Emergency doctors in the UK and US are seeing an increase in younger people being hospitalised with severe cases of COVID-19.
It comes as many states in the US are experiencing a surge in cases due to a combination of unvaccinated people and the more contagious Delta strain.
New data from Johns Hopkins University shows in 46 states the rates of new cases are at least 10 percent higher this past week than the previous. And in 31 states new cases are at least 50 percent higher than the previous week.
Director of the Centers for Disease Control and Prevention Dr Rochelle Walensky told CNN younger people are increasingly being hospitalised with COVID-19.
That's echoed by emergency physician Dr Howard Jarvis who says the patients he's seeing are younger than ever. He said unvaccinated people make up the vast majority of severe cases.
"If they're sick enough to be admitted to the hospital, they are unvaccinated. That is the absolute common denominator amongst those patients," he told CNN.
"Earlier in the pandemic, and certainly before we had vaccinations, we were seeing a much older patient population in the emergency department and getting admitted to the hospital.
"In recent weeks, we've been seeing a much younger population. We're seeing a lot of people in their 30s, 40s, early 50s. We're seeing some teenagers and some pediatric patients as well."
The wave of cases comes amid a new spike particularly in states with low vaccination rates such as Missouri.
So far 159 million people in the United States have been fully vaccinated - around 48.5 percent of the population. Unfortunately that is well below the estimated 70 to 80 percent needed to achieve herd immunity.
And it's not just US doctors who are seeing younger patients. In an article for The Guardian, an intensive care consultant in the north-west of England said COVID-19 wards are being overrun by sick patients, many of whom are under 60.
"The patients are younger this time. I've been looking after patients aged between 27 and 82 in critical care, but most are in their 30s, 40s and 50s. And the vast majority are either unvaccinated or have had one dose of the jab," the doctor wrote.
They also said healthcare workers are dealing with patients who are denying the virus exists even as "we strap oxygen masks to their faces".
"That is perplexing. Staff find that particularly hard and I think it will be an interesting and difficult part of this next phase. I wonder if we'll be caring for a select group of patients who think the very disorder we're treating them for is a sham. How do staff, who are so exhausted, navigate that?"
In the UK 34.8 million people are fully vaccinated or around 52.2 percent of the population. Wales has the highest vaccination rates at 58.2 percent followed by Scotland at 52.8 and England at 52 percent. Northern Ireland is falling slightly behind at 49.8 percent, according to Our World in Data.