See the reactions that may arise with the third dose of Covid vaccine

Covid vaccines have been approved and have been used around the world for nearly a year and, in addition to the phase three studies, when the safety profile of the immunizers was tested, the observation of their use in more than three billion people proves this safety .

Despite this, most vaccines were evaluated with a primary vaccination course in two doses or a single dose from the same manufacturer. Now, the application of a booster dose of vaccines is growing all over the world, which can be with the use of an immunizing agent different from the one applied initially.

In Brazil, the Minister of Health, Marcelo Queiroga, announced on the 16th that all Brazilians aged 18 or over will receive a booster dose of immunizing agents, preferably from Pfizer. It is possible that doubts arise, then, as to the types of symptoms that may appear with the application of the third dose, even more if it is a vaccine different from the first, in the so-called heterologous scheme.

Vaccine mixture studies prove the efficacy and safety of the combination of immunizers, but some vaccine mixtures have not yet been tested or, if they were, there is not yet enough data to indicate the possible side effects that may arise. This is the case of an application of a booster dose of Pfizer to individuals who received Janssen’s vaccine, for example.

Experts in vaccines and immunology emphasize, however, that there is no evidence of a higher incidence of adverse events when mixing the immunizers in the booster dose. On the contrary, the occurrence of side effects can be even smaller. “There is no expectation that the application of a booster dose with the interchangeability of the platforms will increase the incidence of adverse events”, says infectologist Jamal Suleiman, from Instituto Emílio Ribas.

It is possible, however, that Brazilians now experience an effect with the third dose, related to the type of immunizing agent, which was not felt at the beginning. Side effects, experts stress, are generally very mild and pose no danger.

“The risk of a totally unexpected adverse event arising in the booster dose is lower, but we have to remember that vaccines from another platform are offered than in the primary regimen, so we expect side effects already expected for these immunobiologicals to occur”, says the infectologist Eder Gatti, from the Center for Epidemiological Surveillance of the State of São Paulo.

Also according to Gatti, the risk is reduced because the immune system has already been introduced to the antigen, that is, the virus or part of it, and the additional dose has the function of “refreshing the body’s memory” to create a defense against the pathogen. “Nevertheless, Pfizer’s, by using the messenger RNA that encodes the virus’s protein S, can give a slightly stronger reaction in the booster dose than in the first doses”, he says.

Some reports heard by the reporter indicated the occurrence of swelling in lymph nodes, especially those located in the armpit region of the arm in which the third dose of Pfizer was applied, the so-called inguas, on the first to the fourth day after the injection.

According to the package insert of the Pfizer vaccine at Anvisa (National Health Surveillance Agency), the enlargement of lymph nodes (or bulges) is an uncommon adverse reaction, with an incidence of 0.1% to 1%.

A study published in June in the journal Jama Network found axillary lymph node swelling to occur in 13% of participants evaluated after injection with two doses of the mRNA vaccine—12% for Pfizer vaccinates and 17% for Moderna.

The incidence of swelling is more frequent after the second dose (26%) compared to the first (5%). Typically, lymph node swelling is noticed from the second day onwards and disappears within four days of the injection.

The most common symptoms after the third dose are still those known for the initial doses: pain at the injection site, myalgia (pain in the body), tiredness, headache, fever, chills and swelling at the injection site.

Other common but not as frequent reactions are nausea, vomiting, diarrhea, bruises and redness on the arm, high fever, excessive sweating and itchy skin.

“So far, we have not had any reports of swellings with patients here in the unit, but it is very common — I would say that 9 out of 10 patients — experience pain in the arm after the third dose”, says Carla Dias, nurse and supervisor vaccination against Covid at UBS Milton Santos, in the south of São Paulo.

At the same health facility, a 56-year-old healthcare professional, who declined to be identified, received the additional dose from Pfizer. The nursing assistant at the unit says that it can happen to have a “swelling or turning purple” at the injection site. “We are already warning you in case you appear to make an ice pack in the region where the vaccine was applied and the use of common analgesics”, says Dias.

Other reports of bruises, body aches and tiredness were also shared with the report. Despite being local or systemic reactions that can be quite intense, such as severe pain in the arm and the impossibility of moving it, they usually disappear within 24 to 48 hours, says Suleiman.

“It is not an adverse event that makes it impossible to work, that limits the routine, so it is not necessary to communicate it to the health system”, says the doctor, who also received the booster dose from Pfizer. More serious cases, he says, are mandatory notification. In this case, patients in SP can contact Emilio Ribas’ outpatient clinic via email

Speech therapist Claudia Lima, 50, reports that she had an adverse reaction after the booster dose of Pfizer. She took both doses of AstraZeneca and had no reaction, but with the additional dose of messenger RNA she had symptoms that lasted for ten days: fever, vomiting, diarrhea, pain throughout her body, and a reaction at the site of the vaccine. “Despite this, however unpleasant they may be at the moment, the effects of vaccination are not even close to the suffering caused by the disease”, he says.