(Bloomberg) -- An omicron subvariant appears to be even more contagious than the original fast-spreading strain, U.K. health authorities said, though vaccine booster shots remain an effective shield. 

Data from contact tracing showed the subvariant, BA.2, spread more frequently in households, the U.K. Health Security Agency said on Friday. Its rate of transmission among household contacts was 13.4%, compared to 10.3% for omicron. Though the data is a good indication of how transmissible the subvariant is, the agency cautioned that it’s preliminary and could fluctuate. 

Covid vaccines, in particular booster doses, were just as effective against BA.2, the agency said. By 25 weeks or more after the second dose, vaccines blocked 13% of cases -- a rate that rose to 70% two weeks after a booster.

“We now know that BA.2 has an increased growth rate which can be seen in all regions in England,” Susan Hopkins, the U.K. agency’s chief medical advisor, said in a statement. She urged residents to continue wearing masks, taking tests and getting vaccinated as the country lifts restrictions against the virus.  

In Germany, the new subvariant may delay the peak of the omicron wave slightly, Health Minister Karl Lauterbach said in a press briefing earlier Friday, before the U.K. data was released. However, authorities there still expect case numbers to begin receding by late February, he said.  

While there are some countries where the BA.2 is spreading strongly, such as Denmark, where it accounts for more than half of cases, it remains to be seen how worrisome the variant is, Bloomberg Intelligence analyst Sam Fazeli said on Bloomberg TV. 

The U.K. agency had identified 1,072 cases of BA.2 by Jan. 24, and said it has no data on the severity of the subvariant. Denmark, which has one of the highest vaccination rates, has said that so far it’s seen no difference in the rate of hospitalizations between the two. 

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