Is the Pfizer Covid vaccine safe? How the coronavirus jab works - and mild side effects explained
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The first vaccinations against Covid-19 have started in Scotland, with health and social workers and residents in care homes the first to receive the jab.
The MHRA recently approved the vaccine for widespread rollout, and immunisations are being given to the most vulnerable citizens first.
After months of uncertainty caused by the pandemic, the world felt a glimmer of hope as Pfizer and German company BioNTech announced early results in November that showed their vaccine was more than 90 percent effective.
Excitement swept the world as it seemed like an end to the war against the virus was finally in sight.
The results came from a phase three clinical trial of the vaccine, which assessed how well it works in preventing people from becoming infected.
Ten million doses of the vaccine are scheduled to arrive in the UK before the end of the year, and a total of 40 million doses have been ordered which is enough to vaccinate 20 million people.
Here’s what we know so far about whether the vaccine is safe.
How does the vaccine work?
Pfizer and BioNTech’s vaccine is a new type called an RNA vaccine.
It trains the immune system to fight off coronavirus, using a small piece of the Covid-19 genetic code.
Once injected, human cells are triggered to make part of the virus known as the “spike proteins”.
The immune system recognises these proteins as foreign, producing antibodies to attack the virus and guard against infection.
The vaccine is given in two doses, with three weeks in between.
Results from the phase three trial indicate that the vaccine protects more than 90% of people from becoming infected by coronavirus.
Is the vaccine safe?
Currently, there are no RNA vaccines approved for human use, although people have been given them before in clinical trials for other diseases.
The MHRA has since warned people with a history of severe allergies not to receive the Pfizer/BioNtech vaccine.
That includes anyone that has experienced a reaction so severe that they have been prescribed an EpiPen adrenaline injection.
However, reactions to vaccines are not uncommon, and can happen with others like the annual flu jab.
Pfizer and BioNTech reported no serious safety concerns after testing the vaccine on 43,500 people. However, volunteers who received it did say they felt side effects similar to a “severe hangover”, according to a report.
Some volunteers said they could tell they had received the vaccine, and not a placebo, due to experiencing headaches and muscle aches.
Significantly, participants in the trial were from diverse backgrounds since research has shown black and ethnic minority groups are at greater risk from coronavirus.
Before the large number of people were injected, the companies ran smaller clinical trials in May which were used to detect any safety issues.
Four versions of the vaccine were tested, and the one that produced the fewest cases of mild and moderate side effects - such as fever and fatigue - was advanced to the next stage.
If there were dangerous side effects after taking the vaccine, these should have become apparent then.
However, there’s a possibility that rarer side effects may emerge as millions of people are given the vaccine.
Regulatory agencies around the globe will decide whether to approve the vaccine for public use.
We don’t yet know if the vaccine stops people from catching and spreading the virus, or if it just prevents illness, and it’s also not yet clear how protective the vaccine is in different age groups.
Where else has a vaccine?
Across the world, there are 10 other vaccines in the same late-stage trials, including Oxford University, and companies are feeling optimistic after Pfizer and BioNTech’s news.
One of the several vaccines in final-stage testing is developed by Chinese firm Sinovac Biotech.
Despite still undergoing trials in other countries, like Brazil, Indonesia and Turkey, the company has already been using their CoronaVac jab to immunise hundreds of thousands of volunteers in China under an emergency use programme.
There have been no reports of adverse reactions to the vaccine in China, although Brazillian president Jair Bolsonaro declared suspension of the trials in his country after a volunteer died.
However, the head of the Brazilian research centre coordinating the trial said the participant’s death was not related to the vaccine.