The UK currently has a surplus of vaccine, well beyond the amount we need to vaccinate our entire population. Any vaccines that are not required by the UK should be donated to poorer counties free of charge.
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Covid-19 is a global issue and as such we should be taking a global view of the treatment and prevention. Some countries do not have enough vaccine for their population: people there will die who could be saved. There will also be a huge reservoir of the virus giving it more chances to mutate as has happened with the Delta variant. Giving the extra vaccines away will help to prevent this.