I don’t know about “strength”, to me that implies dosage size and/or concentration.
I understand Phizer included just 2% of the covid virus, while Moderna included either 19%. Moderna had more side effects, but didn’t wane as quickly as Phizer.
In March 2021 I had the J&J - thinking it was a traditional vaccine. Stupid me. At least I’m not a statistic...so far.