By Michelle Roberts<\/strong> More than 60% of the world’s population – 4.8 billion people – have received at least one dose of coronavirus vaccine. <\/b><\/p>\n<\/div>\n<\/div>\n There are different approved types and brands available and all have undergone rigorous testing and safety checks. <\/p>\n<\/div>\n<\/div>\n Safety trials begin in the lab, with tests and research on cells and animals, before moving on to human studies. <\/p>\n<\/div>\n<\/div>\n The principle is to start small and only move to the next stage of testing if there are no outstanding safety concerns.<\/p>\n<\/div>\n<\/div>\n If the safety data from the labs is good, scientists can check the vaccine or treatment is effective. <\/p>\n<\/div>\n<\/div>\n That means tests on large numbers of volunteers – about 40,000 in the case of Pfizer-BioNTech, the first to be approved in the UK<\/a>.<\/p>\n<\/div>\n<\/div>\n Half are given the vaccine and the other half a placebo jab. The researchers and participants are not told which group is which, until after the results, to avoid bias.<\/p>\n<\/div>\n<\/div>\n BBC’s Laura Foster explains the order in which the Covid vaccine will be given<\/p>\n<\/figcaption><\/figure>\n<\/div>\n All of the work and findings are checked and verified independently. <\/p>\n<\/div>\n<\/div>\n The Covid vaccine trials happened at breakneck speed, but they didn’t skip any steps – they were able to move faster because so many people were involved and other projects were put aside. <\/p>\n<\/div>\n<\/div>\n Approval is only given if regulators are happy that a vaccine is safe and effective. <\/p>\n<\/div>\n<\/div>\n Checks continue after approval to make sure there are no further side effects or long-term risks. <\/p>\n<\/div>\n<\/div>\n In the UK, independent experts on the Joint Committee on Vaccination and Immunisation decide how best to use a vaccine and who should get it after approval by the Medicines and Healthcare Products Regulatory Agency.<\/p>\n<\/div>\n<\/div>\n Scientists hope to tweak coronavirus vaccines to ensure they continue to offer high protection as new variants of the disease emerge.<\/p>\n<\/div>\n<\/div>\n The UK’s drug regulator says new vaccines can be fast-tracked for approval<\/a> if needed.<\/p>\n<\/div>\n<\/div>\n No corners will be cut, with safety paramount. <\/p>\n<\/div>\n<\/div>\n But lengthy clinical trials with thousands of volunteers will not be needed.<\/p>\n<\/div>\n<\/div>\n Instead, data from existing studies and ongoing real-world use could be used.<\/p>\n<\/div>\n<\/div>\n Pfizer-BioNTech’s vaccine (and Moderna’s) uses bits of genetic code to cause an immune response. These are called mRNA vaccines. <\/p>\n<\/div>\n<\/div>\n They do not alter human cells, but merely present the body with instructions to build immunity to Covid.<\/p>\n<\/div>\n<\/div>\n The Oxford-AstraZeneca vaccine uses a harmless virus altered to look a lot more like the pandemic virus.<\/p>\n<\/div>\n<\/div>\n Vaccines sometimes contain other ingredients, like aluminium, that make the vaccine stable or more effective.<\/p>\n<\/div>\n<\/div>\n Vaccines do not give you a disease. Instead, they teach your body’s immune system to recognise and fight the infection they have been designed to protect against.<\/p>\n<\/div>\n<\/div>\n Some people do experience mild to moderate symptoms after being vaccinated. This is not the disease itself, but the body’s response to the vaccine.<\/p>\n<\/div>\n<\/div>\n Common reactions<\/a> that may affect more than one in 10 people and typically get better within days include chills, tiredness and aching muscles.<\/p>\n<\/div>\n<\/div>\n It is rare to find that health problems occurring following a vaccine are actually caused by the vaccine itself. Events may be coincidental and unrelated to vaccination. <\/p>\n<\/div>\n<\/div>\n The Oxford-AstraZeneca vaccine has been linked to very rare cases of blood clots<\/a>. This is not proof that the vaccine is to blame. Covid infection itself can also make clots more likely and they can occur naturally too. <\/p>\n<\/div>\n<\/div>\n The chance of this happening to an individual is still extremely low, but as a precaution, younger age groups in the UK have been offered alternative Covid vaccines.<\/p>\n<\/div>\n<\/div>\n Allergic reactions to vaccines are rare. For any approved vaccine, the ingredients are listed.<\/a><\/p>\n<\/div>\n<\/div>\n There have been serious but treatable allergic reactions in a very small number of people given the Pfizer-BioNTech vaccine.<\/p>\n<\/div>\n<\/div>\n As a precaution, the MHRA says people with a history of significant allergic reactions to any of the ingredients in this vaccine should not currently have this jab. <\/p>\n<\/div>\n<\/div>\n Be aware that anti-vaccine stories are spread online through social media. These posts are not based on scientific advice (or blend facts with misinformation). <\/p>\n<\/div>\n<\/div>\n
Health editor, BBC News online<\/span><\/p>\n<\/header>\n![\"Doctor](\"https:\/\/ichef.bbci.co.uk\/news\/976\/cpsprodpb\/2280\/production\/_115623880_yellow.jpg\")
<\/span>Image source, <\/span>Getty Images<\/span><\/div>\n<\/figure>\n<\/div>\nHow do we know a vaccine is safe?<\/span><\/h2>\n<\/p>\n
What role do trials have?<\/span><\/h2>\n<\/p>\n
Who approves vaccines or treatments?<\/span><\/h2>\n<\/p>\n
What is the fast-track approval for vaccines against new variants?<\/span><\/h2>\n<\/p>\n
What’s in the Covid vaccines?<\/span><\/h2>\n<\/p>\n
Will the vaccine give me side effects?<\/span><\/h2>\n<\/p>\n
What about serious reactions?<\/span><\/h2>\n<\/p>\n
What about allergies?<\/span><\/h2>\n<\/p>\n
![\"How](\"https:\/\/ichef.bbci.co.uk\/news\/1024\/cpsprodpb\/1453\/production\/_116730250_vaccines_comparedincl_janssen_novavax_29_jan_640_2x-nc.png\")