The adverse effects of vaccines that you don't have to worry about

Pain in the arm from the jab, fatigue, headache or fever are some of the most normal symptoms

3 min
A nurse vaccinating an essential professional in Hospitalet

BarcelonaRaúl Martínez, a sixth-year medical student at the University of Barcelona, received his first dose of the Moderna vaccine the day before starting his internship at a Primary Healthare Centre. "At first it didn't hurt or anything, but as the hours went by my arm started to ache a bit", recalls Martínez. The next day he went to work anyway, but on the day after he couldn't because he felt a little sick: he had a little fever, headache, general malaise and chills. "But it was nothing, I took a paracetamol and I felt fine", he says.

So, far from posing any danger, these adverse effects are normal and are fully foreseen in the technical data sheets of the vaccines. "All in order", says the director of preventive medicine at the Hospital de Bellvitge, Cristina Masuet. "People have to know -she continues- that the vaccine is effective and the safety is very high: we are not seeing serious cases". In fact, Masuet explains that the main adverse effect of those vaccinated in her hospital is simply pain in the arm of the jab: 90.2% of those who receive it are affected. "The messenger RNA and the technology used are completely new in the field of vaccines, but it had already been seen in clinical trials that it caused absolutely tolerable local pain", adds the director of the preventive medicine and epidemiology service of the Hospital de la Vall d'Hebron, Magda Campins.

As marked by the data from the questionnaires that the vaccinated have answered in the Hospital de Bellvitge and the technical data sheets of vaccines already mentions, fatigue, with 64%, is the second most common symptom. Lower stand the percentages of immunized people who, like Martinez, have suffered muscle pain and headache (30%) or a fever (12.4%). Moreover, according to Masuet, most adverse effects disappear after 48 hours and also disappear with the help, for example, of a paracetamol. Although it is recommended to take antihistamines or acetaminophen after vaccination, it is not recommended to do it before because it is not known if it can negatively affect the effectiveness of the dose.

There are also cases in which the body's reaction to the vaccine causes lymphadenopathy in areas such as the armpit, upper back, or neck. For this reason, Masuet assures that less than 3% of those immunized have come to the emergency room to be checked by a doctor as a precaution or because they did not imagine that the vaccine could be the cause. This is the case of Laia, who three days after being vaccinated, the pain of the first days in her arm spread to her chest. "I thought I had a contracture because I had carried a lot of bags, but I did a self-examination and I saw that I had a two-centimeter bump under my arm that was mobile and that hurt a lot", recalls Laia. "I went for an ultrasound", she continues, "and the doctor asked me if I had been vaccinated. It turned out that I was already the third patient who went because of that, but I didn't think of it".

Masuet explains that there are also those who are surprised by the pain in the arm because the Pfizer and Moderna needle, unlike other vaccines we are used to, is thinner and shorter and almost unnoticeable, but the pain appears after a while. "The tetanus vaccine, for example, hurts immediately", Masuet compares.

On the other hand, Campins explains that, within the percentages mentioned above, the second dose only causes more side effects than the first and that there are already studies that indicate that those who have had the coronavirus, at least symptomatically, tend to have stronger reactions to the vaccine. "Beyond the natural immunity of those who have passed the covid, this is one of the reasons why the Health Department has decided to delay the vaccination of those younger than 55 years who already have antibodies until six months after being infected", Campins says.

However, the pharmacologist and member of the technical committee of pharmacovigilance of the Hospital Clínic Joaquín Sáez recalls that all vaccines that are administered have risks and benefits. "In this case, and always, the balance is very clearly in favour of the benefits", says Sáez. He also points out that the type of adverse effects and the percentage of cases are very similar to those of clinical trials. "In this sense, we can now say that 'everything will be fine'", Sáez jokes.