If you have a choice pfizer booster seems better than Moderna - lots of folk including me have an unpleasant 24hrs or so after that moderna booster - very achey arm.
I can second this - had very minor side effects after my original two doses of AZ but had my Moderna booster on Friday afternoon (walk in, under 40, just over 5 months since second dose) and felt absolutely terrible yesterday. Fever, chills, nausea, terrible headache, muscle aches, light sensitivity, eyes hurting, dizzy, v painful arm, pretty much every side effect there is. Feeling much better today but still not 100% back to normal. I’d definitely recommend making sure you have a day off to recover after the booster.
However, even after experiencing this first hand I don’t think the side effects are enough of a negative to avoid Moderna in favour of Pfizer If you have the choice. The evidence suggests that Moderna is slightly more effective than Pfizer, at least against Delta.
Compared with the Pfizer COVID-19 vaccine, the Moderna COVID-19 vaccine has a slightly lower risk of COVID-19 outcomes, including hospitalization and death.
www.hsph.harvard.edu
This report describes COVID-19 vaccine effectiveness against hospitalizations for all three vaccines, with Moderna as the most effective against hospitalization.
www.cdc.gov
Both of the mRNA vaccines available in the US are highly effective against severe COVID-19, but recent studies suggest that Moderna’s elicits a stronger immune response and might be better at preventing breakthrough infections.
www.the-scientist.com
A full dose of Pfizer has 30mg of the active mRNA ingredient compared to 100mg in a full dose of Moderna. The Moderna boosters are half doses, so 50mg of active ingredient, which is still higher than the full dose Pfizer booster and may explain why the side effects can be worse. Personally I’m happy to go through more unpleasant side effects if there’s even a chance of slightly higher protection.
Anecdotally, everyone I know in healthcare recommended Moderna over Pfizer if I had a choice between the two, but if not to go with whichever I could get soonest.