New study from Japan shows SARS-CoV-2 Omicron XBB.1.5 variant is highly transmissible and infectious
Team led by Japanese researchers characterizes the SARS-CoV-2 Omicron XBB.1.5 variant and assesses its danger to global public health
Peer-Reviewed PublicationIMAGE: THE SARS-COV-2 OMICRON XBB.1.5 VARIANT SPREADS RAPIDLY AND IS MORE INFECTIOUS THAN ITS HISTORIC PRECURSOR view more
CREDIT: KEI SATO FROM THE UNIVERSITY OF TOKYO, JAPAN
COVID-19 has caused significant global panic after its rapid emergence more than 3 years ago. Although we now have highly effective vaccines against the SARS-CoV-2 virus, which causes COVID-19, scientists continue to study emerging SARS-CoV-2 variants in order to safeguard public health and devise global preventive strategies against emerging variants. A team led by Japanese researchers has recently discovered that the SARS-CoV-2 Omicron XBB.1.5 variant, prevalent in the Western hemisphere, has high transmissibility and infectivity.
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been responsible for millions of deaths worldwide. Although scientists have designed novel vaccines to counter COVID-19, they are constantly on the lookout for emerging variants that can bypass vaccine resistance and potentially jeopardize global public health. A team led by Japanese researchers has recently been successful in characterizing the new SARS-CoV-2 Omicron XBB.1.5 variant, which was first detected in October 2022. Their findings were published on January 31, 2023 in volume 23 of The Lancet Infectious Diseases.
Says senior author Prof. Kei Sato from the Division of Systems Virology, The Institute of Medical Science, The University of Tokyo, Japan, “Because the Omicron XBB.1.5 variant can spread more rapidly than previous variants and has a potential to cause the next epidemic surge, we should carefully monitor it to safeguard public health.”
While studying emerging variants of the SARs-CoV-2 Omicron lineage, the research team made a startling discovery: the SARS-CoV-2 Omicron XBB.1.5 variant has a novel mutation in the spike (S) protein—the protein that anchors the virus firmly to the human angiotensin converting enzyme-2 (ACE2) receptor, thus facilitating the invasion of human cells. The serine-to-proline amino acid mutation noted at residue no. 486 in the S protein is virologically concerning because of a variety of reasons.
Sharing his concerns, first author Keiya Uriu from the Division of Systems Virology, Department of Microbiology and Immunology, The University of Tokyo, Japan, says, “In late 2022, the SARS-CoV-2 Omicron BQ.1 and XBB lineages, characterized by amino acid substitutions in the S protein and increased viral fitness, had become predominant in the Western and Eastern Hemisphere, respectively. In 2022, we elucidated the characteristics of a variety of newly emerging SARS-CoV-2 Omicron subvariants. At the end of 2022, the XBB.1.5 variant, a descendant of XBB.1 that acquired the S:S486P substitution, emerged and was rapidly spreading in the USA.”
To gain mechanistic insights into the infectivity, transmissibility, and immune response associated with XBB.1.5, the team conducted a series of experiments. For instance, upon conducting epidemic dynamics analysis—statistical modeling that facilitates the analysis of the general characteristics of any epidemic—the team realized that the relative effective reproduction number (Re) of XBB.1.5 was 1.2-fold greater than that of the parental XBB.1. This indicated that an individual with the XBB.1.5 variant could infect 1.2 times more people in the population than someone with the parental XBB.1 variant. Moreover, the team also realized that, as of December 2022, XBB.1.5 was rapidly outcompeting BQ.1.1, the predominant lineage in the United States.
Co-first-author Jumpei Ito from the Division of Systems Virology, remarks, “Our data suggest that XBB.1.5 will rapidly spread worldwide in the near future.”
The team also studied the virological features of XBB.1.5 to determine how tightly the S protein of the new variant interacts with the human ACE2 receptor. To this end, the researchers conducted a yeast surface display assay. The results showed that the dissociation constant (KD) corresponding to the physical interaction between the XBB.1.5 S receptor-binding domain (RBD) and the human ACE2 receptor is significantly (4.3-fold) lower than that for XBB.1 S RBD. “In other words, the XBB.1.5 variant binds to human ACE2 receptor with very high affinity,” explains Shigeru Fujita from the Division of Systems Virology.
Further experiments using lentivirus-based pseudoviruses also showed that XBB.1.5 had approximately 3-fold higher infectivity than XBB.1. These results suggest that XBB.1.5 exhibits a remarkably strong affinity to the human ACE2 receptor, which can be attributed to the S486P substitution.
The study by Prof. Sato and his team led to another important discovery from an immunization perspective. The XBB.1.5 S protein was found to be highly resistant to neutralization antibodies elicited by breakthrough infection with the BA.2/BA.5 subvariants. In other words, patients with prior infection from the BA.2/BA.5 subvariants may not show robust immunity against XBB.1.5, increasing their chances of infection and disease.
“The results of our virological experiments explain why the Omicron XBB.1.5 variant has a higher transmissibility than past variants: This variant acquired strong binding ability to human ACE2 while maintaining a higher ability to escape from neutralizing antibodies,” says Yusuke Kosugi from the Division of Systems Virology, Department of Microbiology and Immunology.
Contributing members of The Genotype to Phenotype Japan (G2P-Japan) Consortium conclude, “The SARS-CoV-2 Omicron XBB.1.5 variant does show enhanced transmissibility. Although few cases have been detected in the Eastern hemisphere, it could become a looming threat. Imminent prevention measures are needed.”
Thanks to the research team for the early warning! Meanwhile, we must continue adopting safe practices to defend ourselves from XBB.1.5.
JOURNAL
The Lancet Infectious Diseases
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Enhanced transmissibility, infectivity and immune resistance of the SARS-CoV-2 Omicron XBB.1.5 variant
Tune in, wash hands: COVID-19 TV coverage added momentum to hand hygiene boom
Researchers from Osaka University fortuitously find COVID-19 skyrocketed hand hygiene compliance, and the amount of network TV coverage of the pandemic was connected with that rise
Peer-Reviewed PublicationIMAGE: COMPLIANCE OF HAND HYGIENE AMONG VISITORS AT THE ENTRANCE HALL OF THE HOSPITAL. view more
CREDIT: 2023, ASAKO MIURA, THE IMPACT OF TELEVISION ON-AIR TIME ON HAND HYGIENE COMPLIANCE BEHAVIORS DURING COVID-19 OUTBREAK, AMERICAN JOURNAL OF INFECTION CONTROL
Osaka, Japan – Long before COVID-19, washing and sterilizing hands were known to help prevent the spread of infections such as influenza, and hand hygiene practices were especially important in high-risk areas, such as hospitals. So it was something of a public health boon that COVID-19 abruptly increased hand hygiene awareness. A new study also found that media coverage of the pandemic had a knock-on effect.
The study, from Japan’s Osaka University, gained unique insight on how COVID-19’s onset and media coverage of the novel virus raised hand hygiene compliance from 5% to over 70% in a matter of months. The study’s researchers tracked whether TV coverage related to such compliance and sought correlations between hand hygiene and newly confirmed COVID-19 cases and deaths. They published their findings in the American Journal of Infection Control.
“We were routinely monitoring hospital visitors’ use of hand sterilizer in December 2019 because of the influenza season,” explains lead author Daiichi Morii. “The timing just happened to correspond with the pandemic onset. That let us compare hand hygiene compliance before, during, and after the onset.” As another research variable, TV coverage was used as a symbol of the degree of social concern about COVID-19, and looked at its correlation with compliance.
Visitors were observed to see whether they voluntarily used alcohol spray on their hands upon entering hospital premises. During the baseline observation period in December 2019, just 5.3% of the observed visitors sanitized their hands. On January 28, 2020, the number rose modestly to 7.6%. Then, as COVID-19 quickly emerged, things took a dramatic shift – compliance rose to near 70% by August 2020 and remained at 70%–75% until October 2021, before very gradually declining.
At the same time, the researchers wanted to examine how the level of societal concern affected hand hygiene compliance. “Media coverage can have a strong psychological impact and affect public concern,” notes co-author Asako Miura. “So we looked at on-air time covering COVID-19 on Japan’s national public TV broadcaster, NHK, in the region where the hospital is located. The time spiked at 7.7 hours/day in May 2020, and then varied depending on the infection trend.”
The researchers ran mathematical simulations to pair TV coverage with compliance, and found a strong statistical correlation – an added hour of news coverage increased compliance the next day by around 1%. They also tracked the trends in newly confirmed COVID-19 cases and deaths, but found no correlation with hand hygiene compliance.
Despite the huge increase in hand hygiene compliance when there’s an epidemic onset, and the evident role media plays in that compliance, complacency can set in. People hear the same warnings over and over, as the authors note, and grow tired of them. More research is therefore needed into how to maintain the positive impacts seen in this study. That maintenance could lead to a future with less infectious disease, and clean hands.
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The article, “The impact of television on-air time on hand hygiene compliance behaviors during COVID-19 outbreak,” was published in the American Journal of Infection Control at https://doi.org/10.1016/j.ajic.2023.03.001.
About Osaka University
Osaka University was founded in 1931 as one of the seven imperial universities of Japan and is now one of Japan's leading comprehensive universities with a broad disciplinary spectrum. This strength is coupled with a singular drive for innovation that extends throughout the scientific process, from fundamental research to the creation of applied technology with positive economic impacts. Its commitment to innovation has been recognized in Japan and around the world, being named Japan's most innovative university in 2015 (Reuters 2015 Top 100) and one of the most innovative institutions in the world in 2017 (Innovative Universities and the Nature Index Innovation 2017). Now, Osaka University is leveraging its role as a Designated National University Corporation selected by the Ministry of Education, Culture, Sports, Science and Technology to contribute to innovation for human welfare, sustainable development of society, and social transformation.
Website: https://resou.osaka-u.ac.jp/en
Number of newly confirmed cases in the Osaka Prefecture.
The on-air time of COVID-19 related news.
CREDIT
2023, Asako Miura, The impact of television on-air time on hand hygiene compliance behaviors during COVID-19 outbreak, American Journal of Infection Control
JOURNAL
American Journal of Infection Control
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
People
ARTICLE TITLE
The impact of television on-air time on hand hygiene compliance behaviors during COVID-19 outbreak
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