Nearly half a million people in Tokyo are likely to have been infected with COVID-19 by last March — nearly quadruple the number of official cases announced by the Metropolitan Government — according to a recent study.
The estimate was made by a team of researchers led by the Tokyo Metropolitan Institute of Medical Science that examined 23,234 randomly selected serum samples from patients at 14 Tokyo hospitals taken between Sept. 1, 2020, and March 31 this year, checking for SARS-CoV-2 antibodies.
Although none of the patients whose samples were examined had been diagnosed with COVID-19 or exhibited any symptoms at the time of their blood collection, the researchers found that the overall seroprevalence, or percentage of individuals in a population who have developed antibodies against the disease, was 1.83%, while the rate last March — the most recent month in which samples were tested — was 2.7%.
After adjusting for population age, sex, and region, the researchers estimated that the seroprevalence in Tokyo, which had a population of around 14 million last year, was 3.40% — indicating that 470,778 individuals had been infected with COVID-19 by March, they said.
“The estimated number of individuals in Tokyo with a history of SARS-CoV-2 infection was 3.9-fold higher than the number of confirmed cases during the period,” according to the study, which has undergone a full peer review and was released Saturday in the Japan Epidemiological Association’s advance online publication of the Journal of Epidemiology.
The research shows the novel coronavirus to be an inscrutable disease. While 10% to 20% of symptomatic patients infected with COVID-19 experience severe symptoms and are at considerable risk of death, many are asymptomatic or see only mild symptoms, making it difficult for the authorities to accurately track the spread of the pandemic.
Some local governments, including those in Tokyo and Sendai, have been experimenting with sewage surveillance to track the spread of COVID-19.
Since early in the pandemic last year, experts have warned that the official number of confirmed cases could just be the tip of the iceberg as the country had mostly limited giving free PCR tests to those people recommended by doctors or public health centers. Although private companies have made PCR tests affordable and widely available to the public in major cities nationwide, only the more expensive, government-approved tests can be officially used for activities such as travel abroad.
While the number of tests conducted each day in Japan has increased substantially since the outbreak of the pandemic — from a few thousand in early 2020 to more than 150,000 in August this year — the country still lags behind most other industrialized nations.
Still, there are signs of improvement. After nearly two years of criticism that the country isn’t proactively testing enough compared with Europe and other nations, Prime Minister Fumio Kishida said Friday that the government will expand free PCR tests to those who, for health reasons, cannot receive the vaccine. The free tests, he said, would also be expanded to asymptomatic people before taking part in certain economic or social activities when infections are spreading.
While new COVID-19 infections in Japan have been hovering near their lowest levels in recent weeks, the pandemic’s fifth and biggest wave this past summer — which spurred daily nationwide caseloads of nearly 26,000, straining the health care system — continues to serve as a stark reminder of the need to prepare for a possible sixth wave that could hit this autumn or winter.
The new plan floated by Kishida is part of a greater effort to prepare the country for the next wave by offering more support for hospitals, procuring more medical staff, expanding the country’s vaccine campaign, administering booster shots and advancing the treatment of those with COVID-19.
It’s not exactly clear who will be eligible and under what circumstances, but Kishida said Friday that the decision will be left to local governments, who have been directed to execute the plan by the end of next March at the latest.
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