As we’ve discussed in various contexts over recent months, a big, big question is whether mRNA vaccines prevent COVID infection itself or the just illness that the virus causes. If the vaccine keeps you from getting a severe case of the disease or dying that is obviously a huge benefit. But the initial efficacy studies could not rule out one possibility: that vaccinated individuals were still getting infected and that the vaccine was pushing their cases into the asymptomatic category. That may not be a huge difference for individuals. But it’s all the difference in the world in terms of stopping the on-going spread of the disease through the population.
Now we have a study that seems to address this question directly.