Has influenza exceeded the alert level in Japan because 80 percent of the population have a weakened immune system due to COVID-19 vaccination? No, that's not true: One of the reasons for the high influenza level is a decline in herd immunity to influenza.
The claim appeared in a video on TikTok on December 19, 2023, by user6144061382609. It began (translated from Japanese to English by Lead Stories staff):
Trend as Planned
80% of the population has weakened immune system
Influenza alert level exceeded. Fastest in the past 10 years - excerpts from Yomiuri newspaper
This is what the post looked like on TikTok at the time of writing:
(Source: TikTok screenshot taken on Tue Dec 25 11:49:31 2023 UTC)
The TikTok user also posted (archived here) the following claim (as translated): "There is a risk of death from influenza due to reduced immunity after vaccination. ... Immune function is impaired by the coronavirus vaccine."
In September 2023, an influenza epidemic advisory was announced in Tokyo. Media outlets such as the Sankei newspaper (archived here), Yahoo News (archived here) and Yomiuri News (archived here) indicated a weakened immune system as the cause of the flu outbreak. The media pointed to a decline in herd immunity, as influenza had not spread in 2020-23 due to the measures taken to prevent the spread of the coronavirus.
The Ministry of Health, Labour and Welfare explained herd immunity as: "If more than a certain percentage of the population is immune to a particular pathogen, even if an infected patient is found, it will be difficult to infect others, preventing the spread of infectious diseases and indirectly developing immunity. People without immunity are also protected from infection. This condition is known as herd immunity, and society as a whole is protected from infectious diseases."
The Japan Broadcasting Corporation NHK explained the decline in herd immunity to influenza as (as translated):
If we look at the percentage of people with influenza antibodies by age group, for example, in 2018, for a particular type of influenza A, the percentage of people aged between 5 and 19 who had antibodies was over 70%. In 2023, however, the quota of the same type will be less than 40%. Children generally have less contact with pathogens than adults due to their younger age, so their immune system is less developed. As children get older, they gradually strengthen their immune system as they come into contact with many viruses and pathogens. However, since the outbreak of the coronavirus, there have been two seasons in 2021 and 2022 with almost no flu outbreaks. As a result, the antibody prevalence rate among young people is low.
