COVID spikes will likely continue in 6-month seasonal and regional waves, experts say

As much of the country is beginning to experience the first glimpses of fall, states aren’t just ushering in cooler weather and pumpkin-spiced everything.

It’s the beginning of flu season, and for the past four years, the beginning of the winter COVID-19 wave.

But, unlike the flu, large case spikes are not restrained to the colder months, and two peak seasons have emerged for the virus.

Now, research from the University of Pittsburgh, University of Ottawa and University of Washington has shown that not only are there two seasonal COVID-19 waves, but the spikes in cases are also following a six-month pattern geographically.

The new study was published Sept. 16 in the peer-reviewed journal Scientific Reports.

“The COVID-19 winter waves are consistent with that of other respiratory viruses, but the existence of a repeated additional surge during the summer was unexpected,” Donald S. Burke, study author and dean emeritus of Pitt’s School of Public Health, said in a Sept. 16 news release from the University of Pittsburgh.

Here’s what you need to know.

Oscillating COVID waves

Using COVID-19 case and death data provided by The New York Times, researchers analyzed data from 937 days of the pandemic, ending in August 2022, according to the study.

When the data were put into what is called a “cross-date state rank correlation matrix,” cases from the 48 continental United States were compared to one another over time, creating what researchers called a “structured ‘checkerboard’ pattern.”

Thicker bands appeared where there were more cases, and the bands moved across the country as time passed, according to the study. The researchers then compared the national data to cases in individual counties and found the same trend.

On six month cycles, waves of higher COVID-19 cases appear to move north-south and east-west in addition to the seasonal trends that have been present since the beginning of the pandemic, according to the study.

“These waves start near the southern U.S. border in July and August, when the weather is hottest and the humidity is high — factors that usually tamp down the spread of respiratory viruses,” Burke said. “We don’t have a good explanation for why COVID-19 rates should increase in both the warmest and coolest times of the year.”

Health officials previously hypothesized that being stuck indoors with poor air circulation may be why more people get respiratory viruses in the winter. Then, research published in 2022 found that the immune response in the nose — where viruses often begin their invasion of the body — was subdued in colder weather.

In warmer temperatures, this isn’t the case, leaving researchers to wonder what biological mechanism makes COVID-19 stand out from similar viruses.

The amount of data analyzed in the study is “unprecedented,” researchers said, and should be used to navigate vaccination schedules.

“A full understanding of COVID-19 epidemic waves may be especially important given the fact that immunity to COVID-19 wanes. Rapid waning of human immunity to SARS-Cov-2 (the virus that causes COVID-19), both after infection or vaccination, has led to a public health strategy of frequent boosters,” researchers said. “For influenza, annual vaccinations are recommended to be given not earlier than October, to avoid too great a decline in immunity before the expected winter influenza surge. Similarly, SARS-Cov-2 vaccinations might ideally be timed to just precede the expected epidemic surge for any given U.S. region.”

Current COVID strains and recommendations

At the beginning of the summer, FLiRT subvariants, which originally stemmed from omicron, were dominating cases.

The variants, KP.2, is a descendant of JN.1, which rose to the top of the case-causing variants in late fall of last year.

FLiRT variants are still responsible for more than 60% of all cases, as of Sept. 18, according to the Centers for Disease Control and Prevention.

Now, a new omicron subvariant originally detected in Germany and spreading in Europe is worrying U.S. health officials going into winter, the Los Angeles Times reported.

The subvariant is called XEC, and it “is just getting started now around the world and here,” Eric Topol, director of the Scripps Research Translational Institute told the outlet in August. “And that’s going to take many weeks, a couple months, before it really takes hold and starts to cause a wave.”

Topol said the best way to be prepared is to be up-to-date on the CDC-recommended COVID-19 booster shots.

Positive COVID-19 tests increased in the second half of August, and pharmacies across the country have started to roll out the 2024 vaccines.

The boosters are recommended to everyone over the age of 6 months, the CDC says, but strongly recommended for those over the age of 65 or if you’ve never gotten a COVID-19 vaccine before.

It is safe to receive the COVID-19 booster and the flu shot at the same time, the CDC says. You can find vaccination locations near you here.