Israeli researchers warn of new international COVID wave, driven by Delta comeback

Omicron didn’t wipe out the previous variant, which is super-resilient and could reemerge with a vengeance, according to peer-reviewed study based on cutting-edge sewage monitoring

By Nathan Jeffay 4 May 2022, 3:24 pm Edit

Nathan Jeffay is The Times of Israel's health and science correspondent

There is a real danger of another international COVID wave this summer, with the Delta variant possibly poised to make a comeback, new Israeli research suggests.

The peer-reviewed study is based on cutting-edge Israeli monitoring of sewage, which reveals not only the prevalence of coronavirus cases, but also their variant.

It showed that even at the height of the Omicron wave, the previous Delta variant hadn’t been wiped out, even though it was expected to be based on the dynamics of previous waves.

After monitoring the patterns of the two variants, the researchers concluded that Omicron and its subvariants are likely to disappear soon, but Delta has shown such strong resilience that it could well reemerge.

“Our findings highlight that the pandemic is not over and suggest that sooner or later there will be another wave, potentially in the summer or at the end of the summer,” Prof. Ariel Kushmaro, who runs the Ben-Gurion University of the Negev wastewater lab that conducted the research, told The Times of Israel.

A father with the supervision of a Meuhedet Health care worker takes swab samples from a child at Meuhedet coronavirus testing center in Jerusalem, on January 18, 2022. (Olivier Fitoussi/Flash90)

He said that the significance extends far beyond Israel, and indicated that internationally, Delta still poses a larger threat than widely assumed. Delta could reemerge in its existing form, or could spread in the form of a new subvariant, he predicted.

Some COVID experts say that the study gives a clear basis in data for a warning they have been giving for weeks.

“The pandemic isn’t over, and this great piece of research provides clear findings that emphasize this and help us to understand the situation,” immunologist Dr. Yariv Wine, a Tel Aviv University academic who wasn’t involved in theBen-Gurion research, told The Times of Israel.

Kushmaro said that Delta’s resilience surprised his team. “In the past, we saw that when one variant rises, others disappear; but this just doesn’t seem to have happened with Delta, which seems to have a certain ability to survive,” he said.

Illustrative image: technicians take sewage samples in Israel as part of COVID-monitoring efforts. (MENAHEM KAHANA/AFP)

“In this study, we identified that even when Omicron was at its very highest in the wastewater, Delta was still circulating,” he added. “The patterns we see indicate that Omicron is in demise, but Delta has survived and is positioned to possibly reemerge.”

Kushmaro and his colleagues, including Dr. Karin Yaniv, wrote that according to their analysis model Delta is expected to continue to circulate largely undetected — what they call cryptic circulation — until it causes a wave. They published their findings in the journal Science of the Total Environment.

“According to the developed model, it can be expected that the Omicron levels will decrease until eliminated, while Delta variant will maintain its cryptic circulation,” they wrote. “If this comes to pass, the mentioned cryptic circulation may result in the reemergence of a Delta morbidity wave or in the possible generation of a new threatening variant.”