A dangerous new Covid variant from China is surging in California, health officials warn. 

The California Department of Public Health issued a warning this week indicating that the highly transmissible NB.1.8.1 variant has now been identified in the state, marking it as the sixth state in the US to encounter this strain.

This variant has also been found in international travelers arriving in Washington state, Virginia, Hawaii, Rhode Island, and New York City since March.

Health officials said the variant was first detected in March and has been on the rise since May 1. 

Since April, NB.1.8.1 has increased from two percent of Covid cases in California to 19 percent, according to health department data. 

According to lab tests, NB.1.8.1, initially identified in China in January, appears to be more contagious than the strains currently in circulation, which could result in an increase in infection rates and hospitalizations.

World Health Organization data also suggests it makes up more than half the variants currently circulating. 

The warning comes as some physicians in California have called for the return of mask mandates to emulate countries like Hong Kong. 

Pictured above are people wearing face masks in China in 2023. The surge of Covid variant NB.1.8.1 has led some health experts in the US and abroad to suggest reinstating mask mandates 

Covid variant NB.1.8.1 has been detected in several US states, with California being one of the most recent

The California Department of Public Health told The Sacremento Bee: ‘COVID-19 continues to circulate in California and future seasonal increases in disease levels are likely.’

NB.1.8.1 is not yet prevalent enough in the US to be publicly tracked by the CDC. Strain LP.8.1 is currently the most dominant in the US, making up 73 percent of Covid infections. 

The latest vaccines target the JN.1 variant, which LP.8.1 is descended from. 

The California Public Health Department said: ‘Currently available vaccines are expected to remain effective.’

However, health secretary Robert F Kennedy Jr has moved to remove access to the Covid vaccine for healthy children and pregnant women. 

However, it is currently still on the CDC’s children’s vaccine schedule.

Covid tests in California as of April 19, the latest data available, show 2.1 percent of tests came back positive, a steady rate compared to weeks prior. 

The rate of hospitalizations from Covid during the week of April 19 in California was 1.3 per 100,000 people, a slight decrease from 1.6 per 100,000 the week before. 

There is usually a delay of several weeks for the most recent data, and infections can take several weeks to result in hospitalization. 

Nationally, Covid test positivity has decreased from 2.9 percent May 17 to 2.7 percent the week of May 24. Covid-related emergency department visits have also decreased 6.5 percent during that time frame.

Cases have been detected in the US, but they are few – with the positivity rate for the virus falling. This graph shows overall Covid cases by test positivity rate – or the proportion of swabs that detect the virus

In China, data shows the proportion of severely ill respiratory patients with Covid has jumped from 3.3 to 6.3 percent over the last month.

The proportion of Chinese ER patients testing positive for Covid had jumped from 7.5 to 16.2 percent.

Officials in Taiwan are also reporting a surge in Covid emergency room admissions, with the number rising 78 percent in a week over the seven-days to May 3, according to the latest data available.

And hospitalizations have risen to a 12-month high in Hong Kong, thought to be driven by the new variant. 

Symptoms of NB.1.8.1 are similar to other variants and include fever, chills, cough, shortness of breath, fatigue, muscle aches, headache, loss of taste or smell, sore throat, congestion, nausea, vomiting and diarrhea. 

Covid swabs cannot detect which variant you have.