Of course they are dumping shares, I would do the same... The valuation of these vaccine companies is just crazy since the field will get more and more crowded next year - Novavax, J&J and Sanofi will enter too... The revenues and profits will go down steadily after 2 years and don't justify a 60b valuation in Moderna's case - nothing else close to commercialisation to justify such a lofty market cap ... There is just no reasonable upside left in these stocks.
If you conclude they don't work from insider sales, you'd need to worry with CYDY insiders having sold shares too, particularly Welch.
The mRNA technology is spectacular and it is a major breakthrough in the field. The data could have hardly been any better.