Japan plans to collect data from people who become infected with the novel coronavirus even after they receive vaccinations to assess how vaccines may help prevent the spread of the virus, sources close to the matter said Sunday.

Inoculations are expected to start in Japan possibly in February. The health ministry will create a system to gather vaccination records of all infected people by adding checkboxes to a document that doctors are required to submit to public health centers when they confirm coronavirus infections, the sources said.

A person receives a shot of vaccine developed by U.S. pharmaceutical company Pfizer Inc. on Jan. 14, 2021, in Madrid. (Getty/Kyodo)

The formats for reporting rubella and measles, other major communicable diseases, also have checkboxes for vaccination records.

The new system will enable authorities to know the immunization records of coronavirus patients, such as which companies' vaccines they have received and whether they had a single or double dose, according to the sources.

Based on clinical trials overseas and their reported efficacy, currently available coronavirus vaccines protect people from getting sick, while whether or not they prevent people from becoming infected is not clearly known yet.

By obtaining information such as the ratio of vaccinated people among coronavirus patients and the progress of their symptoms, the Health, Labor and Welfare Ministry expects it can evaluate the effectiveness of a vaccine and the impact of vaccination on the spread of the epidemic within the country, the sources said.

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Vaccine effectiveness is measured in the real-world setting once a vaccine has been authorized for use in the general population, whereas efficacy is measured in controlled clinical trials, according to the U.S. Centers for Disease Control and Prevention and others, with health experts pointing out that figures for the former may be lower than the latter due to obstacles in such a setting.

Under the law on infectious diseases in Japan, doctors are obligated to inform public health centers of the names of infected people and their symptoms.

The Japanese government plans to begin vaccinating medical workers in late February after a vaccine is approved for domestic use.

Inoculation of nonmedical workers is expected to start in late March, with priority given to people aged 65 or older as they are considered a high-risk group for developing severe symptoms.

Vaccination records of coronavirus patients are also expected to serve as a marker to assess the risk of severe illnesses that would help doctors and health officials determine treatment policies, the sources said.

By keeping the records, authorities may be also able to detect a change in the epidemic situation. They would suspect the potential emergence of a vaccine-resistant variant of the virus if the number of people who get sick does not decrease much even after the dissemination of vaccines.

Japan, with a population of 126 million, has supply agreements with pharmaceutical companies Pfizer Inc. and AstraZeneca Plc for 120 million vaccine doses from each, as well as a contract with Moderna Inc. for another 50 million doses.