The Covid-19 pandemic has been an immense challenge globally, with new variants of the SARS-CoV-2 virus continuing to emerge. The latest variant causing concern is known as XBB, a recombinant variant resulting from two different Omicron subvariants mixing. XBB has been detected in several countries already, leading to fears it could spread rapidly. So what is this new variant like and should we be worried?
The Origin and Spread of XBB
XBB is a recombinant of the BA.2.10.1 and BA.2.75 Omicron subvariants. It was first detected in India in August 2022 and has since been found in Bangladesh, Japan, Singapore, and over a dozen other countries.
Singapore has been closely monitoring XBB given its status as a travel hub. In early October 2022, XBB went from making up 22% of infected cases to being responsible for 54% of cases just two weeks later. This rapid growth rate suggests XBB may have a higher transmission rate than previous variants.
Key Mutations in XBB
XBB contains key mutations that are concerning for a few reasons:
- Increased ACE2 receptor binding affinity – A mutation in the receptor binding domain results in tighter binding to human ACE2 receptors, the doorway SARS-CoV-2 uses to enter and infect cells. This likely contributes to higher infectiousness.
- Higher antibody escape – Mutations in areas targeted by neutralizing antibodies generated after vaccination or prior infection enable greater immune evasion. This means vaccines and antibody treatments may be less effective.
- Higher spike stability – Changes in the spike protein likely make the spike more stable as an adaptation to increased population immunity, enhancing the virus's ability to infect cells.
Potential Risks of XBB
The combination of mutations relating to infectiousness, immune evasion, and spike protein stability have epidemiologists concerned about XBB for a few key reasons:
With its growth advantage over other variants, XBB can spread rapidly once introduced into a region. This increases the likelihood of bigger infection waves.
The immune evasive mutations make reinfections more likely, even in recently infected or vaccinated individuals. This could mean more repeat bouts of COVID-19.
Existing vaccines may provide less protection against infection and transmission with XBB. Boosters targeting Omicron help, but protection may still decrease over time.
It's unclear if XBB causes more severe illness compared to Omicron variants to date. Further real-world data is needed. Some experts think it may not be more virulent.
Challenges for Vulnerable Populations
Faster community spread and reduced vaccine protection raise risks for vulnerable groups if timely boosters are not administered before XBB is widespread locally.
XBB Monitoring and Precautions
Health authorities globally are closely tracking the spread of XBB through genomic surveillance networks. As more is learned about its infectiousness, ability to evade immunity, and disease severity, public health recommendations will be updated accordingly.
In the meantime, individuals can take reasonable precautions while going about normal activities:
- Get up-to-date on COVID-19 boosters, especially if you are elderly or immunocompromised
- Consider masking indoors or in crowded spaces if XBB is detected locally
- Get tested and isolate if you have symptoms to avoid spreading infection
- Improve indoor ventilation and air filtration where possible
- Practice good respiratory hygiene (masking when ill, cough etiquette, hand hygiene)
What the Future Holds
While the continual emergence of new variants is concerning, the population now has much stronger immunity through vaccines and prior infections compared to early in the pandemic. Our immune systems are better prepared to respond. Oral antiviral treatments are available to reduce the risk of severe illness in vulnerable groups.
Public health officials will calibrate recommendations to the characteristics of new variants like XBB. With reasonable precautions, societies can continue progressing towards a post-pandemic phase. But we must continue tracking viral evolution closely and use tools wisely to counter future surges. The pandemic marathon continues, yet the finish line is hopefully nearing.
Frequently Asked Questions about the new Corona variant
What is XBB and where did it come from?
XBB is a new recombinant variant of Omicron BA.2 that emerged in August 2022. It results from two different Omicron sublineages, BA.2.10.1 and BA.2.75, mixing during co-infection of a single host. It was first detected in India.
Is XBB more contagious than other variants?
Early data suggests XBB is among the most transmissible variants detected yet, spreading rapidly in multiple countries where detected. This is likely due to mutations enhancing ACE2 receptor binding affinity.
Are vaccines effective against XBB?
Unfortunately, immune escape mutations limit vaccine effectiveness against infection and transmission. However, boosters targeting Omicron sublineages provide better protection that wanes over time.
Does XBB cause more severe illness and death?
So far there is no clear evidence that XBB results in higher rates of severe outcomes. However data is still limited as it continues spreading globally.
What precautions should I take against XBB?
Get up-to-date on COVID-19 boosters, mask indoors if it is spreading locally, test and isolate if symptomatic, improve ventilation in shared spaces, and practice respiratory hygiene.