A new COVID-19 variant that appears to be the most contagious yet is spreading fast. The subvariant, called XBB, more than doubled COVID-19 cases in a day in Singapore last week and has just made an appearance in Hong Kong. Experts warn it could be on our doorstep this winter.

According to The Daily Beast, the new subvariant that is a mutated descendant of the omicron variant that swept America, is in many ways the worst form of the virus so far. Not only is it more contagious than its predecessors, it evades monoclonal therapy treatment, potentially rendering a whole category of drugs ineffective for COVID-19 treatment.

“It is likely the most immune-evasive and poses problems for current monoclonal antibody-based treatments and prevention strategy,” said Dr. Amesh Adalja, assistant professor at the Bloomberg School of Public Health at Johns Hopkins University Center for Health Security. But the good news is that the new bivalent boosters from Pfizer and Moderna seem to be effective against XBB, although the original vaccines are less effective, say experts. While vaccines won’t prevent all infections, they should prevent severe illness, Adalja said.

Dr. Peter Hotez, an infectious disease expert and vaccine specialist at Baylor College of Medicine, told The Daily Beast that as the novel coronavirus SARS-CoV-2 evolves and becomes more contagious and more resistant to certain types of drugs, your best precaution is to stay current with boosters as they become available.

Scientists say that the XBB has at least seven mutations along its spike protein. While this variant is fast becoming the dominant virus in many countries, there are several other “cousins” behind it, including BQ.1.1., which is spreading in Europe and is now in the U.S. And as the subvariants mutate, they become less recognizable to the existing antibody therapies. The current surge in Singapore may be the precursor to a global surge heading our way this winter or spring, says The Daily Beast.

Experts call the spread “unprecedented” and predict that the virus could morph into something out of the reach of science and its lagging vaccines.

“There have been times when different variants were on the move in different parts of the world, like the gamma variant in South America, and beta in South Africa,” Dr. Eric Topol, founder and director of Scripps Research Translational Institute told Fortune. “But this is different because now we have variants with extreme levels of immune evasion, and in any given country, potentially a few that could be in play at the same time.”

The best defense appears to be natural antibodies from a previous infection. People who were infected with the omicron variant this past year or late 2021 might still have good antibodies to fight the virus. Hotez says that the new bivalent boosters should work well against XBB and its descendants because they are closely related to the subvariant that the new formula was based on ─ BA.5.

But epidemiologists fear that one booster a year might not be enough to combat the virus as it continues to mutate at lightning speed and our antibodies wane in a few months. The big question is ─ can the vaccine industry sustain twice annual boosters, and will health agencies be able to approve them in a timely manner? And statistics show that people, especially Americans, have been slow to get their jabs. A mere 10% have gotten the bivalent booster that was approved by federal regulators last August.

According to Fortune, the virus may become more flu-like, hitting people harder in winter. In this case, a single, annual shot may suffice. But another scenario is that the virus will continue to spawn more superior variants, making it harder for those who develop vaccines and treatment even to keep up. Topol says that in this worst-case scenario, fully boosted but high-risk people, like the elderly, could be hit even harder than they are now. Like Hotez, and many other experts, his advice is to get a booster.

“We’ve got trouble ahead,” Topol said.