People who received the trivalent influenza vaccine during the 2008-2009 flu season were between 1.4 and 2.5 times more likely to get infected with pandemic H1N1 in the spring and summer of 2009 than those who did not get the seasonal flu vaccine
A double-blind, placebo-controlled study on ferrets confirmed the results, showing the seasonal influenza vaccine did worsen symptoms after subsequent exposure to the H1N1 virus
A 2011 study found the seasonal flu vaccine may weaken children’s immune systems and increase their chances of getting sick from influenza viruses not included in the vaccine
In a 2012 study, children receiving inactivated influenza vaccines had a 4.4 times higher relative risk of contracting noninfluenza respiratory virus infections in the nine months following their inoculation
A 2020 study found people were 36% more likely to get some form of coronavirus infection if they had been vaccinated against influenza
