A study that looked at how the immune system reacts to hot weather offers new insight into what's happening when the mercury rises.

Rio de Janeiro on Monday has declared a public health emergency because of an outbreak of mosquito-borne dengue fever, the city announced Monday, just days before Carnival celebrations kick off across Brazil.

The outbreak wasn't expected to derail Carnival, which officially starts Friday evening and runs until Feb. 14, but it has prompted a slew of special measures by the city in hopes of containing the illness.

According to Elon Musk, the first human received an implant from his computer-brain interface company Neuralink over the weekend.

In a Monday post on X, the platform formerly known as Twitter, Musk said that the patient received the implant the day prior and was "recovering well." He added that "initial results show promising neuron spike detection."

Winter is here, inflicting its usual array of symptoms — coughs, nasal congestion, fatigue and fever — and, this year, a new COVID-19 variant is dominating the scoreboard.

COVID-19 is leading hospital admissions among the respiratory viruses, according to the U.S. Centers for Disease Control and Prevention.

Face masks will be mandatory in hospitals and healthcare centers in Spain starting Wednesday due to a surge in respiratory illnesses, the Health Ministry said.

The new leftist minority coalition government is imposing the measure despite opposition from most of Spain's 17 autonomous regions.

France's National Assembly unanimously approved a bill to ban single-use, disposable electronic cigarettes, in an attempt to protect young people drawn to their flavors and mitigate the environmental impacts of the disposable products known as "puffs."

Lawmakers adopted the bill in a late-night vote on Monday by 104 in favor, zero against.

France will ban smoking on all beaches, in public parks, forests and some other public areas as part of a national anti-tobacco plan presented by the health minister on Tuesday.

Tobacco products cause 75,000 avoidable deaths a year in France, Minister of Health and Prevention Aurélien Rousseau said on BFM television. The government will introduce legislation at the start of next year to enlarge the scope of places where fines can be levied for smoking, he said.

A lack of clean water in the Gaza Strip is raising major concerns for human health.

"Gaza is running out of water, and Gaza is running out of life," said Philippe Lazzarini, chief of the U.N. agency for Palestinians.

Jill Biden is urging women to consult their doctors about getting mammograms or other cancer screenings, saying in a new public service announcement for Breast Cancer Awareness Month that early detection saves lives.

"October is Breast Cancer Awareness Month, and I'm asking you to put your health first," the first lady says in the 30-second spot recorded amid flower blooms in the White House Rose Garden.

Two scientists won the Nobel Prize in medicine on Monday for discoveries that enabled the development of mRNA vaccines against COVID-19 and could be used in the future to create other shots.

Katalin Karikó, a professor at Sagan's University in Hungary and an adjunct professor at the University of Pennsylvania, and Drew Weissman, of the University of Pennsylvania, were awarded the prize for "their groundbreaking findings, which have fundamentally changed our understanding of how mRNA interacts with our immune system," the panel that awarded the prize said.