The national rollout of the AstraZeneca vaccine has started. COVID-19 was first identified only 15 months ago - since then the miracle development of a safe and effective vaccine is a real gift to the world. Some people are understandably a little concerned about the temporary pausing of this particular vaccine in Europe. As it rolls out across Australia, many are wondering if it's safe. Here's why we can be sure that it is. When new drugs and vaccines are developed, they are tested in four phases. The first three stages are careful clinical trials, which are designed to make sure the vaccine works, and is safe, in "healthy volunteers" - that is, young and fit people. Phase four is about seeing what happens with this vaccine in the general population - including older people with health issues. In the northern hemisphere there were a few people who had blood clots soon after having the vaccine, so the rollout was temporarily paused. This is a totally normal part of phase four monitoring. Specific information was collected about people who had and hadn't been vaccinated, including about blood clots. A thorough analysis showed that there were no more blood clots in those people who had been vaccinated compared with people who hadn't - in fact there were possibly slightly less. Therefore, the blood clots would probably have occurred even if they hadn't been vaccinated. Worldwide, the COVID vaccines have now been given to people for about three months - about 120 days. There are roughly two million doses every given each day and well in excess of 300 million doses so far all over the world. So, by now it would be very clear if there were problems. All that might happen are the usual things that sometimes occur after a vaccination (possibly a sore arm, slight fever, headache and so on). Which, of course, is far better than getting COVID. Now that winter is not so far away, it is also time for our annual flu shots. This year, we will be getting three immunisation shots - two COVID-19 about 12 weeks apart, and a flu shot somewhere in the middle. This might sound a little complicated, but it will all make sense when the time comes. So don't fear the COVID and flu vaccines - they will free us from worry. Dr Priscilla Robinson is an adjunct associate professor in the School of Public Health at La Trobe University.