How to get rare side effects of coronavaccins

The first coronavaccins have arrived in the Netherlands, on 8 January the first shot will be made. From that moment on, we slowly build up more protection against the coronavirus, but we also have to deal with side effects. What can we expect? And how do we get to see very rare side effects?

Side effects are a logical consequence of vaccinations. Vaccines put our immune system to work so we can handle new pathogens. That could cause discomfort for a moment. The benefits of vaccines must always outweigh the disadvantages.

Known side effects

Common side effects are quickly identified during studies with volunteers. For example, PFIZER/BionTech involves pain at the injection site (75 percent reported this side effect), headache (39 percent) and fatigue (37 percent). Usually the complaints lasted 1 to 2 days.

Because vaccines are tested on tens of thousands of people, rarer side effects are also revealed. For example, in the PFIZER study, some vaccinees developed sleep problems. Researchers recorded that in their report as uncommon, which means that it occurred in 0.1 to 1 percent of vaccinated subjects.

Not everything in the picture

Not all side effects may appear during the studies. In Pfizer‘s major study, about 22,000 people received the vaccine. โ€œA study of this size basically shows the side effects that occur in more than 1 in 7000 people,โ€ said Sabine Straus of the Pharmacovigilance Committee (PRAC) of the European Medicines Agency (EMA). So there is a real chance that new side effects will come to light if you vaccinate hundreds of millions or even billions of people.

Think, for example, of the serious allergic reaction that occurred in a number of people in Britain after receiving the approved vaccine. Because of that side effect, the EMA now recommends monitoring people for 15 minutes after the shot.

The main way to identify rare side effects is through notifications from citizens and caregivers. Dutch people can report suspected side effects to Side Effects Centre Lareb.

Lareb is focused on reports of serious or unknown complaints. The main question is always whether the complaints are the result of vaccination. โ€œThere will no doubt be people who will get complaints right after a shot,โ€ says Lareb Director Agnes Kant. โ€œThat does not always mean that there is a connection with the vaccine. There may be other explanations as well.โ€


In order to better determine if there are rare side effects, Professor Miriam Sturkenboom of the UMC Utrecht has calculated how often they occur in the European population for 38 diseases. She did this for, among other things, sleeping sickness narcolepsy, severe allergic reactions and for syndromes that also occur with covid-19.

โ€œ If there are signs of possible side effects, we can quickly calculate whether the condition occurs more frequently after the administration of a coronav vaccine. And if so, how many more oftenโ€, says Sturkenboom.


If Lareb detects serious side effects, the side effects centre informs RIVM and the Nederlandse College for Evaluation of Medicines (CBG). They may, if necessary, send warnings to doctors, the Ministry and other stakeholders. The CBG can also ensure that action is discussed at European level.

At each signal, the EMA reviews whether the pros and cons of the vaccine are still in balance. The EMA itself also has a committee that monitors side effects from around the world and examines worrying signals. In addition, new information from pharmaceuticals is regularly received. โ€œThey should investigate reports of their vaccines,โ€ says pharmacovigilant Straus. โ€œReports of serious side effects must be reported to us within 24 hours. And they need to carry out follow-up studies and report on them.โ€


With new side effects, the EMA can take various actions, says Straus. โ€œPharmaceuticals must regularly update their leaflets to add additional side effect or to dissue their medicine for a specific group. It also happens that we temporarily stop the use of a remedy. In the extreme case, we will definitely remove resources from the market.โ€

Decisions of the EEA come to our puncture sites via the CBG and the RIVM. โ€œIf the vaccine is not recommended for certain groups, we will adapt our protocols,โ€ says Hans van Vliet, manager of the RIVM National Vaccination Programme. โ€œAnd if the EMA has to remove a vaccine from the market, it’s the end of the story here too.โ€

When all the rare side effects of the coronavaccins are on the table is unclear. This depends partly on how rare any side effects are and how quickly the vaccineswill be rolled out. It is clear that several agencies monitor whether the balance between effectiveness and risk remains in order.