no ill effects after second Moderna shot - does it mean anything?

March 26, 2021 7:38 AM

I had my second Moderna shot last night and feel completely normal. Does this “mean” anything about the strength of my immune system?

I’m a woman in my late thirties, reasonably healthy (I think?!). Almost everyone I know around my age felt awful for a little while after their 2nd vaccine. I was basically assuming this would happen to me too, but it’s been over fourteen hours now and aside from a sore arm again I feel fine. I’d always heard that feeling sick after means you have a robust immune system and that that is why older people often suffer no ill effects. I’m not...disappointed per se? But do wonder what if anything it “means.” Is my immune system not as strong as I thought? I’d love to hear from people who really understand the science behind this!

posted by cakelite to Health & Fitness (21 answers total)

This is complete anecdata, but most people I know had their reactions to the second dose start 24-48 hours after the shot (Pfizer and Moderna), and felt fine until then. At 14 hours, you may just not be in the window yet.
posted by okayokayigive at 7:46 AM on March 26, 2021 [6 favorites]

I don’t think it means anything if you don’t feel ill, but I can say it was definitely a full 24 hours until the systemic sick feeling kicked in for me.
posted by obfuscation at 7:48 AM on March 26, 2021

Response by poster: Last comment I promise:

Everyone I knew felt something come in within eight to twelve hours. But I take your point that my very small pool doesn’t mean much!

I question this article because while it says that fifty percent of people who get the vaccine don’t have side effects, I think the majority of people getting it at this point are above fifty and they seem less likely have have side effects in the first place.
posted by cakelite at 7:50 AM on March 26, 2021

Just another data point - I had my first Pfizer shot yesterday and feel dreadful today.
posted by 41swans at 7:55 AM on March 26, 2021 [2 favorites]

Anecdata: I'm also in my late 30s, and was wondering the exact same thing ~12 hours post shot. I felt fine! Yay!

Yeah, about 24 hours after the shot I felt a lot less fine. Kind of flu like and exhausted for 2 days.

During my "I feel fine!" stage I did some research on this exact thing and in trials only ~50% of folks had side effects to the second dose, and I couldn't find any clear reasons for what would cause someone to have them vs not.

Congrats on getting vaccinated!
posted by nancynickerson at 7:56 AM on March 26, 2021 [2 favorites]

If you are looking for data points, my healthy 43 year-old husband had nothing but a sore arm after his second Pfizer shot.
posted by Pax at 7:57 AM on March 26, 2021 [2 favorites]

As a health care worker I was able to get the vaccine early on, as did most of my co-workers. Reactions to both the first and second shots ranged from "my arm was a little sore" (which was my personal experience) to "I almost called in sick the next day I felt so bad." Presumably most of us are protected. although the only way to know for sure is to look at antibody titers (or intentionally try to infect ourselves). So the side effects seem to vary a good bit.
posted by TedW at 8:00 AM on March 26, 2021

No. A lack of systemic side effect doesn't mean your immune system isn't responding.

About 55% of folks who got the Moderna first dose reported systemic side effects which means 45% did not. And 80% after the second, which means 20% did not.
posted by Geckwoistmeinauto at 8:01 AM on March 26, 2021 [1 favorite]

Best answer: The point I meant to make in the previous statement was that even if 20% of people did not have systemic side effects after the second shot, we see protection in way more people than if not feeling anything from the second shot said it didn't work. Basically, if not feeling shitty meant your shot didn't do its jobs, scientists would have seen it in the efficacy data.
posted by Geckwoistmeinauto at 8:03 AM on March 26, 2021 [9 favorites]

Best answer: Epidemiologist here. Your subjective physical experience after a vaccination is functionally meaningless and not an indicator of your immune response nor your protection from infection. I could say a lot more, but the summary is that we still don't know all the details that inform why the physiology of immune response seems to be so idiosyncratic.

I had a two day fever and full body aches after each of my doses of Moderna. My labmate felt nothing. Same vials of vaccine, same administration days, two bodies, nothing's shocking.
posted by late afternoon dreaming hotel at 8:18 AM on March 26, 2021 [37 favorites]

Best answer: Honestly, I think the whole "if you feel sick, it means your immune system is responding!" is a successful public relations campaign to encourage people to get the vaccination despite the side effects.

How many people do you know who say, "I don't get the flu vaccine because it makes me sick / I heard it makes you sick"? We could have easily seen the same effect for this vaccine—but widespread covid vaccine refusal would be catastrophic.

The covid vaccination seems to make more people feel sick than the flu shot, and they did a masterful job getting out in front of that to turn the sickness into a feature, not a bug.
posted by BrashTech at 8:21 AM on March 26, 2021 [25 favorites]

Best answer: The most likely explanations:
- you're one of the lucky ones whose immune systems was just like, "okay, I'm on it!" and took care of business with no complaints
- behind you looms a wrecking ball and half a day from now you're going to be writing another question like "would I feel so shit if I hadn't said anything?"
- a week from now you'll realize actually, I kinda did feel like crap but it was overshadowed by *gestures around* but now I'm definitely 100%, funny how perspective works

There's been enough delivered vaccinations at this point that the data would show it if it actually wasn't working. There have been some anecdata and news stories about people getting sick in between rounds (some of whom were likely already incubating at the time they got their first shot), but very little has come up so far about post-second-round/post J&J.

That's even potentially worrisome, especially in light of variants, as it encourages higher-risk return to activity than is appropriate. This may mean people are getting mildly sick post-vax (as intended!) and not reporting or assuming it's a cold or allergies, and not considering their potential to spread a new variant. But incidences of very obvious covid or hospitalization in fully-vaccinated people are not happening like you'd see if even a small percentage got little to no protection.
posted by Lyn Never at 8:25 AM on March 26, 2021 [4 favorites]

Also consider selection bias in who you are hearing from about this. People who don't have side effects might not mention their shot to you at all.
posted by ewok_academy at 8:49 AM on March 26, 2021 [7 favorites]

Everyone I've heard from who had side effects to the second shot, they got them the next day.

The strength of those side effects ranged from a teacher friend who had a few aches and lethargy the next day, to a friend who woke up early the following day feeling great and then after one hour of energetically doing stuff, suddenly felt sleepy and laid down "for a catnap" that lasted seven hours, to someone in my physical therapist's office who just had a sore neck, to one of my two physical therapists who started feeling rough mid-day and actually took off right when I showed up for our appointment (he waited around until I showed up, asked me if I'd had any pain in my injured knee, and when I said "no" he said "great - I had my second shot yesterday and I feel like crap, here's my intern Nicky, he'll take over for me today" and he left).

Ages of all people concerned ranged from 20s to 50s, in varying levels of health. But in all cases the side effects didn't show up until the following day.
posted by EmpressCallipygos at 8:59 AM on March 26, 2021

For another anecdote: 24 hours to the minute from my 2nd I felt like I got hit by a bus. I had felt pretty cocky about not having any side effects until that. Felt very bad for about 12 hours.
posted by gryphonlover at 10:02 AM on March 26, 2021

Just to contribute to all the anecdotes...

I got my second dose on Monday and had zero side effects. Nor did probably 80% of my friends who have had their two shots. My husband was the worst, and he had a mild body ache. So if I were looking at my friend group to make assumptions, I'd assume that side effects were rare (I know that isn't true).

You're fine.
posted by gaspode at 11:49 AM on March 26, 2021

Best answer: I got my second shot on Tuesday and essentially had no side effects. Kind of tired and lack of appetite 24 hours afterwards, but that's it. I really wanted to feel *something* and have also been having anxiety about it, so you're not alone. :)
posted by findabair at 11:59 AM on March 26, 2021

I had my first Moderna shot a week ago Tuesday, and by the evening had spiked 2.5 degree fever (for me) that persisted a full week. I also was exhausted and everything ached, even my hair. That tapered off over the weekend, but it was still 5-6 days of ugh. My arm did not hurt more than any other part of me, though.
Everyone else I know got the Pfizer so I don't even have anecdata to compare to; the stats Geckwoistmeinauto mentioned above are good to know, I feel like less of an outlier now.
posted by ApathyGirl at 12:52 PM on March 26, 2021

I had the same reaction to my second Moderna shot, which is to say, nothing. Only the tiniest bit of feeling at the injection site. No side effects after my first shot, either. I've had flu shots that hurt worse.

Because I have Crohn's disease, am in my 60s, and have been on a series of immunosuppressant medications for years, each more powerful than the last, I'm concerned that my immune system may be so tamped down that I too am wondering about Covid vaccine efficacy. There are a couple of articles I've found in gastroenterology journals that are posing that question as well; the short answer seems to be that nobody knows yet.

I've signed up for a study at UNC-Chapel Hill designed for people with IBD who have received the vaccine. I've only had the initial email screening but hope to be included in the full study, which will include an antibody test. In the meantime, I'm following the same protocols to avoid Covid exposure as when I wasn't vaccinated.
posted by apartment dweller at 6:59 PM on March 26, 2021

Response by poster: Thanks guys. I ended up sleeping a lot today, and I’m guessing I’ll feel 100% tomorrow. You all made me feel a lot better!
posted by cakelite at 7:09 PM on March 26, 2021 [1 favorite]

After my first Pfizer shot I had some muscle soreness for a few days (not just around the injection site). About 24 hours after the second shot I had a low grade fever, tiredness, and generally didn't feel that great. By the next morning, after a very deep night's sleep (why can't I sleep like that every night?) I woke up feeling perfectly normal...not even the muscle aches I had after the first shot, though I still have a ghost of a pain at the injection site a week later.

My wife had no after-effects from either shot (but, as she says, she's tough). My youngest son, who has several conditions that make him eligible for shots, had his first Moderna shot yesterday and is feeling headachy today, with other muscle pain.

I think these anecdata show that the reactions vary widely from person to person, and past performance doesn't predict future results.
posted by lhauser at 1:13 PM on March 27, 2021