Lots of people are getting covid boosters now. To help myself and others plan I did an extremely informal poll on Twitter and Facebook about how people’s booster side effects compared to their second dose. Take home message: boosters are typically easier than second shots, but they’re bad often enough you should have a plan for that.

The poll was a mess for a number of reasons, including:

• I didn’t describe the options very well, so it’s 2/3 freeform responses I collapsed into a few categories.
• There was a tremendous variation in what combination of shots people got.
• It’s self-reported. I have unusually data-minded friends which minimizes the typical problem of extreme responses getting disproportionate attention, but it doesn’t eliminate it, and self-report data has other issues.
• I only sampled people who follow me on social media, who are predominantly <45 years old, reasonably healthy, reasonably high income, and mostly working desk jobs. 
• I specified mRNA but not the manufacturer; Moderna but not Pfizer boosters are smaller than the original dose.

Nonetheless, the trend was pretty clear.

Of people who received three mRNA shots from the same manufacturer, comparing their second shot to their third:

• 12 had no major symptoms either time (where major is defined as “affected what you could do in your day.” It specifically does not include arm soreness, including soreness that limited range of motion)
• 2 had no major symptoms for their second shot but had major for their third
  • Not included in data: one person who got pregnant between their second and third shot
• 23 had major symptoms for their second shot, and the third was easier
  • This includes at least one case where the third was still extremely bad and 2-3 “still pretty bad, just not as bad as the second”
  • Three cases fell short of  “major symptoms” for the second, but had an even easier third shot
• 11 people had similar major symptoms both times
• 2 had major symptoms for second shot, and third was worse

Of people who mix and matched doses

• 2 had no major symptoms either time
• 4 had no major symptoms for their second shot but had major symptoms for their third
  • Not included: 1 reported no symptoms for the first two and mild symptoms for the third
• 4 had major symptoms for their second shot, and their third was easier
• 2 people had major symptoms both times
• 1 had major symptoms for their second shot, and their third was worse