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Everyone receiving the COVID vaccines is asked to wait for 15 minutes in case they have a bad reaction to the shot. Given that we've now had hundreds of millions of Pfizer vaccine shots injected around the world, is there any data showing how many of those people end up needing medical attention during those 15 minutes (possibly 20 minutes in some areas, as reported in comments)?

If such data is available, do we know how many of those people ended up needing attention because of the vaccine itself? I.e. if you take any random 15 minute period, around 23 Americans will get a heart attack during that time, so logically speaking not all cases of medical problems during the 15 minute period will be caused by the vaccine itself.

Note that I'm only interested in that exact 15-minute waiting period, not any other side effects from the vaccine that are detected later on. I.e. myocarditis is suspected to be linked to the COVID shot for some people, but that's usually detected later on, not during the 15 minute observation period.

JonathanReez
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  • Just yesterday night I thought to post this in MedicalS.SE! – NotStanding with GoGotaHome Nov 09 '21 at 06:38
  • If you're thinking of exactly 15 minutes, do you want data restricted to countries where the wait is 15 minutes? Or even restricted to the US? (When I had mine in the UK I had to wait for 20 minutes before leaving) – Chris H Nov 09 '21 at 15:44
  • @ChrisH excellent point! i didn't know it was 20 minutes in the UK, question updated. I'm interested in the period during which people are advised to stay in the clinic/vaccine site, whatever that period is. – JonathanReez Nov 09 '21 at 19:11
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    @chrisH @johmathanReez that’s not standard for the U.K. it’s 15 minutes. Not sure why Chris had to wait 20. https://www.nhs.uk/conditions/coronavirus-covid-19/coronavirus-vaccination/what-happens-at-your-appointment/ ` – Tim Nov 09 '21 at 19:50
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    @Tim I have a feeling it was 20 for the first dose (May), 15 for the 2nd (July), so maybe the guidance changed. I know the myocarditis worry came along about the time of my 2nd dose, because I had a massive bike ride starting 49 hours after it. – Chris H Nov 09 '21 at 20:52
  • @ChrisH ahh potentially. It was 15 for both of mine (July, August) – Tim Nov 09 '21 at 20:53
  • @ChrisH: The guidance did not change as far as I can tell. You got a different observation period depending on how you filled the form. – Joshua Nov 09 '21 at 21:30
  • @Joshua that may also be true, though it would have to have been done fairly subtly based on what I saw - and everything was so smooth and fast at the mass vaccination clinic that as much as possible was done verbally rather than by stopping to fill in paperwork. Or maybe it was even rounding error such that the observation period was minimum 15 minutes, specified to the next 5 minutes. But I didn't mean to distract the discussion, rather to clarify the variable – Chris H Nov 10 '21 at 08:26
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    This is anecdotal, so not worth a whole answer, but when I helped a friend of mine get her shots, I asked the attending nurse specifically this question while waiting. In this case, they were doing them in a tent, outside, in the midday Florida summer heat. Nearly all of the people who needed medical attention were simply cases of heat exhaustion from being forced to wait outside for that long. My own shots were thankfully done indoors, in an air-conditioned pharmacy. – Darrel Hoffman Nov 10 '21 at 18:20
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    @JonathanReez If you want to make alarming claims, you need to bring convincing evidence. Comments here aren't a discussion forum. – Carey Gregory Nov 11 '21 at 06:45

3 Answers3

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The most noteworthy complication, and most heard about in the news, is anaphylaxis.

This article breaks down cases of anaphylaxis nicely: Reports of Anaphylaxis After Receipt of mRNA COVID-19 Vaccines in the US—December 14, 2020-January 18, 2021. They provide a great table with a specification of whether the case happened during the 15-minute window:

enter image description here

So for Pfizer specifically the numbers are:

  • 4.7 anaphylaxis cases per million in total
  • 3.6 cases per million if only the 15 minute window is considered
  • 1.1 per million for those without a prior allergic reaction to a drug or vaccine

This doesn't account for non-anaphylaxis allergic reactions (more common, less severe), vasovagal syncope(fear of needles/injections), or any other, more rare conditions.

To date data regarding medical attention received within 15 minutes of vaccination has been hard to come by. The data from the first week of Pfizer administration, covering some 1.8m patients shows that non-anaphylaxis allergic reactions were roughly 8 times more common (and typically far less severe) than anaphylactic reactions.

While we could attempt to extrapolate based on anaphylaxis cases and non over the year based on the first week's data, it'd be a relatively pointless exercise. The occurrences/million for anaphylaxis dropped from 11.1 to 4.7 in the time frame. We can't assume the reduction in case numbers to be proportionally identical, yet a simple extrapolation based only on time would be disingenuous.

In short, reliable data on the topic outside anaphylaxis is hard to come by because other instances requiring medical attention are either less severe or less common.

TCooper
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JonathanReez
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    I wonder where the massive gender imbalance comes from - it's unlikely to be reporting bias for something serious happening under observation – Chris H Nov 09 '21 at 15:47
  • What about anything(everything) other than anaphylaxis? – TCooper Nov 09 '21 at 23:15
  • @TCooper seems like anything else would not be vaccine related? – JonathanReez Nov 09 '21 at 23:18
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    The question doesn't ask "What side effects has the vaccine caused?" It's "How many people end up needing medical attention during the 15 minutes window after receiving the Pfizer vaccine?" Do you really think no one fainted as the needle came out and received medical attention, just from a fear of needles? Just one example; this is clearly a good, but incomplete, answer. – TCooper Nov 09 '21 at 23:29
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    @TCooper but those effects would be present even if you injected a saline solution into each patient. Other effects (like random heart attacks) would be present even if you didn't inject anything at all and just had people sit in a room for 15 minutes. If you know of a good paper that takes this into account, I'm happy to see the answer! – JonathanReez Nov 09 '21 at 23:31
  • You seem to be stuck on the vaccine as the cause, which again, is not what this question asks. But even from your perspective of "only-caused-by-the-vaccine" your answer is incomplete. See here: https://www.cdc.gov/mmwr/volumes/70/wr/mm7002e1.htm for 83 cases of nonanaphylaxis allergic reactions coinciding with the 11 recognized in the first week of administration. The median onset time was 12 minutes with 85% happening within 30 minutes. That link also states "Nonallergic adverse events, mostly vasovagal or anxiety-related, were excluded from the analysis", implying their existence. – TCooper Nov 09 '21 at 23:40
  • To my point about caused by the vaccine or not - everything recorded in VAERS very clearly isn't caused by the vaccine that was just administered. We can, should, and do still record those events. We also interpret the data knowing those events are present within it. I don't have a more complete answer - why I'm commenting to try and improve this one, as I think its a good start, but needs more details. – TCooper Nov 09 '21 at 23:46
  • After searching my biochemical knowledge I have come to the conclusion that the data showing Anaphylaxis gender imbalance at that extreme rate of 94% means the data is not trustworthy. – Joshua Nov 10 '21 at 02:25
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    @Joshua: What biochemical 'knowledge' did you search? A quick google search brings up this paper that says "One possible explanation for the sex imbalance is that sensitization to PEG is more common in women due to the relatively frequent exposure to PEG-containing products, such as cutaneous exposure to cosmetics or the use of medications such as contraceptive injections.". Whether it is correct or not is not my point; you shouldn't anyhow claim that the data is not trustworthy without evidence against it. – user21820 Nov 10 '21 at 07:43
  • @user21820 Thanks, that's interesting because my more general (i.e. without "covid") search didn't help quickly and I didn't have time for a better look – Chris H Nov 10 '21 at 08:27
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    @ChrisH: Actually I searched for "anaphylaxis women vaccine", not even "covid", and it was the 4th result. I emphasize that I do not know whether it is reasonable to believe the hypothesis in that paper, but unless there is good evidence against it we should consider it plausible. That is, differences in behaviour may contribute to measurable physiological disparities. – user21820 Nov 10 '21 at 08:32
  • @user21820 I can't remember my exact term, but anyway that paper is an interesting read – Chris H Nov 10 '21 at 08:48
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    @ChrisH I suspect a significant part of the observed gender imbalance is because this is based on data only up to mid-January 2021. That and the age range suggests that these were mostly vaccinations of nurses and other (health)care personnel, where women tend to be overrepresented in general. To draw any conclusions wrt gender imbalance, we would have to examine risk ratios (events normalized to number of doses administered per gender). – TooTea Nov 10 '21 at 10:47
  • @TooTea not over-represented to the extend of 90%+, but that would certainly contribute. The paper user21820 uses a different dataset and has 63% of doses administered to women, but ~95% of anaphylaxis cases. They don't state risk by gender explicitly and without following the citations there isn't quite enough information to work it out – Chris H Nov 10 '21 at 10:54
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    @ChrisH: I can't account for it either, but the initial report for blood clots in J&J showed 100% females affected, which also turned out to be bad data, as in not suitable for further induction. – Joshua Nov 10 '21 at 15:12
  • @Joshua my Google-fu isn't strong enough to find better data, I'd be happy if you have better sources, as I don't have a way to improve my answer otherwise – JonathanReez Nov 10 '21 at 19:25
  • @TCooper happy to incorporate any reliable sources into my answer, sadly my Google-fu isn't finding anything better. Please share some links and I'll do it :) – JonathanReez Nov 10 '21 at 19:26
  • @JonathanReez I'll try to find something later if I can. I added a suggested edit just based on the link I posted in above comment / imo changing the wording to provide the information available, but allow for the unknown information to be acknowledged simultaneously. If you don't like whole thing and want to reject, but want to use any part, please do – TCooper Nov 10 '21 at 19:45
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The data on this aren't hard to find. Here are some more examples that specifically provide time frames to back up @A Rogue Ant's answer:

For the Pfizer vaccine:

During December 14–23, 2020, monitoring by the Vaccine Adverse Event Reporting System detected 21 cases of anaphylaxis after administration of a reported 1,893,360 first doses of the Pfizer-BioNTech COVID-19 vaccine (11.1 cases per million doses); 71% of these occurred within 15 minutes of vaccination.

And for Moderna:

During December 21, 2020–January 10, 2021, monitoring by the Vaccine Adverse Event Reporting System detected 10 cases of anaphylaxis after administration of a reported 4,041,396 first doses of Moderna COVID-19 vaccine (2.5 cases per million doses administered). In nine cases, onset occurred within 15 minutes of vaccination. No anaphylaxis-related deaths were reported.

In both studies, 70-90% of anaphylactic reactions occurred within the first 15 minutes, hence the 15-minute protocol.

Carey Gregory
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  • Besides that, there are the unlucky bastards like me who suffer from a medical condition called Vasovagal syncope who tend to faint after an injection, but that's any injection and not only Covid vaccines – Juliana Karasawa Souza Nov 09 '21 at 10:38
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    Why is all the data specific to anaphylaxis? What about other side effects? – Barmar Nov 09 '21 at 15:44
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    @Barmar Like what? They report the side effects that actually occur. – Carey Gregory Nov 09 '21 at 15:51
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    I guess I find it hard to believe that there have been no other types of adverse reactions? – Barmar Nov 09 '21 at 15:53
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    @Barmar What other types of adverse reactions would you expect? – RBarryYoung Nov 09 '21 at 15:54
  • @Barmar Why is it hard to believe? Do you think the same thing about the flu vaccine? – Carey Gregory Nov 09 '21 at 15:57
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    @RBarryYoung The question mentioned heart attacks. Anxious people may have panic attacks. – Barmar Nov 09 '21 at 15:57
  • The data's junk. The people doing the monitoring weren't doing their jobs. Source: personal observation on site. – Joshua Nov 09 '21 at 15:58
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    @Joshua Calling data junk based on your anecdotal experience is also junk. – Carey Gregory Nov 09 '21 at 15:58
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    If I knew a way to improve the situation I would do so. – Joshua Nov 09 '21 at 16:02
  • @joshua are you claiming that if someone were to enter anaphylaxis, nobody would have noticed? And the person would have been left, dying? That seems super unlikely. – Tim Nov 09 '21 at 19:53
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    @Tim: I was laid out on the asphalt unable to speak and nobody noticed. – Joshua Nov 09 '21 at 20:00
  • @carey in the U.K. 530,000 people die each year (out of 67 million). That’s 1 per minute, or 1.4e-8 per “man-minute”. In total, around 1 billion “man-minutes” have been spent waiting after the vaccine, so statistically one would expect around 15 (vaccine unrelated) deaths to have occurred across the U.K. during that 15 minute waiting period. – Tim Nov 09 '21 at 20:10
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    @joshua I’m sorry to hear that, I’m sure that was an unpleasant experience. However you appear to have survived? Did you recover without intervention, or did someone notice? – Tim Nov 09 '21 at 20:11
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    @Tim Yes, but the vast majority of those deaths would have occurred in a hospital or nursing home, not a vaccination center. And of those that did occur in a vaccination center, the vast majority of those would have been the usual reasons (heart attack and stroke), not anaphylaxis. – Carey Gregory Nov 09 '21 at 21:09
  • @CareyGregory well yes that was the point of my comment: do we have any data for non-anaphylaxis deaths? As Barmar mentioned. – Tim Nov 09 '21 at 21:10
  • @Tim: I received assistance from somebody who was not a healthcare worker. – Joshua Nov 09 '21 at 21:29
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    @Tim I would expect all deaths in the 15 minutes following vaccination would be reported to VAERS. – Carey Gregory Nov 09 '21 at 21:36
  • @RBarryYoung See my comments on other answer for other things to expect. The idea the only possible side effect from the vaccine is strictly anaphylaxis is... silly, for lack of a better word. It's the main, most serious (and still very rare), but it's not the only – TCooper Nov 09 '21 at 23:43
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For the UK up to 27 October 2021:

All recipients were requested to wait 15 minutes before departing the point of vaccination.

A history of anaphylactic reactions to any of the ingredients forbids taking the vaccine, but which dose (first or second) the listed reactions occurred after is not specified in the data.

Estimated first/second doses - Vaccine Manufacturer - Anaphylaxis or anaphylactoid reactions.

23.5/20.3 million doses - Pfizer/BioNTech vaccine - 517

24.9/24.1 million doses - AstraZeneca - 834

1.5/1.3 million doses - Moderna - 41

From UK Government website 8th November 2021.

With reference to the total number of reactions reported:

Pfizer/BioNTech - 357,084 (Anaphylactic data on page 31)

Astra Zenica - 836,957 (Anaphyl. data page 37)

Moderna - 55,081 (Anaphyl. data page 18)

A small number of reports from unspecified vaccines with 1 anaphylactoid reaction for 3,557 reports.

Jiminy Cricket.
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  • Sounds like this includes all allergic reactions, not just reactions detected during the 15 minute wait? – JonathanReez Nov 08 '21 at 23:42
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    I'm having second thoughts about the way data is differentiated in the UK. It's not clear at all from the figures that the 15 minute window is what's listed in that field (especially in light of the per-million figures for the US given by the other answers). @JonathanReez – Jiminy Cricket. Nov 09 '21 at 02:15