You can't get influenza from a flu shot

June 25, 2019 by Allen Cheng And Katherine Kedzierska, The Conversation
You might feel a bit off after your flu shot but this doesn’t last long. Credit:



But while you might sometimes get sick after having a flu shot, it's a myth that having a flu shot can give you the flu.

A quick history of the flu vaccine



The process to produce modern influenza vaccines now occurs on a much more refined and industrial scale. Hundreds of thousands of are collected by hundreds of national influenza centres around the world.


Most modern vaccines are manufactured by growing large quantities of live virus—mostly in chicken eggs or less commonly animal cells—which are then purified, deactivated and split into smaller components. These vaccines are inactive and cannot replicate.

There are also two new "enhanced" vaccines that are used in older people, who don't tend to respond as strongly to vaccines: Fluzone High Dose and Fluad, which is designed to better stimulate immunity and draw to the site of vaccination.

How the immune system fights the flu

The human immune system has several strategies to protect against infection. For viral infections such as influenza, the key strategy is known as adaptive immunity. This part of the immune system can "remember" previous exposure to pathogens.


T lymphocyte cells of the immune system can recognise this viral incursion. T cells protect against further spread of the virus by activating pathways that cause infected cells to trigger a "suicide" process.


Modern flu vaccine development is slow and labour-intensive process. Credit: hotsum/Shutterstock

Flu shots help mount a quicker defence


Influenza vaccines harness this arm of the immune system, known as "humoral" immunity. By "practising" on viral components, vaccines allow the immune system to react more quickly and effectively when faced with the real virus.

So why do you sometimes get sick after a flu shot?




Third, vaccine-induced protection isn't complete. In some years, the vaccine is not well matched to circulating strains. Usually this is due to mutations that may develop in circulating strains after the vaccine strains are selected.

The flu vaccine also doesn't "kick in" for two weeks after vaccine administration. In some people, particularly those who are older and those who have weakened immune systems, antibody production is not as strong, and the level of protection is lower.

Despite this, studies have consistently shown that vaccinated people are less likely to get influenza or complications from the flu than those who aren't vaccinated.

A better way to protect against the flu


Current work is aiming to speed up this process by using different technologies so that manufacturers can react more quickly to changes in circulating viruses.

The "holy grail" for influenza vaccines is to stimulate an effective immune response to a component of influenza that doesn't change each year, so annual vaccination is not required.

These efforts have proved elusive so far.

A better strategy might be to harness T cell immunity. Recent work has shown that a type of T cell, known as "killer" T cells, can recognise other parts of the , and therefore can provide broad protection against seasonal and pandemic strains.


Provided by The Conversation
