Should we be worried about the new strain XBB?

After two months of slowing down the epidemic, the number of new cases in Singapore in a single day exceeded 10,000 again on October 11 and is expected to peak in mid-November.

Where did the XBB strain that brought this "short but sharp" epidemic come from? Is it more dangerous? Do existing vaccines work?

Where are you from?

XBB, also known as BA.2.10 strain, is a new subtype mutant strain (subvariant) formed by the recombination of two Omicron strains.

The "X" in the

name stands for recombinant, and "BB" is the first letter combination of the two mutant strains it recombined - BA.2.75 and BJ.1.

XBB first appeared in India in August 2022, and has since been found in 17 countries including Australia, Bangladesh, Denmark, Japan, and the United States.

Why is it concerned?

XBB has attracted attention, firstly because it continues the characteristics of the omicron strain: strong infectivity.

has been present in local community cases since mid-September, and XBB has become the main strain currently circulating in the community in Singapore in less than a month.

According to Ministry of Health data, from October 3 to 9, patients infected with the XBB strain accounted for 54% of local community cases, more than those infected with BA.2.75 (24%) and BA.5 (21%).

In addition, the naming method of the XBB strain is different from the previous strain, which has also caused the XBB strain to gain more attention on social media. The spelling of XBB has led some netizens to regard it as the Chinese pinyin abbreviation of "little baby" and "little boy".

Is XBB more dangerous?

Although the XBB strain is more contagious, it does not mean a higher risk of severe illness. Local data show that the risk of hospitalization for new XBB cases in the past two weeks is about 30% lower than that of patients infected with the BA.5 strain.

Associate Professor Mai Xiwei, director of medical services at the Ministry of Health, said at a news conference on October 15: "Although the XBB strain is highly contagious, it is not necessarily more poisonous than other variants, and may cause more people to become seriously ill."


McSivey also said that according to the data available, no patients died from the XBB strain, entered the intensive care unit or required oxygen therapy.

Although the probability of severe illness is low, the Ministry of Health also pointed out that the public who have never been infected with coronary disease, or who have been infected for more than a year, are at the highest risk of contracting the XBB strain this time.

Can the vaccine work against XBB?

Dr. Siu Jieheng, an associate professor of the Department of Medical Technology and Informatics of the Hong Kong Polytechnic University, said in an interview with a local radio program that XBB is by far the most resistant to vaccine immune escape among many coronavirus variants. In other words, the antibodies produced by the vaccine are less effective at blocking the invasion of XBB.

Amesh Adalja, a public health expert at the Johns Hopkins Center for Health Security, also pointed out in an interview with The Daily Beast that the emergence of the XBB strain will pose challenges to current monoclonal antibody therapy (monoclonal antibody-based treatment).

So will the new bivalent vaccine work against the XBB strain? Adalia said the bivalent vaccine appears to be more effective against the XBB strain than the initial coronary vaccine. "Even in the face of immune-escaping strains, the vaccine is still useful against severe illness."


bivalent vaccine targets not only the original coronavirus, but also the Omicron variant. Because of this, the Ministry of Health of Singapore launched the Modena/Spikevax coronavirus bivalent vaccine for the public on October 14, three days earlier than originally planned.

At this stage, only persons over the age of 50 who have not met the basic vaccination requirements, or who have received supplements at least five months ago, can receive the bivalent vaccine.

Wearing a mask for protection in public places, and doing so as soon as possible when you can get the bivalent vaccine, seems to be the best way to fight the XBB strain at present.

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