Photo/Illutration A crowd at the Shibuya scramble crossing in Tokyo on July 18 (Kazuyoshi Sako)

The latest increase in novel coronavirus infections in Tokyo has already reached levels in the third wave but could worsen in the weeks ahead because of the more contagious Delta variant, heath experts warned.

According to the Tokyo metropolitan government’s data, the rolling seven-day average of new cases topped 1,000 on July 17 for the first time since Jan. 27 during the third wave.

As of July 18, the week-over-week rise in the seven-day average was 46 percent, a level higher than when Tokyo was placed under the second state of emergency on Jan. 7.

If the 46-percent pace continues, the seven-day average of new COVID-19 cases would hit 1,382 on July 23, when the Olympic Opening Ceremony is scheduled to be held, 1,478 on July 24, and 1,560 on July 25.

Tokyo’s highest seven-day average for new COVID-19 cases was 1,861, logged on Jan. 11.

The current surge of infections could soon overtake that record if the rate of increase surpasses 46 percent.

“We are in a very dangerous situation right now,” a metropolitan government official warned at a July 15 meeting on the infection situation in the capital. “You can be infected with the virus anywhere, and once infected, the virus will spread to family members and employees at workplaces.”

The seven-day average of new infections week on week began rising fast in July.

On July 13, the capital recorded a seven-day average of 791 new cases, up by 30 percent from the week earlier. Five days later, on July 18, the figure was 1,068, an increase of 46 percent.

When the second state of emergency was declared for Tokyo on Jan. 7, the week-on-week increase was 42 percent while the seven-day average was 1,261.

Hitoshi Oshitani, a professor of infectious diseases at Tohoku University who sits on the central government’s expert panel on the coronavirus, described the 42-percent rise as an “extremely unusual surge from an epidemiological viewpoint.”

On Dec. 31, 1,353 daily new infections were confirmed in Tokyo, 392 more than the previous record set a day earlier.

The number of new cases continued to soar in the following week,  pushing the health care system in the capital to the brink.

Tokyo set a record of 2,520 daily new cases on Jan. 7.

Oshitani said the sharp spike in winter can be traced back to a combination of exceptional circumstances in late December and early January.

One explanation, he said, is that more people got tested for the virus after year-end parties and other events. Other test-takers were alarmed by the COVID-19 death of Yuichiro Hata, a 53-year-old senior official of the main opposition Constitutional Democratic Party of Japan, in late December.

On Jan. 10, the seven-day average of new cases had shot up to 107 percent of the level of the previous week in Tokyo.

Different from the third wave of infections, the latest state of emergency was issued for Tokyo relatively early in the surge in cases. And more people have now been vaccinated against the virus.

But health experts are concerned that a week-on-week rise could further grow because of the Delta variant.

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