Still commonly shared online, the claim that we don't know the long-term side effects of Covid vaccines is untrue. In fact in the scientific and medical world, a year is considered 'long-term' when it comes to vaccine safety.
It is now (25th Feb. 2022) more than 14 months since the first Covid-19 vaccine dose was given, and a year since the first delivery of Covid-19 vaccines under the Covax scheme. Scientists explain that this is more than enough time for all but the rarest side effects to have emerged.
In fact the number of people who have received vaccine is more important than the length of time vaccines have been in use. New vaccines undergo stringent procedures to identify (a) whether it works, (b) if there are any side effects and (c) are the side effects mild or severe. In normal times, vaccine trials have gaps between the different stages due to researchers obtaining funding for the next stage. With Covid-19, funding was made instantly available, thus shortening the time from concept to production.
What happens in your body?
Covid vaccines may be new, but the processes they trigger in your body are not, and we know how the immune system works. Understanding how they stimulate the immune system can help us understand how quickly we can expect to have any negative reactions.
After 15 minutes
- A tiny fraction of people will have an allergic reaction to the inactive ingredients in the vaccine and this will happen within about 15 minutes of receiving it.
- Shortly after receiving the vaccine, the immune system recognises an alien invader and attacks it with immune cells, the weapons it would use against any virus or bacteria.
- In this innate phase, any reactions will happen within hours or a couple of days, including the most common side effects of a sore arm, temperature and other flu-like symptoms.
- Also in this phase is a much rarer side effect which has been linked to the mRNA vaccines Moderna and Pfizer is myocarditis (inflammation of the heart).
- While the exact cause of myocarditis is not understood, inflammation is one of the body's responses to infection or injury.
- Vaccine induced mycarditis is generally mild, and gets better on its own or with basic anti-inflammatory drugs such as ibuprofen.
- The innate phase also starts the second phase of your immune response - the adaptive phase - where your body starts to make cells which are specifically tailored to fight off the target virus.
- As this phase starts around 10 days after infection, which is why vaccines will take this length of time to begin to have an effect in protecting you against Covid.
- Your body pumps out new immune cells, peaking after about two weeks and fading away after about 28 days.
- A very rare but serious side effect linked to the Astra-Zeneca vaccine (a specific type of blood clot) happens during this phase and is related to the antibodies produced by your immune system in response to the vaccine. That is why most of these rare clots have been seen within four weeks of vaccination.
- Once the adaptive phase dies down - after about a month - you are left with memory cells which give you protection for months or years after initial exposure but don't generate new responses. If you have not a reaction after the first couple of months, it is incredibly unlikely that anything that happens after that will be caused by the vaccine.
- While there is never a 100% guarantee with anything in medicine, vaccination history shows that most side effects occur within hours of receiving the vaccine, and rare side effects within days or weeks.
Will we identify new side effects?
- From our hundreds of years of knowledge showing how the immune system works, an individual who has not had a reaction to a vaccine in the first couple of months, is vanishingly unlikely to have any new side effects after that.
- Countries world wide have put systems in place to monitor side effects and to share that information with each other.
- It is these systems that picked up both the blood clots and myocarditis, which are extremely rare with only a handful of cases per million doses.
- While milder symptoms (e.g. sore arm or temperature) are likely to be under-reported, the more severe side effects are thoroughly recorded.
- Billions of doses have already been given, so any side effect not yet seen would be rarer than one in a billion.
- While the vaccines have all completed the expected three phases of trials that usually take place before being offered to the general public, they are still being carefully monitored until at least 2023, to make sure even the rarest of events are identified.
All the evidence suggests that the overall risks of catching Covid far outweigh any risks from the vaccine.
