Doug Kerr
Well-known member
There has been considerable misexplantion today of a matter relating to the packaging of the Pfizer COVID-19 vaccine, a thing I had researched a couple of days ago from the formal documents prescribing vaccine handling (since I was curious as to how it was done). Here's the story.
The vaccine is distributed in "2 mL" glass vials. (That means they are intended to hold up to 2 mL of medication; the actual capacity "to the brim" is about 3.0 mL.) Each vial as shipped contains 0.2 mL of concentrated vaccine, frozen (to say the least).
Typically in the morning before beginning a vaccination session, the vials to be used are thawed, and 1.8 mL of 0.9% saline solution (AKA "normal saline") is injected into each vial (and yes, then 1.8 mL of air is drawn out to return the pressure inside to ambient). The vial now holds very nearly 2.0 mL of ready-to-use vaccine. (Very nearly? The two ingredients may not combine by volume exactly as we might think, so the quantity might be a little off that, even if the dilution is done precisely.)
The vial is prelabeled to indicate that it (after dilution) contains "five 0.3 mL doses". But that would ideally be a total of only 1.5 mL What about the other 0.5 mL? Well, seemingly, this was for "margin". For example, the person administering the injection might well draw a little more than 0.3 mL into the syringe and then shoot the excess into the air to get an exact load in the syringe. (Well, often in practice today, draw a lot extra . . .) And to do that, we by definition "waste" some of the content of the vial. And so the plan was likely to provide what might be a traditional amount of "margin" for this (and to deal with small errors in the dilution process).
Now some people had observed that with a reasonable amount of care, it should be possible to get six 0.3 mL doses out of a vial of diluted vaccine (and there is still some margin). And given that this vaccine is today so precious, maybe that would be a reasonable approach.
And I just heard on CNN, during one of the misexplanations of this, that the FDA has today said, in effect, "If you can get more than five doses out of a vial of properly-diluted vaccine, then do it."
Cool.
Best regards,
Doug
The vaccine is distributed in "2 mL" glass vials. (That means they are intended to hold up to 2 mL of medication; the actual capacity "to the brim" is about 3.0 mL.) Each vial as shipped contains 0.2 mL of concentrated vaccine, frozen (to say the least).
Typically in the morning before beginning a vaccination session, the vials to be used are thawed, and 1.8 mL of 0.9% saline solution (AKA "normal saline") is injected into each vial (and yes, then 1.8 mL of air is drawn out to return the pressure inside to ambient). The vial now holds very nearly 2.0 mL of ready-to-use vaccine. (Very nearly? The two ingredients may not combine by volume exactly as we might think, so the quantity might be a little off that, even if the dilution is done precisely.)
The vial is prelabeled to indicate that it (after dilution) contains "five 0.3 mL doses". But that would ideally be a total of only 1.5 mL What about the other 0.5 mL? Well, seemingly, this was for "margin". For example, the person administering the injection might well draw a little more than 0.3 mL into the syringe and then shoot the excess into the air to get an exact load in the syringe. (Well, often in practice today, draw a lot extra . . .) And to do that, we by definition "waste" some of the content of the vial. And so the plan was likely to provide what might be a traditional amount of "margin" for this (and to deal with small errors in the dilution process).
Now some people had observed that with a reasonable amount of care, it should be possible to get six 0.3 mL doses out of a vial of diluted vaccine (and there is still some margin). And given that this vaccine is today so precious, maybe that would be a reasonable approach.
And I just heard on CNN, during one of the misexplanations of this, that the FDA has today said, in effect, "If you can get more than five doses out of a vial of properly-diluted vaccine, then do it."
Cool.
Best regards,
Doug
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