Experts are warning that symptoms for those infected with the Delta variant of COVID-19 may not only be different than the original coronavirus strain, but they also may be more dangerous and transmissible.

The Centers for Disease Control and Prevention said this week that the Delta strain of the virus is a “variant of concern” that could lead to more deaths and hospitalizations, while the World Health Organization said Wednesday that the strain has been detected in more than 80 countries and continues to mutate as it spreads.

The Delta variant was initially identified in India and has now become the dominant variant in some countries like the U.K. It is also expected to become the main virus strain in the U.S., where it currently makes up 10% of all new cases, up from 6% a week ago, CNBC reported.

The New York Times reported that Chinese doctors say they are finding that symptoms of the Delta coronavirus are different and more dangerous than previous mutations. Now that the Delta variant is rapidly spreading, they are seeing patients become sicker and their conditions worsen more quickly.

Guan Xiangdong, director of critical care medicine at Sun Yat-sen University in the city of Guangzhou, China, told the Times that up to 12% of patients are becoming severely or critically ill within three to four days of the onset of symptoms, up from 2 to 3% in the past.

Brazilian and English doctors have reported similar trends with the variants in their countries, the news outlet said.

The WHO warned that the Delta variant could cause more severe symptoms but said additional research is still needed. But the organization maintained that there are signs that different symptoms are occurring in individuals who have contracted the Delta strain of the virus, CNBC said.

Symptoms commonly associated with the Delta variant include headaches, sore throat, runny nose, fever, with less pronounced incidents of cough and loss of smell reported less frequently, Tim Spector, a professor of genetic epidemiology at King’s College in London, told CNBC. He also said that younger people experience more of a bad cold or a “funny off feeling.”

A medical worker runs a rapid Covid-19 test at the Lope de Vega Cultural Center in the Vallecas neighbourhood, in Madrid A medical worker runs a rapid Covid-19 test at the Lope de Vega Cultural Center in the Vallecas neighbourhood, in Madrid Photo: AFP / OSCAR DEL POZO