There are a number of vaccines in development and the UK Government have agreed deals for 340million doses of vaccine from 6 companies. There is no certainty that a particular vaccine will succeed so the government is investing in a number of different ones in order to maximise the chances of finding a successful and effective vaccine.
There are 9 vaccines in the final stages of development currently undergoing final stage 3 trails. Here the vaccines are tested on thousands of volunteers. Volunteers are divided into two groups, half of which receive the vaccine and half receive a placebo. The effectiveness of the vaccine is measured by comparing the numbers in each group who become infected.
The vaccine being developed in the UK by AstraZeneca and Oxford University recently stated that they were hopeful of being able to start distribution of their vaccine shortly. Pfizer in the US in conjunction with a German company BNioNtech are at a similar stage, although both consortia are using different technologies. Each will require 2 doses for effective immunity.