People urged to stay vigilant as coronavirus infections rebound in Japan — again

Merely two months after the peak of the sixth wave, coronavirus infections are already rebounding in Japan, with experts again urging people to stay vigilant by getting vaccine booster shots, wearing masks and avoiding crowded places.

The seven-day average of new COVID-19 infections stood at 46,594 as of Tuesday, up from 43,250 the week before and increasing for two weeks in a row. New infections had been gradually declining for several weeks after the government in January began implementing quasi-emergency measures, which restricted business hours for restaurants and some activities.

The lifting of those measures nationwide in late March, an uptick in people’s movement around the April start of the new school and business year, and the spread of the highly transmissible BA.2 omicron subvariant are seen as factors behind the rebound. Experts said the situation needs close monitoring given that new cases are increasing in all age groups, but particularly among teens and those in their 20s.

Low vaccination rates among young people were discussed in a meeting Thursday between Prime Minister Fumio Kishida and Shigeru Omi, the nation’s top coronavirus adviser. In an apparent attempt to entice younger people to get their third jabs, the government is reportedly considering offering discounts for music and sports events to people who have received booster shots.

“The level of new infections remains higher than in the peak we experienced last summer, and a potential rebound is a concern,” Takaji Wakita, chair of the health ministry’s COVID-19 advisory board, said after its weekly meeting Wednesday.

On the bright side, as the weather gets warmer, it becomes easier for people and businesses to ventilate indoor spaces, which can help reduce infections, Wakita said. People will also spend less time indoors, helping prevent the spread of the virus, he said.

But Hiroshi Nishiura, a mathematical modeling expert at Kyoto University, presented a grimmer outlook, saying “a seventh wave has already started.” He cited a resurgence in infections in many prefectures in recent days.

The pathogen fueling the current case increase is the BA.2 sublineage, a heavily mutated version of the coronavirus. BA.2 is more transmissible than the original omicron variant, BA.1, which led to record numbers of infections in Japan in February. Now accounting for 70% of new cases, BA.2 is expected to make up 90% of all new cases by the first week of May, according to surveillance data provided by the National Institute of Infectious Diseases.

Between the two variants, there has been no difference reported when it comes to vaccine efficacy or the risk patients will develop severe symptoms, meaning the treatments and prevention measures needed will be the same, said Motoi Suzuki of the NIID.

As the coronavirus continues to mutate, a new set of highly transmissible variants known as “recombinant variants” have been detected overseas. A recombinant variant occurs when an individual becomes infected with two or more variants at the same time, resulting in a mixing of their genetic material within the patient’s body, according to the U.K. Health Security Agency. The U.K. has already reported more than 600 cases of XE — a recombinant of the omicron variant’s BA.1 and BA.2.

In China, which is seeing its biggest outbreak since the coronavirus was first detected in Wuhan, authorities have reported two novel omicron subvariants that don’t match any existing sequences, according to Bloomberg News. It’s unclear how serious the symptoms caused by them are and whether they pose a significant risk.

Nishiura said Japan should also keep an eye on XE and other new variants.

“XE’s transmissibility is certainly higher than that for BA.1 or BA.2,” Nishiura said. “If people’s international mobility increases, XE has a high chance of replacing the current omicron variants. But we still don’t know the severity of symptoms among the infected people, so we need to examine the epidemiological impact of the variant closely.”

The omicron variant, first detected in South Africa last November, quickly overtook delta as the dominant strain worldwide. Many people infected with the omicron variant have developed mild or no symptoms, although the variant is far more infectious than delta. More recently, BA.2 has fueled a resurgence of infections worldwide.

BA.2’s generation time, or the time between the start of infection in a primary case and the start of infection in a secondary case, is slightly shorter than with BA.1, with both at around two days. Omicron’s generation time as a whole is also shorter than delta’s, which is around five days. The shorter the generation time, the harder it becomes to control an outbreak.