The newer and most contagious Omicron subvariants, known as BA.4 and BA.5, now make up over 70 percent of COVID-19 infections in the United States, according to data released by the U.S. Centers for Disease Control and Prevention (CDC) this week.

The BA.5 subvariant accounted for 53.6 percent of new infections in the week ending July 2, while BA.4 accounted for 16.5 percent of the new infections, CDC data showed.

BA.5 has become the dominant variant in the United States.

Health experts said the newer variants are more contagious and may pose a severe threat to immune protection.

They stressed that current public health tools are still very effective against BA.4 and BA.5, including masking indoors, avoiding crowds and getting booster shots.

The new subvariants are also driving a new wave of COVID-19 in Europe as Italy recorded more than 100,000 COVID-19 cases on Tuesday, marking the first time since February.

In response to the new wave, officials from the European Medicines Agency (EMA) stressed the importance of vaccination.

"As this new wave is unfolding across Europe, it is essential to maintain the protection of vulnerable groups and avoid any postponement of vaccination. The authorized vaccines still give good protection against increased hospitalization, severe illness and death," said Marco Cavaleri, head of biological health threats and vaccines strategy of the EMA.

(With input from Xinhua)