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Information on Adverse Events Following Seasonal Influenza Vaccination

Information on Adverse Events Following Seasonal Influenza Vaccination
The 2020/21 egg-based quadrivalent seasonal influenza vaccine contains the following:
  • an A/Guangdong-Maonan/SWL1536/2019 (H1N1)pdm09-like virus
  • an A/Hong Kong/2671/2019 (H3N2)-like virus
  • a B/Washington/02/2019-like virus
  • a B/Phuket/3073/2013-like virus

If trivalent influenza vaccine is being used, the influenza B component shall contain a B/Washington/02/2019-like virus.

Seasonal influenza vaccine is very safe and usually well tolerated apart from occasional soreness, redness or swelling at the injection site (inactivated vaccine).  Some recipients may experience fever, muscle pain, and tiredness beginning 6 to 12 hours after vaccination and lasting up to two days.

An adverse event is a health problem that is reported after someone gets vaccinated. It may or may not have been caused by the vaccine.  Some of these events may occur by chance during the post-vaccination period and are unrelated to vaccination. Report of adverse event does not mean that a vaccine caused the event.

Number of GBS (within the period of 5 days and 6 weeks after vaccination) and other serious neurological adverse events reported among vaccinated person in 2020/21 season (as of 12 noon, 21 February  2021):

Guillain-Barré Syndrome

Other serious neurological adverse events



For the number of newly admitted GBS cases in Hong Kong, please click here.