Higher exposure to spike protein seems to cause more health problems. Moderna has a higher dose of mRNA and likely causes the body to produce more spike protein than Pfizer and J&J.
Side effects are more common in women, more common after previous vaccination, and (!!) less common in older people.
Analysis of COVID-19 Vaccine Type and Adverse Effects Following Vaccination
The strongest factors associated with adverse effects were
- vaccine dose (2 doses of BNT162b2 or mRNA-1273 or 1 dose of JNJ-78436735 vs 1 dose of BNT162b2 or mRNA-1273; odds ratio [OR], 3.10; 95% CI, 2.89-3.34; P < .001)
- vaccine brand (mRNA-1273 vs BNT162b2, OR, 2.00; 95% CI, 1.86-2.15; P < .001; JNJ-78436735 vs BNT162b2: OR, 0.64; 95% CI, 0.52-0.79; P < .001)
- age (per 10 years: OR, 0.74; 95% CI, 0.72-0.76; P < .001)
- female sex (OR, 1.65; 95% CI, 1.53-1.78; P < .001)
- having had COVID-19 before vaccination (OR, 2.17; 95% CI, 1.77-2.66; P < .001).