've got social distancing and you had the high rates of (flu) vaccination," Stenehjem said in a Q&A this week. "We really hope that kind of lets us ride out the flu season without seeing any significant activity of influenza."

As for why COVID-19 cases haven't gone down? Here's what Stenehjem said.

The novel coronavirus is more contagious than the flu.

Scientists use a mathematic term called R0 (pronounced R-naught) to indicate how easily a disease or virus spreads from person to person in a community.

Experts have calculated COVID-19's average R0 to be around between 2 and 4, meaning an infected person can spread the disease to two or more people, the World Health Organization said in a June report. For comparison, the average R0 for influenza in the 1918 Spanish flu pandemic was roughly between 1 and 2, according to an article published in BMC Medicine.

The number can vary widely even between different areas and states and depending on the outbreak.

The R0 is fluid and doesn't paint a full picture of how contagious a disease is but it does provide a starting point, despite its many limitations. One thing, however, remains clear: COVID-19 is more contagious than the flu.

It was already in the community

COVID-19 has been spreading in communities since the spring, meaning when winter came around, the virus was already widespread, Stenehjem explained.

The flu, on the other hand, usually is brought into a community from the southern hemisphere. But, with low cases of flu there, it never really made it over here, he said.

This time last year, Intermountain saw about 80-100 flu cases daily. This year, the health care system has only reported a handful of cases over the last few months.

Intermountain hospitals are actively looking for flu cases with extensive testing, Stenehjem said.

"It's not from lack of looking, it's just that we're not seeing influenza," he said.

The Utah Department of Health tracks flu cases in the state as well and as of the week of Dec. 13-19, cases remained low. So far this flu season, which began in early October, a total of seven people have been hospitalized with the flu.

"We're really not seeing a lot of other viruses circulating in Utah," Stenehjem said. "COVID-19 is by far and away the most prominent respiratory viral infection that we're seeing here in Utah."

We don't have a COVID-vaccinated population

In recent weeks, COVID-19 vaccines have been rolling out across the state to those eligible to receive it in the first phase — but the population is nowhere near herd immunity.

Flu vaccinations, on the other hand, have largely been up across the country.

The U.S. Centers for Disease Control and Prevention reported 192.3 million flu shot doses have been distributed as of last week and it's possible up to 198 million doses could be distributed in the 2020-21 season. Those numbers are up significantly from 2019, where 174 million were distributed across the 2019-2020 flu season.

For Utah, several age groups appeared to have a higher number of flu vaccinations reported this year when compared to last year, according to the Utah Department of Health.

However, it's important to note some age groups did not follow the pattern and reported lower flu vaccination numbers than in 2019, such as the 6-month to 4-year-old age group.

Overall, flu vaccinations nationwide appear to be up from last year, which Stenehjem said contributes to the low flu numbers.

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