Unlike most other common vaccines, like flu or measles, where the full content of a vial is injected into a person’s arm, each bottle of Covid vaccine contains multiple doses of the serum.
A vial of the Pfizer-BioNtech vaccine, which has been in use in Switzerland since December 23rd, contains up to six 0.3-millilitre (ml) doses per bottle.
However, Switzerland’s regulatory body, Swissmedic, says special precision syringes would be needed to extract six full doses from each vial. As standard syringes are used, only five doses can be used.
“At the end of the day there are leftover doses in each vial”, Ticino’s cantonal pharmacist Giovan Maria Zanini said in an interview with Corriere del Ticino newspaper.
But the serum remaining in each vial is basically wasted.
“If there were only 0.2 ml left in the bottle and it would be injected, the necessary protection from coronavirus can no longer be guaranteed”, Zanini said.
In other words, for the vaccine to be effective, a full 0.3ml dose has to be injected. And for the Pfizer vaccine recipients need two 0.3ml doses several weeks apart.
Vials must be discarded when there is not enough vaccine to obtain a complete dose.
This brings up a question of why the more precise syringes are not routinely used.
That's because there is not enough of them to go around, Zanini said.
“In Europe alone, with its half a billion inhabitants, if 75 percent of the population were vaccinated, 700 million syringes would be needed for two doses. We already have a problem finding standard syringes, let alone if we had to get special ones”.
Can the leftover serums be extracted from several bottles and mixed to obtain the sixth dose?
The answer is no. Residual vaccine from multiple vials can’t be combined to obtain a dose.
“Filling a syringe from different bottles is risky from the microbiological point of view”, Zanini said.
The Moderna vaccine, which was approved in Switzerland on January 12th but has not yet been used, manufactures vials containing 10 doses; 0.5 ml must be injected.
Both types of the vaccine share the same challenge, not only related to repartitioning each vial, but also making sure that, once opened, the highly perishable vaccine can be used quickly to minimise loss.
Switzerland purchased 13 million doses from three manufacturers: Moderna (4.5 million doses), AstraZeneca (5.3 million) and Pfizer (3 million ).
That is enough to vaccinate 6 million people out of Switzerland’s total population of 8.5 million, as each vaccine has to be given in two doses.