Within a year of COVID-19 appearing in the UK, the seemingly unthinkable has happened: vaccines for it have started being administered to people across the country.


The first of the coronavirus vaccines, the Pfizer vaccine, was approved by the Medicines and Healthcare products Regulatory Agency (MHRA) as safe to use on 2 December 2020. This assessment was made, according to the MHRA’s chief executive Dr June Raine, after “a rigorous scientific assessment of all the available evidence of quality, safety and effectiveness.”

For some people, however, the news was too good to be true. A YouGov survey indicated that one in five British people (and 42 per cent of those aged between 25-49) say they’re unlikely to take the vaccine. The majority of those surveyed cite safety concerns as the reason for their reluctance.

Could the coronavirus vaccine have hidden long-term effects?

With all coronavirus vaccines having been trialled for less than a year at this point, it’s true that their long-term effects are not completely understood. Yet scientists say it’s unfair to compare the vaccines to the likes of thalidomide.

First sold in the UK in 1958, thalidomide – a drug marketed as a sedative and treatment for morning sickness – was found to cause major birth defects when taken by pregnant women, three years after it appeared on the market.

First, unlike thalidomide, coronavirus vaccines are being tested with special consideration for pregnant women. For instance, while approved for most of the UK population on 2 December 2020, the Pfizer vaccine wasn’t given the green light for expectant mothers or those who are breastfeeding. This, the MHRA says, is now simply a “standard measure” for new vaccines that haven’t been specifically tested on that group.

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Experts also say long-term side effects for the general population are extremely low. “You would typically see the adverse effect of vaccines within the first couple of months. But many vaccines have been tested since June 2020 and we’ve seen no evidence of this so far,” says Dr Jeremy Rossman, lecturer in virology at the University of Kent.

“Is there a chance that there’s going to be some sort of effect that we’ll see months or two years down the line? Sure. It’s possible. But it would probably only impact an extraordinarily low number of people.”

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Rossman instead points to the higher risk of developing so-called ‘long COVID’. Using data from the COVID-19 symptom tracker app, it’s estimated between 1 and 10 per cent of people can still suffer from symptoms 10 to 12 weeks after their infection.

“And in many cases, people have symptoms that can last six months or more,” Rossman says. “We still don’t really understand long COVID and how dangerous it is.”

Why does the vaccine have to be injected?

While some current vaccines are administered through a nasal spray, coronavirus vaccines will initially be given through an injection in the arm. According to Rossman, this is simply because such vaccines are faster to develop, test and manufacture.

Future coronavirus vaccines could be delivered through the nose, however. In fact, institutions such as Imperial College London have begun trials to assess the safety and effectiveness of several vaccines, including the Oxford/AstraZeneca one, via a nasal spray. And many scientists predict this could prove even more effective than an injection.

“There are certainly good arguments for delivering a vaccine’s payload directly to the upper respiratory tract, like modern flu vaccines,” says Dr David Matthews, a virologist from the University of Bristol.

“[A vaccine delivery via the nose] will raise an immune response at what’s called the mucosal surfaces – the surfaces of the nose, mouth and the back of the throat. That’s where you really want a strong and effective immune response if you’re going to beat off a respiratory virus. And, crucially, a nasal spray is going to require less training to administer.”

The UK’s programme of COVID-19 vaccinations began in December 2020 © Getty Images
The UK’s programme of COVID-19 vaccinations began in December 2020 © Getty Images

What are the chances of someone having an allergic reaction to the vaccine?

Very small. Severe allergic reactions to vaccines are extremely rare, approximately one per million vaccine doses, according to research published in the Journal Of Allergy And Clinical Immunology. You have a similar chance of an allergic reaction to anything you put in your body, such as a new food.

Those with a significant history of such reactions (people who are required to carry an adrenaline pen at all times) should check with a healthcare professional before receiving an injection. This is the same advice given to those taking the seasonal flu vaccine.

“This is why, even though the risk is tiny, the vaccine is administered in some sort of healthcare-providing setting,” says Rossman. “Because you’re not going to get the jab and have a reaction six hours later; you’ll have it immediately and get care immediately. But the risk really is extraordinarily low.”

Is there a risk, however small, that the vaccine will accidentally give you COVID?

No, there’s no evidence that any approved coronavirus vaccine may inadvertently infect somebody with the virus.

It’s true that many past and current vaccines are manufactured by inserting a dead or inactive version of a virus into the body. But these have been shown to effectively and safely protect humans from diseases. The inactive rabies vaccine, for instance, is received by more than 15 million people each year, according to the World Health Organization.

But the Oxford/AstraZeneca and Pfizer/BioNTech vaccines aren’t produced by killing or deactivating the virus. “They only contain tiny instructions about how to build a tiny part of the virus, not the virus itself. So, there’s absolutely no chance of getting COVID from them,” says Rossman.

Some coronavirus vaccines, such as China’s CoronaVac, are being developed using inactivated viruses. But although the vaccine is easily stored at fridge temperature (2–8 °C), its widescale production could be problematic.

“To make a huge amount of a highly dangerous virus and then kill it – making sure it’s definitely dead – is a massive task,” says Matthews.

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Does the coronavirus alter your DNA?

The short answer: no, none of the coronavirus vaccines have been shown to alter human DNA. But it’s easy to see how a simple misunderstanding could form this fear.

“The mRNA vaccines, such as the Pfizer vaccine, work by giving genetic information (RNA) about how to make a viral protein to just a few of your cells,” says Rossman. “That sounds a lot like altering your genome. However, the RNA doesn’t mess with the DNA when in the cell – it’s its own entity that degrades very quickly but still generates an effective immune response.


“Ultimately, the vaccine is just a transient phenomenon, and not something that actually affects you permanently.”

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Thomas Ling
Thomas LingDigital editor, BBC Science Focus

Thomas is Digital editor at BBC Science Focus. Writing about everything from cosmology to anthropology, he specialises in the latest psychology, health and neuroscience discoveries. Thomas has a Masters degree (distinction) in Magazine Journalism from the University of Sheffield and has written for Men’s Health, Vice and Radio Times. He has been shortlisted as the New Digital Talent of the Year at the national magazine Professional Publishers Association (PPA) awards. Also working in academia, Thomas has lectured on the topic of journalism to undergraduate and postgraduate students at The University of Sheffield.