Change in vaccine policy is a high-stakes gamble | Letters

The effectiveness of delaying the second dose of Covid vaccines must be carefully monitored, argues Dr Grizelda George, while Jan Mortimer and Jenny van Tinteren fear the move will increase distrust and uncertainty

The manufacturer of the Pfizer/BioNTech vaccine has said its efficacy has only been assessed for two doses given three weeks apart. Therefore the idea that a single dose will be protective beyond three weeks is speculative (Covid vaccine: chief medical officers defend rescheduling of second doses, 31 December). It would be truly tragic to vaccinate millions of recipients with the Pfizer/ BioNTech vaccine (at considerable effort and financial cost) with a twelve-week gap between doses if this doesn’t give them protection.

It is worth noting that there is likely to be a correlation between the antibody response and protection from infection. Therefore volunteers who have already completed two doses could be asked to give a small sample of blood to check the level of neutralising antibodies present four weeks from the first dose. Recipients whose second dose has been postponed after 4 January could give a similar sample from 11 January onwards to check their levels at the four-week point. A relatively small number of volunteers (perhaps 20 or 30 in each group) might settle this.

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