(NEXSTAR) – The U.S. is seeing a late summer surge in COVID-19 cases, tracking from the Centers for Disease Control and Prevention shows.

The spike is particularly pronounced in one region of the country which includes Louisiana, along with Arkansas, New Mexico, Oklahoma and Texas, where about 15% of COVID tests reported to the CDC are turning up positive.

But practically the entire Western country isn’t far behind. A dozen more states west of the Mississippi reported test positivity rates about 10% last week.

In reality, the number of cases across the country is likely underreported as more people opt to test for the virus with at-home kits over lab tests.

Testing sewage and wastewater, albeit gross, can give us a better idea of how many people are sick with COVID in a certain area.

“Wastewater monitoring can detect viruses spreading from one person to another within a community earlier than clinical testing and before people who are sick go to their doctor or hospital. It can also detect infections without symptoms,” the CDC explains.

Wastewater data shows five states with “very high” virus activity levels: Alaska, Hawaii, Nevada, Texas and Utah.

Even wastewater data doesn’t give us the full picture, however, as some states have no testing sites or very few that report to the CDC.

The summer surge in COVID activity isn’t particularly surprising; the New York Times reports it’s a pattern that has occurred every summer since the beginning of the pandemic. Epidemiologists believe it’s because more people spend time in air-conditioned, poorly ventilated spaces that make it easy for the virus to spread. More people also travel over the summer, exposing themselves to large groups.

Immunity from the last COVID booster shot, often administered the previous fall, may also be fading by the time summer rolls around, Dr. Ziyad Al-Aly, a senior epidemiologist at Washington University in St. Louis, told the Times.

But fewer Americans could have access to a COVID-19 shot this year with changing regulations. The Food and Drug Administration this week approved updated Pfizer, Moderna and Novavax vaccines for seniors, but narrowed their access for younger adults and children without high-risk health conditions.

How hard it will be to get a shot (and to get the shot covered by health insurance) this fall and winter remains to be seen. A CDC panel is expected to meet in September.

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