Covid-19 vaccines: All we know so far and the challenges ahead

Huge logistical task looms when drugs ready since double doses needed for most people

If vaccines stop 90% of infection, herd immunity is realisable. File photograph: Getty

If vaccines stop 90% of infection, herd immunity is realisable. File photograph: Getty

The northern hemisphere faces a bleak winter of rising Covid-19 cases, but signals that two rapidly engineered vaccines by Pfizer and Moderna work on 95 per cent of candidates on whom they have been tested have prompted joy.

The results are interim ones but they are, nevertheless, figures from large-scale Phase 3 clinical trials. The first 40 million doses could be administered in the United States by the year end.

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