What Vaccine Side Effects Can You Expect?

 


With more people getting vaccinated, and some people now getting their second dose, it seems like a good time to talk about likely side effects. The vaccine safety trials collected data that provide a basis for predicting what side effects are most likely.

Strangely, in my view, the trials did not measure the exact same side effects (though there was large overlap) and did not provide data on the same levels of reaction. For instance, Pfizer reported the percentage of cases that had any, mild, moderate, and severe reaction. Monderna, on the other hand, only reported percentages with any, severe, and requiring-hospitalization reactions.

Here is a comparison of the Moderna and Pfizer vaccines for percent of people experiencing any reaction (data cribbed form here):  
*Only measured in one study

The chances of any reaction are higher with the Pfizer vaccine, except muscle pain, joint, pain, and nausea or vomiting, which are higher for Moderna.  With either vaccine, you're going to get a sore arm.  When I got the first shot of Moderna, my arm was quite sore for three days.  Chances are about one out of three for fatigue and headaches and drop rapidly after that. 

Here are the percentages for severe reactions:

*Only measured in one study

Here Pfizer seems to have the edge in terms of fewer severe reactions. But thankfully the chances of any severe reaction are less than two in 100.  

Another thing to bear in mind is that the second shot is more likely to produce side effects, according to the CDC.  That's because the first shot primes your immune system to recognize and react to the virus and the second one kick-starts the reaction.

So remember that the side effects are evidence the vaccine is working.  Whatever the reactions are you can be sure they're better and shorter lived than a serious case of COVID-19.  Also remember that once we ramp-up vaccinations, we will start impacting the pandemic in a good way.

Update March 6

Swollen lymph nodes, a side effect noted in the charts above, have been causing problems with medical imaging used for cancer screening.  More in today's post.  


Image:  "Syringe and Vaccine" by NIAID is licensed under CC BY 2.0 

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