The Centers for Disease Control and Prevention recommends that everyone over 12 receive a “bivalent” Covid-19 vaccine as a booster dose. But only a select group are likely to benefit, and the evidence to date doesn’t support the view that a bivalent vaccine containing omicron or its subvariants is better than the monovalent vaccine. The existing Pfizer and Moderna mRNA vaccines were designed to protect against the original strain of the novel coronavirus, known as Wuhan-1. Between January 2020 and December 2021, D614G was replaced by the alpha variant then the delta variant. At the end of 2021, Oxford conducted a study to determine whether the mRNA vaccines still provided protection against severe illness and death caused by the variants.

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