It's an evolutionary arms race. We still have the staggering spread of the virus in the wild, let alone a well controlled one like might be had with more ideal

It's an evolutionary arms race. We still have the staggering spread of the virus in the wild, let alone a well controlled one like might be had with more ideal circumstances. (Circumstances of reasonable precautions, regular testing, and thoughtful actions that benefit the greater good.) The 'bivalent' boosters, as far as I understand (non-expert), combine a widely proven safe (likely billions of individuals who've had the treatment at this point) technology and version of the vaccine, which might no longer match the dominant wild strain of the virus, with a derivative of that same vaccine tuned to that current dominant strain of the virus. In order to be most effective that updated booster should be used while the variation it was designed to protect against is still in the wild.