Fever, application site pain, and other post-vaccine symptoms: what they mean and how long they last

Unwanted side effects are known to come with all medications, and vaccines are no exception.

With the emergency authorizations in the context of the COVID-19 pandemic, the peculiarity occurs that the effects reported in the preliminary Phase III studies, are added those that appeared later after the mass vaccination of populations .

Currently around the world, a dozen vaccines approved by the World Health Organization (WHO) are applied, plus another handful which, although not supported by the body, are applied in some developing countries.

In Europe, four vaccines are administered after being approved by the European Medicines Agency (EMA): the medicines Pfizer / BioNTech, Moderna, AstraZeneca and Janssen. In addition to the four approved by the European Medicines Agency, the vaccines Sinopharm / Beijing Bio-Institute of Biological Products Co-Ltd, Sinovac, Sputnik V, CanSinoBIO, Novavax and Curevac are added to the list established by the WHO. the world.

One of the most used – because it is the first to receive authorization emergency – is that of Pfizer, followed by AstraZeneca.

In the latest pharmacovigilance report from the Italian Medicines Agency (Aifa), 204 reports of adverse reactions per 100,000 doses administered are mentioned, regardless of the type of vaccine and the severity of the disorder.

The most common were fever, fatigue, headache, muscle and joint pain, injection site pain, chills, and nausea. These are more common after the second dose of mRNA vaccines and after the first dose of AstraZeneca.

Very rare cases of atypical and intracranial venous thrombosis are also linked to the latter vaccine, a non-replicative viral vector (1 case per 100,000 first doses administered, no case after the second dose), mainly in children under 60 years of age. . The same effect has also been reported after the application of the Johnson & Johnson vaccine.

What effects can be expected on the day of vaccination (and the next day)

Regarding the mild and moderate effects, which represent 90% of the total, the reaction that occurred in most cases (83%) occurred on the same day of vaccination or the next day and more rarely the effect occurred within 48 hours.

After the mRNA vaccines -Pfizer and Moderna-, the most frequent reactions are fever, pain in the arms, fatigue and weakness, chills and general malaise, while the effects of viral vector vaccines (AstraZeneca, Sputnik and Janssen) change slightly: fever, fatigue and weakness, chills and pain at the injection site.

Many women have reported menstrual irregularities after vaccination, but to date there is no scientific evidence that the two phenomena can be linked.

To summarize, specialists agree in considering two very frequent effects (fever and pain in the arm) and a third, particularly troublesome: acute and persistent headaches.

Why does the arm hurt

Many people report feeling swollen in the arm where they received the puncture, as well as pain or seeing it red. There are also those who feel tingling in the place.

In the first place, Specialists specify that arm pain is more common with mRNA vaccines, that it is not perceived by everyone and that it is also common to other vaccines that are not against the coronavirus.

It can develop a few hours after the injection and last for a few hours or a few days. It is due to the activation of the immune system. The intensity of this activation can depend on several factors, such as age, gender and stress.

In some subjects the inflammatory state is more pronounced, but this does not mean that they have developed a stronger immune response than others who have not presented pain after injection. Sometimes arm pain is associated with swollen lymph nodes in the armpit area, which can last for a few days. All of these reactions are absolutely normal and have nothing to worry about, according to experts.

A US study looked at a unique skin reaction that can occur after vaccination with Moderna: an itchy, sometimes painful rash that lasts an average of five days. And as recommended, the injection area should not be massaged, even if the pain is severe, ice can be applied or consult the family doctor, or inform the specialist who performs the post-vaccination follow-up.

The cause of fever

However, the inflammation can go beyond the injection site and spread to other parts of the body, causing an increase in body temperature and general pain.

As mentioned, fever mainly occurs after the first dose in viral vector vaccines and after the second in mRNA vaccines.

It usually occurs within two days of vaccination and goes away within 48 hours.

In the event of severe discomfort, after consulting your doctor, you can take paracetamol or ibuprofen, according to the specialist’s instructions.

Why does he have a headache

A sharp and persistent headache after vaccination is not of concern. And if necessary, after consulting your doctor, you can take a pain reliever.

On the other hand, there are rare cases in which the headache should alert, but are easily recognized.

Likewise, it should be noted that the headache produced by cerebral thrombosis is peculiar and easily recognizable: it is a throbbing pain accompanied by neurological symptoms, such as difficulty moving and / or speaking, double vision.

Even in thrombosis of the veins of the abdomen (atypical site), extremely severe pain is felt in the affected part.

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