See possible side effects with fourth dose of Covid vaccine

With the recommendation of the fourth dose of vaccine against Covid-19 for those over 40, doubts may arise about the side effects of immunizations.

After all, what are the expected reactions for these products? Can the fourth dose —or second booster— bring any specific reaction? Why do side effects occur?

THE Sheet spoke with experts to answer these and other common questions.

What reactions are expected when someone is vaccinated against Covid?

The main effects of the four vaccines used in Brazil –Coronavac, Janssen, Pfizer and Astrazeneca– are pain at the injection site, feverish sensation, malaise, body ache and flu. Typically, these symptoms disappear within 24 hours, at most they can last for two days.

Reactions like these are already known for other immunizers and medicines. “I suggest reading the leaflet of some antipyretics to see the reactions that some of them can cause”, says Isabella Ballalai, vice president of the Brazilian Society of Immunizations (Sbim).

Also, not everyone has these symptoms. According to the leaflet of immunizers, most of these milder symptoms can be felt around 10% of those who use the drugs.

“Most people have nothing, and these are absolutely normal reactions and simply mean that the immune system is reacting to the vaccine,” says Cristina Bonorino, immunologist and professor at UFCSPA (Federal University of Health Sciences of Porto Alegre).

Some more unusual reactions may occur. The Pfizer vaccine package insert, for example, states that 0.1% to 1% of people who used the immunizer had insomnia, intense physical fatigue, night sweats or hives (skin allergy with severe itching).

Like Pfizer, the other three vaccines can have very unusual adverse reactions. “None of them cause major problems”, says Marcos Boulos, professor of infectology at the USP School of Medicine (University of São Paulo).

Can the fourth dose of a vaccine bring any side effects different from other applications?

There is no evidence that a fourth dose results in effects other than those seen previously. In this way, what is already known and documented in the product package inserts is maintained.

“Usually, with each dose of vaccine, not just Covid, the chance of an adverse event is lower. The first dose is usually the most reactogenic”, says Ballallai.

Cases in which these effects can occur in additional doses, as in the fourth application, are usually when a different vaccine is used from the others already applied – a scheme called heterologous.

“The heterologous regimen may have more adverse events, but they are mild reactions,” adds Ballallai.

Why can vaccines cause side effects?

It is often understood that feeling a reaction after vaccination means that the immunizer is working. The reality, however, is not so simple.

“The fact that you have an adverse effect in general is an indication that the vaccine is working, but if you don’t feel it, it doesn’t mean that the vaccine doesn’t work,” says Bonorino.

She explains that each person has a so-called innate response, “which is an initial inflammation that precedes any response that will generate immunological memory.” It turns out that some people may be more sensitive to feeling the symptoms and others not so much.

Another factor that influences the emergence of reactions is the technology used in each vaccine. Boulos says that those with the adenovirus platform – which uses a virus that carries the genetic code of Sars-CoV-2, the pathogen that causes Covid-19 – are the ones that can cause the greatest adverse effects.

“The people who complain the most have probably taken the adenovirus vaccines. They are those who inject a specific virus, which although it does not cause almost anything, it can have some small side effects”, says the infectologist, reiterating that the effects, when senses, are still quite light.

In Brazil, Janssen and Astrazeneca vaccines are produced using this technology. In addition to the adenovirus platform, there is messenger RNA (Pfizer) and inactivated virus (Coronavac) technology. They can also have adverse effects, but they are still very mild and in most cases disappear soon.

Are there more serious side effects?

In general, vaccines used in booster doses have a similar profile in causing common adverse effects that do not last more than two days. Janssen’s vaccine has a history of causing a rare syndrome related to potentially deadly blood clots. A similar situation has already been documented for Astrazeneca.

The occurrences caused the US Food and Drug Administration (FDA) to limit the use of Janssen’s vaccine in the country, but it is still available for application. In Brazil, Anvisa (National Health Surveillance Agency) evaluated that the benefits of the immunizing agent outweigh the risks, which are very rare.

In the vaccine package insert, Janssen says that cases are rarely documented, but it is important to seek medical attention and inform the healthcare professional that you have had the vaccine if you experience symptoms such as severe or persistent headaches, seizures, changes in mental status, vision cloudiness, unexplained bruising outside the vaccination site that appears within a few days, small rounded spots on the skin outside the vaccination site, shortness of breath, chest pain, leg pain or swelling, or persistent abdominal pain.

The package insert also says that it is possible to report the presence of side effects through the national notification system.

For Ballallai, the syndrome is very rare and the vaccine, like the others approved, has a high safety profile documented through clinical studies and also by the many doses that have already been applied.

“So far, for all these vaccines, the safety profile is excellent with very rare cases of adverse events that we consider serious. There is no reason to consider that vaccines against Covid are dangerous”, he says.

She also says that not all adverse effects, especially the most serious ones, are causally related to vaccines. In these cases, it is important to carry out investigations in order to find out if there is any association between the immunizing agent and the reaction.

Do side effects indicate that vaccines are unsafe?

As explained above, there are a few reasons for the appearance of adverse events. One is the technology used by the vaccine and another is the indication that the immune system is reacting to the immunizer.

No adverse events, however, indicate that vaccines are unsafe. An indication of this is the clinical studies carried out that measure the safety of immunizers.

Another great indication of the safety of these products currently used against Covid-19 is that they have already had a high dose of application, but with very few reports of serious reactions.