Negev Ben Gurion University in Israel released a statement on the 2nd that the research team led by the researchers of the University found that the delta virus was still "secretly spreading" while the transmission of the mutated novel coronavirus Omicron virus was accelerating. The researchers warned that when the Omicron strain "declines", the delta strain may "make a comeback". The researchers monitored the wastewater in the southern Israeli city of bersheba from December 2021 to January 2022. The results showed that the delta strain did not disappear at the time of the accelerated spread of the Omicron strain, but was still "secretly spreading". The prediction model developed by the research team shows that the transmission of Omicron strain will gradually weaken or even disappear in the next few months, but the delta strain will continue to spread, which may lead to a new wave of delta strain infection or the emergence of new threatening mutant strains. The researchers said that the epidemiological research based on wastewater is convenient and practical, which is helpful to epidemic prevention and control. The study was published in the academic journal holistic environmental science. So far, the World Health Organization has identified five variants of novel coronavirus that need attention, namely alpha, beta, gamma, Delta and Omicron. As the transmission power of the first three strains has been significantly weakened, who classified them as "previously transmitted strains requiring attention" and delta and Omicron strains as "spreading strains requiring attention". (Xinhua News Agency)