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The vaccine trial phases
...the real race to a vaccine starts, with clinical tests on humans. It starts with Phase I, with a few dozen patients, in which you look for the best dose of the vaccine in humans, while observing minimal side effects. It is a safety phase. This Phase I takes various weeks, probably at least two months, because you first need to inject the vaccine to a small number of patients, and wait a week or longer to get results. Then you do the same with another few people, and with a higher dose, and again you wait, and so on, until you get to a target dose you will use for the Phase II and Phase III trials.
Then comes Phase II, with hundreds of patients, to prove the vaccine candidate creates anti-bodies and creates immunity response. This phase uses healthy people who are not necessarily faced with the virus, and it will also take a few months. You probably need to give multiple doses, particularly for the RNA, DNA, vector and recombinant vaccines, because they break down typically before creating strong immunity. You need a 3-4 week interval in between each 'boost', and see how the body reacts (that can take a week or two). So for this phase again you need at least two months, and more probably, three months.
Then comes Phase III, where you do a real test for effectiveness, and protective immunity: can the vaccine immunity protect against the infection for the disease? This is the 'make or break' phase that will determine whether we have an initial 'winner'. But the phase will take even longer, as you'll need to include a lot of people in your trial to know effectiveness: some will get the real vaccine, and others the placebo, and you need to follow them over time to know if there's a difference in infection between the two groups. That, of course, is a problem: many societies have either strict lockdown measures in place (in much of Europe, the Americas, and the Middle East). Or they have very few infections anymore (in China, Korea, Singapore, and other parts of East Asia).
Either way, this phase will easily last six months, and again, possibly (much) longer, and for the front-runners, will likely start in the fall of 2020. When it takes place, you can see two logical candidates for trial groups: people who live in homes for the elderly, where there are a lot of infections, and people who work in the health sector. The the second group is the most logical, because they are healthy and likely to get exposed to the virus. But you will have to make sure to choose those healthcare workers who haven't gotten the virus before.
