Pfizer-BioNTech's updated booster shot generates a stronger immune response against the omicron subvariants BA.4 and BA.5 compared with the original Covid vaccine, the companies said in a release Friday.
Pfizer's original vaccine formula, which was first administered to older adults in December 2020, was designed to target the original coronavirus strain.
The updated booster shot is designed to target the original virus strain, as well as BA.4 and BA.5, in a single shot.
Two independent studies posted online late last month suggested that the updated shots do not offer better protection against the new omicron subvariants than the original vaccines do.
The new findings may hint that the updated booster is better than the original vaccine, but not by much, said John Moore, a professor of microbiology and immunology at Weill Cornell Medical College.