Five companies selected are developing different vaccine types, which seems wise to hedge for failure of one. 

$MRNA: mRNA
$PFE ($BNTX): mRNA
$JNJ: non-replicating viral vector
$AZN (Oxford): non-replicating viral vector
$MRK (IAVI, Themis): replicating viral vector https://t.co/TWuR9xYK3X