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COVID-19 Vaccine 101: Your Top 4 Questions Answered

We worked with doctors and nurses to help answer popular questions about COVID-19 vaccines. Learn about the side effects, variants and different efficacy rates.

A special update from our epidemiology and clinical teams:

We have rounded up our board of clinicians and epidemiologists to brief you on what to expect when you get your vaccine.

We asked hundreds of Kinsa users who already received their immunization “What do you wish you had known before getting your vaccine?” In response, our docs and nurses answered these following burning questions:

  • Of the J&J, Moderna and Pfizer vaccines, is one better than the other two? Can I choose which vaccine I get when I’m eligible?
  • What side effects might I experience as a result of the vaccine? How long should I expect those side effects to last?
  • Are new variants of the virus going to mess with our efforts to end the pandemic with the vaccine?
  • How long after my vaccine will immunity kick in?

Before we dive in, a caveat: there is a lot of information - and thus, unfortunately, misinformation - circulating about the vaccines right now. Tread lightly when reading top search results - those are often at the top because they rank as the most-clicked articles, not because they’re from the most reputable sources. Here, we’ve compared our answers against the CDC, WHO and renowned medical centers like the Mayo and Cleveland Clinics. Phew. With that said, let’s dive in.

Is one vaccine better than the others?

Don’t split hairs over which vaccine you get. They’re all phenomenally effective. Because vaccine supplies are so limited, you likely won’t have a choice between the three - the one available at your vaccine provider is the one you’ll get.

If you’ve heard whispers of the J&J vaccine “only” being 66% effective versus the Pfizer and Moderna vaccines being ~95% effective, know that this isn’t the whole story. All three vaccines are 100% effective at preventing people from getting hospitalized and from dying.

If you want to get really technical, the 66% effectiveness from the J&J vaccine refers to its ability to prevent moderate COVID-19 symptoms. This means that while in some cases the vaccine may not totally prevent disease, it can make symptoms more mild and manageable if you do get sick. Plus, the J&J vaccine was tested in a few countries where different variants were spreading, while Moderna and Pfizer’s were only tested in the US before different variants were circulating. Thus, the J&J vaccine likely had a harder test to pass when it came to measuring effectiveness than the other two.

The bottom line: all three vaccines are safe and highly effective. The risk you accrue by waiting to get your vaccine of choice outstrips any small differences in protection the different vaccines confer.

Will I experience any side effects from the vaccine?

Potentially some mild ones. If you end up getting one of the two-dose (Moderna or Pfizer) vaccines, know that you’re more likely to notice side effects after the second shot. This is totally normal! The fact that your body is mounting a protective response to the small bit of mRNA in the second shot means that the first shot worked - it primed your immune system to recognize and react.

Here’s how you can treat some of the most common side effects:

  • Sore arm at the injection site: non-intuitively, exercise it or move it around! Ice or a cool, wet towel can also soothe.
  • Fever: you may experience a mild to moderate fever 1-3 days after receiving your vaccine. If you need to take medication *after receiving the vaccine and developing a fever*, try Tylenol.
  • Headache: hydrate and again, if you need to take medication, take Tylenol.
  • Fever-associated symptoms like muscle aches and fatigue: hydrate, rest and treat yourself to a warm bath with epsom salt.

Pro-tip: avoid taking over the counter painkillers like Tylenol and Motrin in preparation for your vaccine, unless you already take them on a regular basis for a diagnosed medical condition. There’s been some research that suggests that they might dampen your body’s desired immune response.

Side effects that concerned our older users, but are also totally normal:

  • Swollen lymph nodes: if you feel hard, tender round lumps in your neck, under your chin, in your armpits or around your groin within a week of getting your vaccine, say hello to your lymph nodes. Clusters of immune cells live inside these guys, so the fact that they’re reacting to the vaccine by swelling slightly is also promising! We get it, mystery lumps in the body = terrifying. Know they’ll resolve with time. In the meantime, dip a towel in hot water, wait for it to cool and gently press it against any swollen lymph nodes you notice.
  • A rash that appears around your injection site a full week after your immunization (“COVID arm”): while most side effects appear within 1-3 days of receiving your vaccine, this big itchy, red blotch can be a jarring one that appears a week after your shot. Similarly to treating day-of injection pain, hold a cool, wet compress against the rash or try ice. The rash should subside within a few days.


What effects do different variants of the virus have on vaccine effectiveness?

Potentially some (vague, we know), but not enough to prevent existing vaccines from providing massive protection against predominating variants.

Humor us a nerdy epidemiologist moment. Seasonal flu is a direct descendant (a.k.a. “variant”) of the 1918 Spanish Flu - as in, the deadliest global pandemic since the Bubonic Plague. Variants are nothing new for viruses, they’ve just never commanded this type of media attention before. The same way having different variants of seasonal flu doesn’t make us hesitate to get the flu vaccine, having different variants of the novel coronavirus shouldn’t make you hesitate to get the COVID-19 vaccine.

How long do I need to wait after my vaccine for maximum immunity to kick in?

28 days after the J&J shot and two weeks after your second shot for both Moderna and Pfizer.

Once you clear the two week threshold, you are fully vaccinated and restrictions loosen a bit for you, with a caveat. The CDC is asking that if you live in an area where COVID-19 transmission is "high" or "substantial," you should continue wearing a mask indoors. As we approach school in the fall, students and staff should plan on wearing a mask during the school day as we did last year. If you're unsure whether or not your county falls into these guidelines, you can check here.


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