Professor Karina Butler:

This is, again, a very important question because we want to know the most effective way to use our vaccines in the community. The vaccine is authorised for an interval of up to six days. The initial recommended schedule was 21 days. It is currently being used on a 28-day schedule. If we extend the interval, the potential benefit is that one gets some vaccine into more people. We have seen that in the UK, that has contributed significantly to the reduction in hospitalisation and its overall early effectiveness rate has been around 70%. What is the downside to doing that? The downside is that one is not getting the maximum protection and a situation might arise where there is a level of partial immunity that might favour the emergence of resistant mutants, particularly if one has got ones that need the highest level of immunity. It is about trying to balance those competing benefits and risks to see what is the best schedule. The question is also whether we need to think about it depending on what the overall supplies of the Pfizer vaccine might be and what the impact on the programme will be because, again, any stretching out of those intervals will necessarily lengthen the time to get everyone fully vaccinated but there may be a point that is reasonable that gives a benefit without compromise. It is an important question. Where do we get the data from? Most of the early studies involved looking at the efficacy of a single dose. It was done at that very short interval before a second dose was given with the exception of the UK because that was really the only place that went to the 12-week interval. They have updated on a monthly basis their effectiveness data. It was still rather short-term but a report should come out at the end of this month - it usually comes out at about the 22nd or 23rd day of the month - to see if there are any problems with extending that interval or if it is something that is safe and might be beneficial.

Again, it depends on the level of supplies and the overall need. We know that two doses of the vaccine give people the best protection and the best response.