Inflammation? Fever? What to expect after your second COVID-19 vaccine shot

A doctor answers your common questions on side effects and fatigue

By Nicole Karlis

Senior Writer

Published April 5, 2021 10:00AM (EDT)

A healthcare worker receives a dose of Pfizer-BioNTech Covid-19 vaccine (Wong Fok Loy/SOPA Images/LightRocket via Getty Images)
A healthcare worker receives a dose of Pfizer-BioNTech Covid-19 vaccine (Wong Fok Loy/SOPA Images/LightRocket via Getty Images)

Every day, millions of people in the United States are getting the COVID-19 vaccine. And as more shots end up in more arms, more questions arise—especially for the two-shot vaccines, which are still the majority of the vaccines distributed in the United States.

Anecdotally, many of the vaccinated report fatigue or even faint fevers after receiving their second shot. Podcaster Ellie Schnitt said she felt like she was "on her death bed" after her second shot. Producer and TV writer Scott Derrickson said he felt "like he had Covid" after his second dose.

Indeed, while it is certainly possible to experience side effects after dose one, there's a higher frequency of side effects after the second dose, according to clinical trial data for both vaccines

The vaccines that require two shots are the two from Pfizer and Moderna, which are both approved in the United States and are both made using messenger RNA, or mRNA. This mRNA technology delivers the genetic code of one of the virus's proteins to one's cells. The immune system learns recognize the spike protein on the SARS-2 coronavirus and develop antibodies to fight it. While both vaccines use the same technology, there are a few differences between the two.

First, the Pfizer vaccine has been authorized for people aged 16 and older; Moderna has been approved for people 18 and older. However, both companies are conducting vaccine trials for those in lower age groups. Second, both vaccines have remarkable efficacy; Pfizer is at 95 percent, and Moderna was 94.1% effective at preventing symptomatic COVID-19 cases. Another major difference is the time between receiving the first and second dose— the second Moderna dose is 28 days. For the Pfizer vaccine, it's 21 days. This is partly because Moderna administers a larger first dose— 100 micrograms. The Pfizer dose contains 30 micrograms of the vaccine.

Salon interviewed Dr. Amesh Adalja, a Senior Scholar at the Johns Hopkins Center for Health Security, to answer some of readers' most pressing questions on how to prepare for one's second shot, and what to expect. As always, this interview has been condensed and edited for clarity. 

Should people take time off of work for a day or two, or let their bosses know that they'll be getting the second dose, in case they're not feeling well?

I wouldn't necessarily preemptively take a day off, but I would probably let people know that you're getting a vaccine and just to be a little more understanding and maybe flexible about that, because it's unpredictable. I know people who have had a second dose and had no problems at all. I myself had a second dose and went and worked an overnight shift in the ICU afterwards. I felt a little achy, but it was fine. And then there are other people who have more severe symptoms, so I think it really is variable. I would just let people know that that's what's happening. And have some flexibility built into that.

Fatigue is a common side effect. For the Moderna vaccine, the highest rate of fatigue reported were by trial participants 18 to 64 years after the 2nd dose. More than half of Pfizer trial participants reported fatigue after the second dose, too. But people are wondering, how much fatigue should they expect to experience? Is it possible that too much fatigue would be alarming, and someone should call their doctor if they're experiencing it?

Some people spend the day in bed, and other people feel tired but they still go about their day. I think it's variable.

It's usually just you feel tired, you feel more sleepy than normal, that's basically how most people experience it. It's hard to know exactly how much the fatigue is concerning because it's such a subjective type of complaint, and also depends on your baseline and other medical conditions that you may have. I would say for the 36 or so hours post-vaccine that it's probably normal to feel fatigue after that. If it continues then I think it may be something else unrelated to the vaccine, or something you might need to be formally evaluated for.  I don't think there's any hard and fast rule to come up with, because you have to kind of look at each person's baseline and understand where they fit.

Are there any side effects people should keep their eye on after the 15 minute observation period is over?

The 15 minutes period is meant to screen out people that might have severe allergic reactions. Severe allergic reactions are unlikely to occur after that period of time. You may still have the aches and pains. Some people with the Moderna vaccine get a rash several days later at the injection site. Some people do get those Moderna rashes evaluated by their doctors, but it's not something that requires you to call 911.

People have asked if they can take over the counter medicine after they received the vaccine — say, Ibuprofen and Advil. What are your thoughts on that?

I took acetaminophen (which is Tylenol) about 12 hours, or maybe 18 hours, after the second dose because of a headache, some muscle aches and pains. I think it's completely fine to do that.

There are some theoretical concerns about using  non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, naproxen, which brand names are Advil or Motrin or Aleve, because they think it might blunt the immune response. There have been some studies with other vaccines, but I don't know if it's clinically significant. But for people that have that concern, you could take acetaminophen, or Tylenol — it's not an anti-inflammatory drug.

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What about drinking alcohol? There have been some reports of people in other countries being advised not to drink after receiving the vaccine.

I don't think it makes a big clinical difference. The only thing I would say is just be careful with alcohol and then blaming the vaccine for your hangover. You know, or if you get nausea and vomiting or you get a headache because you're hung over.

Another side effect is swollen lymph nodes.

That's not necessarily just a second dose side effect, that can happen anytime. A lot of these things could happen with either, but yeah, you can get swollen lymph nodes. After a vaccination, that's not uncommon. It happens with other vaccines as well.

That's one of the sites of your immune system, where it's housed, so it's not uncommon to see that increased activity of your immune system be correlated with increased lymph node swelling, which is usually transient and goes away just like when you get swollen lymph nodes after a sore throat, for example.

When the lymph node swells, the one that swells is closest to where the site of inflammation is in the site of inflammation. The site of inflammation with this vaccine is your deltoid muscle, which is going to drain to your axillary lymph node, so the lymph nodes in your armpits. So those are the ones that you wouldn't you'd maybe see get full in versus the ones in your neck which you get sometimes after, you know, what, when you have strep throat.

Some people have wondered, "if I'm not having any side effects is the vaccine working?"

You can't make that kind of a claim. In general, when you do have those side effects it is the result of your immune system but the absence of those side effects doesn't mean that you're not getting a take, or we call say "the vaccine is not taking." We can't really say that some people have no symptoms at all with the vaccine and they have a perfectly appropriate response to it, immunologically.

Do either the Moderna or Pfizer vaccine have more side effects than the other?

These weren't studied in head to head trials, so it's very hard to make comparisons.

By Nicole Karlis

Nicole Karlis is a senior writer at Salon, specializing in health and science. Tweet her @nicolekarlis.

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Covid-19 Vaccine Moderna Vaccine Pfizer Vaccine Reporting Vaccine Side Effects