New surge in COVID-19 cases across Japan prompts alarm

Once again, COVID-19 cases are surging across Japan, fueled in part by the newer, immunity-escaping omicron subvariant BA.5, raising concerns that the nation’s seventh wave has begun.

Nationwide, daily new infections topped 45,000 on Wednesday — nearly double the figure from last week and on par with the level seen in mid-May. The surge comes as people are planning summer holidays and large, in-person events have begun to return. At the same time, the number of ambulance calls due to heatstroke is growing.

The government has ruled out the possibility of imposing quasi-emergency measures any time soon, but it is considering whether to expand its vaccination program so that fourth shots — currently administered only to those at-risk and residents age 60 or older — can be offered to more people. Some experts, meanwhile, have also urged the government to swiftly make the fourth dose available to medical and nursing care workers in order to prevent cluster infections on the front line.

“We are weighing the fourth shot as we continue to collect scientific insight (on the effectiveness of the second booster shot),” Deputy Chief Cabinet Secretary Seiji Kihara told a news conference on Thursday.

In Tokyo, where 8,529 new cases were reported Thursday, experts expressed concern about both the spike in cases and hospitalizations. As of Thursday, 1,448 people were hospitalized in the capital, up from 907 a week before and more than double the level two weeks before.

“We fear this could severely impact our health care system,” Norio Ohmagari, a top medical adviser to the Tokyo Metropolitan Government, told a panel monitoring the capital’s COVID-19 response. “We need to urgently strengthen our health care system (for COVID-related care) while eyeing its balance with the normal health care system.”

The omicron subvariant BA.5, first detected in South Africa in February and recently fueling infections worldwide, is rapidly replacing BA.2, another subvariant of the omicron family that remains dominant in Japan.

Tetsuo Nakayama, a project professor at Kitasato Institute for Life Sciences, said the recent jump in Japan’s infections is attributable in large part to low vaccination rates among people between 20 and 49 years old.

Government data shows that while more than 80% of people in Japan have received two coronavirus vaccine shots, only 62.1% had completed a third jab as of Thursday. In addition, as of Monday, third-jab rates hovered at 45.9% for people in their 20s, 49.6% for those in their the 30s and 58.7% for people in their 40s. In contrast, over 90% of people in their 70s and older have received three shots, while the rollout of a fourth round started in late May and is currently in progress.

“Many young people received their second shot around last fall,” Nakayama said by phone. “Which means more than half a year has passed and their immunity has significantly waned. Also, the current vaccine is based on the original Wuhan strain, which is quite different (from the heavily mutated omicron subvariants).”

The highly transmissible BA.4 and BA.5 sublineages feature mutations in their spike protein, through which they have acquired an ability to escape immunity gained through vaccinations or infections, experts say. So far, there is no proof of these subvariants causing more severe symptoms, according to the National Institute of Infectious Diseases (NIID).

Despite this, Nakayama stressed the benefits of booster shots, saying the current vaccine is still effective in preventing severe cases and hospitalizations.

Some experts are calling on the government to quickly expand the nation’s coverage of fourth vaccine shots to front-line medical and nursing care workers. For the fourth dose, Pfizer and Moderna vaccines have been approved.

Hiroshi Nishiura, an epidemiologist at Kyoto University, is one of the experts advocating for expanding the additional vaccine shot to health care workers. “Cluster infections at medical institutions accepting (COVID-19 patients) have begun to be observed,” he said in a tweet on Thursday. “Boosters for medical and nursing care workers... feel necessary.”

Nakayama agreed, noting that ambulance workers — who are at the forefront of COVID-19 emergency response — are also at high risk and should be covered.

According to the NIID, which conducts genomic surveillance of virus samples collected from across Japan, the ratio of BA.5 variants detected began rising from nearly zero in the last week of May. It’s currently estimated to comprise 24% and rise even further to nearly half of all strains later this month.

BA.4, also first detected in South Africa in January, is the other omicron subvariant raging in other countries including the U.K. and the U.S. So far, it hasn’t grown as quickly in Japan, though the subvariant has already been detected both at airport screenings and in communities.

In Tokyo, BA.5 cases jumped to 33.4% of the total during the week of June 21-27, up from none five weeks before, while BA.4 cases accounted for 4.2% of the total, up from zero two weeks before. BA.2.12.1 cases accounted for 4.5%, while the remaining 57.8% cases were BA.2.

New infections driven by the original omicron variant soared across Japan during the sixth wave, which started in January, eventually surpassing 100,000 in February. The cases subsequently went down as the population’s immunity increased through booster shots and infections. Cases began to increase again in the second half of June, posting week-on-week growth for 16 straight days through Wednesday.