COVID-19: Booster jab rollout ready from the autumn - but which vaccine to give?
Over-50s could be given a booster of the COVID-19 jab in the autumn to protect those most vulnerable from the virus.
With the vaccine rollout going so well and daily deaths dwindling to single figures, the challenge now is how to future-proof our shield against the virus - and prevent the need for another lockdown.
The Chief Medical Officer has been signalling since the start of the year that booster doses are likely to be given to the vulnerable in the autumn.
And Vaccines Minister Nadhim Zahawi told Sky News: "We want them to be able, if they need to, from September onwards to boost those that are most vulnerable".
That looks increasingly certain, probably for everyone over 50 - they are the most likely to suffer severe disease if their immunity against the virus wanes.
And once again the oldest are likely to be at the front of the queue, just as they were in the spring. Their immunity from a vaccine tends to be lower and less durable.
So, topping up the protection of the over-80s, perhaps along with their flu jab, makes complete sense.
They then stand the best chance of remaining fit and well through the winter months when respiratory viruses are more common.
The big decision for government scientists is which vaccine to give.
Is it just another dose of one of the existing vaccines? They give excellent protection against the original COVID-19 virus and the Kent variant.
They are also likely to prevent many - but probably not all - cases of severe disease caused by the South African and Brazilian variants of the virus, which have mutations that help them to evade the immune system.
So, the alternative strategy is to give a vaccine that has been tweaked to be more effective against the more threatening versions of the virus.
Moderna and Pfizer already have clinical trials of updated vaccines underway and other manufacturers are planning new formulations of their jabs.
But switching to protection against emerging virus has a peril - there is a danger of jumping too soon.
So far there have been fewer than 1,000 known cases caused by the South African and Brazilian variants in the UK - and keeping immunity topped up against the more common strains may be more important.
It's a tough decision. The virus will also keep evolving.
A virus that spreads and causes serious disease - a vaccine escape mutant - is a serious concern.
Public Health England's decision to expand the bio-secure testing facility at Porton Down makes sense, so new vaccines can be tested against emerging viruses.
It will give scientists and vaccine manufacturers an early warning of a problem.
Like flu, the COVID-19 virus will be around for years to come.
Keeping the vaccine as effective as possible could be the difference between freedom and lockdown.