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Among people aged 65 years and older, flu vaccination was positively associated with COVID-19 deaths, meaning those who got a flu vaccine were more likely to die from COVID-19.

A May 2020 analysis by online news publication The Gateway Pundit similarly found that European countries with the highest COVID-19 death rates had high rates of flu vaccination — at least 50% — among the elderly.

Previous coronavirus vaccines have been linked to enhanced disease; it's suggested flu vaccination could potentially contribute to COVID-19 via pathogenic priming, a scenario in which, rather than enhancing your immunity against the infection, exposure to a vaccine results in more severe disease.

Given the increasing research suggesting flu vaccination may worsen viral illness, flu vaccines should be evaluated as potential causative agents or, at least, contributors to the COVID-19 pandemic.

For years, concerns have been raised that previous flu vaccination seems to increase patients' risk of contracting more severe pandemic illness. This occurred during the 2008 to 2009 flu season, when prior vaccination with the seasonal flu vaccine was associated with an increased risk of H1N1 "swine flu" during spring/summer 2009 in Canada.

A January 2020 study published in the journal Vaccine also found people were more likely to get some form of coronavirus infection if they had been vaccinated against influenza during the 2017 to 2018 flu season.

Compared to unvaccinated individuals, those who had received a seasonal flu shot were 36% more likely to contract unspecified coronavirus infection (it did not specifically mention SARS-CoV-2, the coronavirus that causes COVID-19) and 51% more likely to contract human metapneumovirus infection, which has symptoms similar to COVID-19.