Mix and match
The idea of mixing and matching vaccine doses – taking one type of vaccine for the first dose but switching to another manufacturer and technology for the second – is being explored by researchers as a way of opening up more doses to more people according to availability of each vaccine type.
There are studies under way on mixing and matching vaccine doses in such a way: but again the WHO says there is not yet enough data on this practice.
“There are people who are thinking about mixing and matching,” noted Dr Soumya Swaminathan, chief scientist, WHO at a press conference yesterday. “We receive a lot of queries from people who say they've taken one and they're planning to take another one. It's a little bit of a dangerous trend here where people are in a data-free, evidence-free zone as far as mix-and-match. There's limited data.
“There are studies going on; we need to wait for that. Maybe it will be a very good approach, but at the moment we only have data on the Oxford AstraZeneca vaccine followed by Pfizer.”
Israel – one of the most advanced countries in terms of initial 2-dose vaccinations – has said it will start offering a third dose of Pfizer to adults with weak immune systems. In the US, Pfizer has been talking to US officials on the possibility of authorizing booster shots.
But the WHO said it has not yet seen any indication there is a need for booster doses at this point.
Asked if the organization has seen any serious decline in vaccine efficacy after a six month time period – and specifically a decline that would require a booster shot – Dr Ann Lindstrand of the WHO responded: “We do not have… enough evidence that can point us to the need for booster doses. There is a decline, as there is with many different vaccines, but if you have a full course of vaccination of any of the WHO EUL [Emergency Use Listing] vaccines, you do have good protection.”
Furthermore, she emphasized the need to distribute such doses elsewhere where there is greater need.
“If you look at it on the global public health impact, at this point in time it’s more important to be able to vaccinate a larger global population with the vaccines we have: rather than expanding to use the limited supply of doses we have in giving them to already-vaccinated populations. So it’s very, very important now to rethink in those countries who have either started or are thinking about starting to use booster doses, that they do reconsider and think of it from a global perspective.
“SAGE, our strategic advisory group of experts, are definitely looking at any evidence coming through on the need booster doses, but at this point in time there’s not enough data for us to point up the importance of booster doses.”