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Many readers had questions about the newly formulated coronavirus vaccine, which is now available in most pharmacies and some doctor’s offices. As promised, this week’s newsletter is dedicated to answering them.

“How can one tell if the provider has the ‘new’ covid booster and not the leftover ‘old’ version?” asks Greg from Washington.

The best way is to call the pharmacy or doctor’s office ahead and ask. The new Pfizer and Moderna vaccines approved by the Food and Drug Administration target the KP.2 variant. Last year’s targeted XBB.1.5. It’s also prudent to double-check just before getting the shot to be sure.

Janet from Virginia wants to know about the Novavax coronavirus vaccine, which the FDA just approved. “How does this vaccine differ? Will it be available? Are there any reasons to wait for it?”

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The shot differs from Pfizer’s and Moderna’s in two key ways. First, it is protein-based, not mRNA-based like the other two. Second, it is formulated against the JN.1 strain, which is the predecessor of KP.2.

As far as I know, there are no head-to-head studies in the works comparing the effectiveness of the three vaccines. People who have reasons to avoid mRNA-based vaccines........

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