¿Debes preocuparte por los efectos secundarios de las vacunas?

It should go without saying that vaccinations are a crucial part of staying healthy. Whether we're talking about routine injections in childhood, or travel jabs before you go abroad, vaccinations can protect you against any number of potentially deadly diseases. Importantly, since you won't be able to pass on those diseases, it also protects those around you.

Unfortunately, getting the facts right about vaccinations can mean sifting through a lot of misinformation. This year, the UK saw a sharp rise in cases of sarampión, which public health experts have linked to a drop in the number of children receiving the vacuna MMR jab (for measles, paperas y rubéola).

They suggested the drop might be due, to a large extent, to 'anti-vaxxer' myths on discussion boards. One of these is the idea that the MMR vaccine causes autismo. While this theory has been thoroughly and repeatedly debunked, it continues to rear its head on social media.

As Gino Martini, chief scientist at the Royal Pharmaceutical Society points out, this trend is extremely worrying.

"How many of the people on the discussion forums are actually medical doctors with the right advice?" he says. "We're getting into a situation where people aren't getting the information. People go on Facebook and have conversations, and suddenly they aren't vaccinating anymore. This is important because the diseases we're trying to prevent are very nasty."

What are the risks of getting vaccinated?

While vaccinations can cause side effects, these effects are typically very mild, and the risks associated with contracting the disease far outweigh the risks of getting vaccinated.

"You might experience resfriado-like symptoms, a high temperatura, or aches and pains," says Martini. "Those are the kinds of adverse events you see while your body adapts to the vaccination. You may also experience some pain at the site of administration."

Vaccines work by introducing a small amount of bacteria, virus or toxin into the body. Because the bacteria, virus or toxin have been killed or weakened, there's no risk of contracting the disease in question. However, your body responds as if it were under attack, and mounts an immune response. If, in the future, you do encounter that disease, you'll have an army of antibodies ready to fight it.

This means that any adverse effects you experience are unlikely to be caused by the bacteria, virus or toxin. Most of the common side effects (such as a sore arm or redness) are caused by the injection, or by your own immune system fighting against the weakened invaders.

The risk of even mild reacción alérgica to the vaccine is small. In this case, you're more likely to be reacting to one of the added ingredients than to the virus. The person administering the jab will ask you about allergies first - egg protein and pork gelatine are possible culprits.

What are the chances of serious side effects?

Serious adverse events, while possible, are very rare - and they tend to make the news precisely because they're so unusual. You may have read reports last year about two people who died after receiving the yellow fever vaccination. If you're considering getting the jab, this tragic news needs to be viewed in context.

According to the Organización Mundial de la Salud, serious side effects occur at a rate of around 0.09 to 0.4 cases per 10,000 doses of the yellow fever vaccine, in populations who haven't been exposed to the virus. By contrast, the serious form of yellow fever is fatal around half the time.

On a similar note, the rate of serious allergic reaction is around 1-2 cases per million across all vaccines. Compare that with the death rate for measles (around 1 in 500), and for flu (around 200 deaths in the UK every winter), and it's obvious which is riskier.

"What we need to understand are the risks and benefits - how many people are dying from yellow fever, how many people are dying from measles?" says Martini. "Clearly, adverse effects are tragic for the individual and the family but they are rare, and we need to balance this with the risks associated with that disease."

Multiple vaccines - double the trouble?

Another important question is what happens when you get multiple vaccinations. If you're going travelling, for example, you may need five or more injections at once. And in the UK, a two-month-old baby will receive the PCV, Rotavirus, 6-in-1 y MenB vaccines on the same visit.

Of course, being injected isn't fun, and being repeatedly injected is even less fun. Your arm may be sorer than it would be with a single vaccine. And if you start to feel unwell during any point in the process, you should stop and seek advice from the person administering the vaccine.

However, you don't need to worry about some kind of compound side effect, or overloading the sistema inmunológico. Even a baby's immune system is well equipped to cope, and is exposed to many times more antigens every day than those contained in any vaccine - multiple or otherwise. Avoiding multiple or combination vaccines will only draw out the process.

If you're still on the fence, it's important to remember that vaccinations prevent up to three million deaths worldwide every year, and the introduction of vaccination programmes has wiped out many diseases that used to be killers.

On top of that, your pharmacist, nurse or doctor should be able to help you with any concerns that arise. As Martini explains, they're there to put your mind at rest, and walk you through what to expect, This will always include information about possible side effects.

"If you’re worried, the first port of call is always to talk to the pharmacist or nurse. They'll be able to advise you," he says. "They'll look at the vaccine and the manufacturer's advice, because it's information that can help the patient and reassure them."