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The purpose of this trial is to examine whether the combination of the trial flu vaccine together with the existing seasonal flu vaccine will:
a. better protect older adults from flu-like illness and,
b. reduce the severity and duration of flu-like symptoms
than the current flu vaccine alone.


Flu and older adults

Flu is a commonly used term that refers to different influenza viruses and strains that are highly infectious. Flu occurs every year and can affect anyone. 

However, some groups of people are more likely to get it, and may feel more unwell, if they do. One of these groups are older adults. In this age group, current vaccines are less effective than for other at risk groups. And so as the need for a new vaccine that is effective is much higher in this group, we will be recruiting adults 65 years and over to test the INVICTUS trial vaccine.

Current Vaccine

Existing flu vaccines use ‘surface proteins’ from the outside of the flu virus that stimulate your immune system to produce antibodies. These antibodies protect you from getting sick with the strain of flu virus or viruses whose ‘surface proteins’ you were injected with.

As the seasonal flu virus changes its ‘surface proteins’, the flu vaccine needs to change too. This is so your body receives the new surface proteins and is able to produce the relevant antibodies that will protect you- from the changed flu virus.

This means that with the current vaccine you are only protected against the flu virus(es) your body has antibodies for.

The current vaccine, given before the flu season starts, is based on a prediction of the strain of flu that will be circulating for that flu season.

Trial Vaccine

The trial flu vaccine consists of two proteins from the ‘core proteins’ of the flu virus and a vaccine delivery system. This new vaccine stimulates a different part of your immune system called  T - cells. We have found from previous research studies that T - cells fight flu viruses that your body has no antibodies for and can reduce the severity of your symptoms as well as the time you have been experiencing them.

So even if you did get a flu virus you do not have antibodies for, the trial vaccine could still offer you protection from severe illness.

Also, as the ‘core proteins’ of the flu virus(es) remain virtually unchanged every flu season, the immune response your body elicits upon receiving the trial vaccine might be able to better protect you from many different flu strains even if they do change their ‘surface proteins’ periodically.


Study Design: Phase IIb randomised controlled, participant blinded clinical trial
Sponsor: Vaccitech
Ethical Approval: 17/SC/0300
Contact Details:
Chief Investigator: Professor Chris Butler

take part

Click here for more information about how to take part in this study.

Trial management:


Dr Tom Evans

Chris Ellis