The Sputnik V vaccine Ad5 vector is evidently replication competent. The makers apparently neglected to delete E1, so getting this vaccine means being infected with live adenovirus 5.
Hence Brazil’s regulator correctly rejected it.
Adenovirus-vectored vaccines like J&J, AstraZeneca, and Sputnik V use infection with adenoviruses, common pathogens that usually cause common colds.
But to increase safety and decrease risk of side effects, most vaccine vectors delete the AdV E1 and E3 genes.
E1/E3 deletions are standard in Ad-vectors. Deleting E1 prevents the virus from replicating and deleting E3 prevents it from interacting with the immune system.
When making adenovirus-vectored vaccines, once you’ve deleted a region of the genome, it doesn’t just reappear out of nowhere. The presence of replicating virus suggests E1 was either not deleted or it recombined during manufacturing with a full length AdV genome.
This is disappointing. Ad-vectored vaccines are easier than mRNA vaccines to store and distribute, and are going to be important for vaccinating people in hard-to-reach places. Despite rare side effects, they are generally considered safe and trial data shows they are effective.
