Hello Health Rounds readers! Today we report on a troubling health trend among youth in many countries, and a study that found the latest flu shot is not optimally matched with the current dominant strain of the virus but will still likely keep you out of the hospital. We also highlight early research of a new, potentially safer delivery method for a hormone used to treat osteoporosis.  

See these breaking news stories from our Reuters team: Trump plans more steps to cut healthcare costs; global drugmakers rush to boost US presence as tariff threat looms; US and European aid cuts could result in 22.6 million deaths worldwide; WHO to lose a quarter of its workforce by mid-2026 and Ethiopia says three dead in Marburg virus outbreak.

With more than a half-million people worldwide dying from heat-related causes every year, a group of philanthropies is putting $300 million into developing life-saving solutions as global temperatures continue to rise. Read more here.

The worldwide prevalence of high blood pressure in children and adolescents nearly doubled between 2000 and 2020, new research shows, with obesity potentially driving the increase.

In 2000, about 3.2% of children had hypertension. By 2020, the prevalence had increased to more than 6.2% of children and adolescents under age 19, affecting 114 million young people around the world, according to a report in The Lancet Child & Adolescent Health.

The study also found that an additional 8.2% of children and adolescents have blood pressure levels higher than normal but do not yet meet the criteria for hypertension.

Obesity may be a substantial driver of the increase in childhood hypertension, the data suggest.

Nearly 19% of children and adolescents living with obesity were hypertensive, compared to less than 3% of children and adolescents considered to be at a healthy weight.

Obesity can cause other health problems, such as insulin resistance and changes in blood vessels, which make it harder to keep blood pressure within a healthy range, the authors noted.

Reviewing data from 96 studies involving more than 443,000 children in 21 countries, the researchers found that how blood pressure is measured in children and adolescents can affect prevalence estimates.

When hypertension is confirmed by a healthcare provider over at least three in-office visits, the prevalence was estimated to be about 4.3%.

However, when out-of-office assessments such as home blood pressure monitoring were included, the prevalence of sustained hypertension climbed to about 6.7%.

The research highlighted that conditions like masked hypertension, in which the condition is not detected during routine checkups, affect nearly 9.2% of children and adolescents globally, indicating potential underdiagnosis.

Conversely, the prevalence of white-coat hypertension – that is, when blood pressure is elevated only in the presence of a healthcare provider but is normal at home - was estimated at 5.2%, which suggests that a notable proportion of children might be misclassified, the researchers said.

The 2025–2026 flu vaccine is not an ideal match for the unexpected strain of the influenza A/H3N2 virus, called subclade K, that has been driving up infection rates in Canada, England, and Japan and will likely cause increased cases in the United States as well, researchers say.

But the 2025–2026 vaccine should still offer powerful protection against severe illness, they also emphasize.

“After a period of minimal change following the COVID-19 pandemic, influenza A/H3N2 viruses started to evolve in important ways during the northern hemisphere's 2024–2025 influenza season,” Canadian researchers reported in the Journal of the Association of Medical Microbiology and Infectious Disease Canada.

The virus evolved further during the southern hemisphere’s 2025 winter flu season. The A/H3N2 subclade K variant that arose “is projected to predominate during the northern hemisphere's 2025–2026 influenza season,” the Canadian authors said.

England may be looking at one of the toughest winters in its history "as an early wave of flu sweeps the nation,” according to a separate report published in The BMJ.

Antonia Ho, an infectious diseases researcher at the University of Glasgow, said in The BMJ report that of the two seasonal influenza A viruses, the current dominant circulating A/H3N2 virus tends to cause more severe illness than A/H1N1, particularly in older adults.

A November 11 report from the UK government that has not yet undergone peer review suggests that the 2025-26 vaccine is currently 70%-75% effective at preventing hospital visits in children aged 2-17 years and 30%-40% effective in adults, despite the dominance of the A/H3N2 strain.

So far, “this is broadly in line with a typical flu season,” the BMJ authors noted.

A new method of delivering a key hormone treatment for osteoporosis could help strengthen weakened, brittle bones without the usual uterine side effects that increase cancer risks, experiments in mice suggest.

Estradiol - a form of the estrogen hormone - is usually broken down in the body before it can reach the bones, with a resulting increased risk of endometrial and uterine cancers.

To bypass the uterus and other organs and deliver estradiol directly to the bones, researchers encapsulated it in a two-layer cage, or shell, that stays intact in neutral pH solutions, like in the bloodstream, but dissolves and releases the drug in acidic solutions, akin to the environment in weakening bones, according to a report in ACS Nano Letters.

In mice with postmenopausal osteoporosis, the researchers administered twice-weekly injections of their caged estradiol, regular estradiol, or saline. After four weeks, mice that received the caged estradiol achieved bone density values higher than pre-osteoporosis levels without uterine side effects.

Fluorescence imaging of the mice confirmed that the hormone concentrated only in the weakened bones.

The researchers hope their new drug-delivery system will eventually lead to more effective treatment of postmenopausal osteoporosis in humans.

“Our next focus will be developing an oral double-coated estradiol pill,” study leader Xi Chen of the East China University of Science and Technology in Shanghai said in a statement.