5. Temporary Exacerbation of Underlying Conditions (Very Rare)
In people with chronic health conditions — like autoimmune disease, asthma, heart disease or diabetes — there is a very small chance the flu shot might temporarily “stir up” their system. While it’s far better to be protected (especially in these groups), being informed helps.
What to watch for
- Slight worsening of asthma symptoms for 1-2 days after vaccination.
- Mild flare of autoimmune condition (joint ache, fatigue) shortly after the shot.
- Increased heart rate or palpitations in those with cardiac conditions (rare).
Why it happens
The immune system is stimulated — and in people whose baseline is fragile, that stimulation can show up more noticeably. Importantly — getting the flu itself poses a far higher risk, including hospitalisation or death.
What to do
If you have a pre-existing condition, talk to your provider before the vaccination and ensure your health insurance plan covers any unexpected treatment costs.
Monitor symptoms for a few days. If things worsen significantly, your plan might offer virtual monitoring or in-network urgent care visits.
Use your health savings account (HSA) or plan’s preventive-care benefits to reduce cost-barriers.
