I had my first shot about 1.5 months ago, I just had my shot yesterday. Unmistakable fever like symptom started within 4 hours. within 10 hours the whole body started aching, accompanied with chill, tiredness and headache.

2 details in this chain of event I can't explain:
(I believe those 2 details are related, I just couldn't connect the dots)

base on the 2 conclusions I just accepted without truely understanding them:

  • fever is an innate immune system function
  • adaptive immune system kicks in after days

it is hard to explain the lack of fever after the first dose (maybe the body is just treating the first dose as a local wound with some oppotunist bacteria getting in). It is even harder to explain the extreme quick onset of fever after the second dose (maybe I have left over CD4 CD8 plasmaB cells in response to first shot still wondering around or not commit suicide yet in the body?)

muscle and joint pain should be due to white blood cells releasing cytokine. The vaccine's lipid particles are injected into my arm muscle, not major blood vessels. Those lipid particles couldn't travel far into my whole body, lipids alone do not last long. They should only merge with or "infect" mostly local cells around the injection site. local pain, local ache makes sense, why did the whole body's immune cells ALL decide to release cytokine? shouldn't the aching be a gradient though out the body? starting from the site of injection, it should hurt the most, gradually the pain will be lowered the further away from the site of injection.

the whole question is based on the knowledge that adaptive immune response takes days to take effect. I just assumed the 2nd shot's side effect which takes merely hours to manifest couldn't be the adaptive immune response. However, I am thinking now, maybe the side effect is the continuation of the adaptive immune response from the first shot?

apparently nanolipids don't just stay locally
body ache is immensely way more complicated

  • 5
    $\begingroup$ This is a personal medical question, so it may get rightfully closed. But I think the underlying biological question, and how you pose it, is excellent. I also think that the understanding we have on the mechanisms of immunogenicity of the COVID-19 vaccines is still limited; it takes time to study them to a level that would satisfy your answer. I hope you understand that. I think a question about why secondary/booster vaccine shots may sometimes induce worse side effects is a good one, perhaps you can try to do your own research on that, and ask here once more, if this question gets closed. $\endgroup$
    – S Pr
    May 14, 2021 at 8:07

1 Answer 1


To summarize the question, you are asking why:

  1. the first and second vaccine shot did not induce the same immune response in terms of fever.
  2. you experienced muscle and joint pain throughout your body even though the vaccine was injected into your arm muscle.

Regarding #1, your guess is mostly correct. According to Dr Melanie Swift, co-chair of the COVID-19 Vaccine Allocation and Distribution Work Group at Mayo Clinic:

When you take two doses of a COVID-19 vaccine, the first dose is the first time for your body to see the spike protein that the COVID-19 vaccines produce, and your body begins to develop an immune response. But that happens slowly. Then when you come back with a second dose, your body is ready to attack it. Your body is primed by that first dose of vaccine. The second vaccine dose goes into your body, starts to make that spike protein, and your antibodies jump on it and rev up your immune system response. [Source]

As for #2, I believe that the pain and soreness near the injection site is a separate symptom from the muscle and joint aches throughout the body.

The paper COVID-19 vaccine-related myositis has an explanation for the localized symptoms near the injection site:

With intramuscular vaccination, muscle is exposed to modified contaminant agents through direct inoculation, which elicit an immune response to the injected antigen. [...] Although similar to the COVID-19 infection itself the exact mechanism causing damage to the injected muscle is not known, it is worth reporting our observation of myositis suggesting a causal relationship to the novel, modified mRNA COVID-19 vaccine-adverse event, myalgia.

So, the arm symptoms seem to mostly be a localized reaction to modified contaminant agents which are injected.

As for the muscle and joint aches throughout the body, these are part of the general immune response which the body exhibits against the spike proteins which are eventually created. You are right that these symptoms are caused by cytokines, which are created by macrophages and neutrophils.

While it is true that the spike proteins will be manufactured by cells near the injection site, and will be detected there, this will trigger an immune response all throughout the body. This is similar to how a respiratory infection triggers an immune system throughout the body, and not just near the respiratory system.

As explained in an article on Breakthroughs.com, cytokines are chemical messengers which tell the body to produce more immune cells to help combat the infection. Their effects are intended to impact the whole body, which is why they cause symptoms on the level of the whole body, such as fever and muscle aches.

  • 1
    $\begingroup$ To summarize, "adaptive immune response takes days to take effect" is true, but that's the time it takes to adapt, not to react. Once the adaptation is done, it can respond immediately to the known antigen. The purpose of the vaccines is to eliminate that delay. $\endgroup$
    – timeskull
    Jan 25, 2022 at 15:29

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