Australia, where the influenza season usually runs from June to September, saw two consecutive years of significant declines in influenza cases after the coronavirus epidemic hit in 2020. But cases have been increasing rapidly since the end of April this year.

According to the Australian Department of Health, some 88,000 cases of influenza have been reported this year through June 5. More than 50% of these cases, or slightly under 48,000, were diagnosed in the two weeks ending June 5.

Since mid-April, cases have continued to exceed the average of the past five years. The increase in patients began earlier than in previous years, such as 2019, before the pandemic, and the pace of increase has been much faster than in previous years.

Influenza and Covid-19, both respiratory illnesses, spread through similar routes of infection. They are also more prevalent in winter. Health experts have long warned about the possibility of twin epidemics, but the world has so far been spared that.

Measures taken against the coronavirus, such as wearing masks, washing hands and maintaining distance, as well as travel restrictions, were effective against influenza as well.

But as economic and social activities resume, the measures are being lifted. Fewer people are immune to influenza after two consecutive years of declined cases.

According to the World Health Organization, influenza cases are increasing in Australia, New Zealand, Chile and Uruguay.

In general, the situation in Australia is seen as a key indicator of what is to come in Japan.

“There is no doubt that Japan will also experience an influenza outbreak in the future as more people enter the country and contact opportunities increase,” warned Motoi Suzuki, director of the Center for Surveillance, Immunization and Epidemiologic Research at the National Institute of Infectious Diseases in Tokyo.

“The epidemic could begin earlier than in the past, in August or September, or could be larger in scale.”

In Japan, new coronavirus cases continue to decline at present, but infections could spread again toward winter.

Although more than 60% of the population has received three vaccine doses, its effectiveness in preventing infection and illnesses declines over time.

The Omicron variant continues to mutate to increase its ability to evade the immune system, and new mutant viruses may emerge.

“We need to put an influenza vaccination regime in place as soon as possible,” Suzuki said.