Why do people seem to feel worse after the second vaccine than the first?

Not speaking from personal experience. Not yet, anyway.

My mother’s first vaccine shot didn’t bother her very much, but her second one hit her like a ton of bricks, taking several days to fully recover from. She felt muscle aches and great fatigue.

The fully-vaccinated people I’ve spoken to have all had worse symptoms after the second vaccine than the first. What gives?

This has been answered in several of the Covid/vaccine/vaccination threads extant here.

One shot of iron,
The second of steel:
If the first one doesn’t get you
Then the next one will!

I would still argue it would be good to answer it here. A thread asking a direct question is the sort of thing that people are most likely to find in a search.

Also, while I’ve speculated myself, and seen other speculation, I can’t remember seeing any definition answers, despite reading a whole lot of these threads.

It was described to me that after the first shot, the immune system says…crap, what’s this stuff. Better clean this up right away. So it starts making antibodies and “knocks out” the invader. Then when the second shot comes, the immune system says…holy shit, this again! We’re under attack, this is no fluke, time to bring in the big guns.

Since the crappy feeling you have is in most cases a reaction not to the infection but instead the body’s response to the infection, when you get a much bigger, much more aggressive response the second time you feel a lot worse.

So what does it mean when you don;t have much of a reaction? I had the J&J shot which, granted is one and done so the reaction profile is probably different than when getting two shots, but I didn’t really feel much of anything other than a sore shoulder. Maybe the slightest bit of tiredness and chills the rest of the day that I got the shot, but it could have been my imagination since I was monitoring myself for any reaction. I wonder whether my shot was effective or not.

The immune system reacts anamnestically.

I’m not a doctor, so this is just me passing along what I was told.

The reason that some people have a worse reaction than others has to with the relative strength of their immune systems. Data has shown that younger people and women tend to have more severe side effects than older people and men respectively. The idea being that young people’s stronger immune systems react harder and make them feel worse.

For any given person there’s going to be variability in how intensely they react. What I don’t know is if there’s any relationship between the severity of the side effects and the individual effectiveness of the immunity. I suspect not. Also not sure exactly why the mRNA type ones require 2 doses and the traditional ones do not. They supposedly have a lower overall effectiveness so there may be a correlation.

Several immunologists and infectious disease experts interviewed by MedPage Today said there are no data that a reaction correlates with protection.

The spouse had the first Pfizer shot with no notable reaction. I had the first AZ shot which knocked me on my ass for a day.

Friends who have had their second shots have said that the second Pfizer hit them harder than the first, but the second AZ one was quite mild compared to the first. So perhaps it depends on which vaccine you get.

All of the above is entirely anecdotal.

Look at you with the new word-of-the-day calendar. :wink:

I got Pfizer. First shot had a significantly more profound impact on me than the second shot. First shot was a pretty sore arm for 48+ hours and flu-like symptoms the first 24 hours. Second shot was zero local reaction to the shot and just a mild feeling of fatigue in the early evening of the same day. I was expecting the reverse in line with what you posted, but it was in contrast to my personal anecdotal experience.

Pfizer. The second hit me harder. Sore arm for both, fatigue the first time, headache, body aches and more fatigue the second. Neither one severe, though.

I give 50/50 odds my second shot was saline. The urgent care clinic that gave me the shots looked sketchy as fuck.

Wait 2 weeks then get an antibody test. If you were given placebo call you local TV station muckrakers; they’d love to hang somebody out to dry. Also call the CDC.

I’m with @LSLGuy

If you were part of a study and could potentially get a placebo you’d know it and would have agreed to it.

If you were just Joe Schmo walking in off the street expecting a real vaccine then you should have gotten a real vaccine. If they tricked you and gave you a placebo I am willing to bet you are the future winner of a huge lawsuit.

I’m not suggesting a formal placebo as in a trial.

I was trying to say that if the poster actually reasonably beliieves he got something fake he should act on that suspicion, not just whine ineffectually to us here. And if he can’t be arsed to take his contention seriously, there’s not much reason I/we should either.

Not quite “put up or shut up”, but close.


I was being facetious not being a fucking whiner. The urgent care clinic was a bit sketchy but I probably got what I came for. I was simply commenting on the fact that while most people tended to have a more serious reaction to the second shot, mine was worse after the first shot and virtually unnoticeable after the second. I see no reason to call Dewy, Sue’em and How.

Christ. Who’s over-reacting here?

Et tu?..

Here is a good explanation by a doctor about why the second dose knocks out people more than the first: