Photo/Illutration A health care worker receives the third shot of COVID-19 vaccine in December 2021 in Hachioji, western Tokyo. (Asahi Shimbun file photo)

The health ministry initially misclassified people in its COVID-19 vaccination data with some listed as unvaccinated although their status was unknown, which likely led to exaggerating the effectiveness of vaccines.

Until May 11, the ministry had counted people whose COVID-19 vaccination history was left blank in the ministry’s system as "unvaccinated."

Data from April 11 to 17 that the ministry released on May 11, however, now shows such people being counted as “COVID-19 vaccination history is unknown.” There are now four groups represented: unvaccinated, vaccinated twice, received the third shot, and vaccination history unknown.

"There was no intention to exaggerate the number of COVID-19 patients who were unvaccinated,” said a ministry representative.

A panel of experts who advise the government regarding infection measures released the data to the public.

Outside sources pointed out the misclassification to the ministry, who then changed their calculation methods.

Since the data was corrected, the number of people who are both unvaccinated and newly infected with the novel coronavirus has significantly dropped.

The ministry’s data has been used as an analytic tool to show the effectiveness of vaccines.

The revelation indicates the ministry poorly handled the data it received. 

The documents released before May 11 had shown a trend that among the number of newly infected patients, there were more unvaccinated patients than patients who had been vaccinated in all age groups.

Takaji Wakita, head of the National Institute of Infectious Diseases who chairs a panel of experts advising the health ministry, was asked about the significance of the third shot during a news conference on April 13.

Wakita said, “If you look at the data, it is obvious. By progressing from the unvaccinated to those vaccinated twice to those vaccinated three times, the number of new patients decreases, and the vaccines prevent infections from spreading.”

A senior official of the Cabinet Secretariat also said at a news conference on April 20 that the data “shows a certain trend.”

The ministry said local governments and health care organizations have input information about COVID-19 patients in the ministry’s system.

Initially, however, there were not many new COVID-19 patients who had received a vaccine.

Thus, the ministry counted people whose vaccination history was left blank as “unvaccinated” and continued doing the same afterward.

“It was to relieve the burden on those who gave us the input," said the ministry representative. 

Regarding the credibility of the data released before the change of the method, the representative said, “The data was collected to see the number of people with ‘breakthrough infections’ and is not an indication of the effectiveness of COVID-19 vaccines.”

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The Asahi Shimbun

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