Mass vaccinations against the SARS-CoV-2 virus are picking up pace in more and more countries around the world. In Spain there are already more than 1.3 million people vaccinated (around 2.8% of the Spanish population) with two doses of the Pfizer, Moderna and AstraZeneca vaccines.
Among people who are going to be vaccinated soon or among those who have already received a dose recently, doubts often arise about different issues. Next, we are going to clarify those most frequent questions that appear about vaccination, because sooner or later we will all go through this process and many of these questions will be asked again and again.
So far, all the data provided by clinical trials and vaccination experiences in the real world on hundreds of millions of people indicate that the adverse effects produced by different vaccines against COVID-19 are equivalent to the reactions that we find with other vaccines. many vaccines marketed for decades.
Although the adverse effect profile is slightly different for each coronavirus vaccine, in practice their most frequent (and mild) adverse effects are practically the same. In addition, it has been observed that the chances of suffering these effects increase when the second dose is received (with those vaccines that require two doses for adequate immunization) or when the coronavirus infection has been passed before and the vaccine is received.
Depending on which vaccine it is and whether it is the first or the second dose, between 4 and 8 people in 10 who are vaccinated against the coronavirus will experience one or more minor and temporary adverse effects (hours or days of duration). These effects usually begin to appear within 8-12 hours of receiving the vaccine and last a maximum of 48 hours. The most common are: swelling and pain at the injection site, fever, headache, joint or muscle pain, fatigue, dizziness, nausea and chills. Some people describe the post-vaccination experience as something akin to getting the flu or having a hangover.
Serious allergic reactions (anaphylaxis) can appear among the serious adverse effects that have been documented, although they are extremely rare: around 2-5 cases per million population for the Pfizer and Moderna vaccines.
Almost all the adverse effects that occur when receiving the vaccine are ‘collateral’ effects of the activation of the immune system against the molecules of the coronavirus, which are part of the vaccine. Therefore, when receiving the second dose there is a greater probability of negative effects because the response of this defensive system will be more robust and powerful, since it is the second time that it is exposed to the same molecules.
Fever, fatigue, chills, headaches … arise as a result of a complex biochemical cascade in our body in which molecules such as prostaglandins and inflammatory cytokines and cells such as macrophages intervene. They are reactions that also occur in infections and that occur to improve the effectiveness of the immune system against various microorganisms. In the case of vaccines against COVID-19, there are no functional coronaviruses, but only key fragments of these that will serve as “hallmarks” for the immune system to activate and recognize them.
Does that mean that a person who has not had any adverse effects is not immunized against the coronavirus, since this would indicate that the immune system has not responded? Absolutely. In fact, we know from multiple clinical trials that a portion of vaccinated people do not experience any adverse effects and are equally protected against COVID-19. The point is that the response of the immune system of each person can be very variable in terms of its external manifestations. In some people this system can react in a somewhat “scandalous” way, with fever and significant fatigue, and in others the immune system will do its job with measure and without attracting attention and individuals will have at most a little pain in the area. of the puncture and little else.
If adverse effects such as fever, headache or muscle pain appear and you want to relieve symptoms, the most recommended option is paracetamol 650 mg every 6 hours. If, for allergy or other medical reasons, this option is not the most advisable, another good option is 400 mg ibuprofen every 6-8 hours. Both paracetamol and ibuprofen are antipyretic (act against fever) and analgesics (against pain). Ibuprofen is also anti-inflammatory. In any case, paracetamol has a slightly higher safety profile than ibuprofen and that is why it is usually recommended as the first option. Both drugs in these doses do not need a prescription.
However, at this time there is some controversy about the consumption of paracetamol or ibuprofen before receiving the vaccine to avoid the possible appearance of adverse effects, that is, as prophylactic use. Studies previous have observed that the prophylactic administration of antipyretics (like the previous drugs) affect the immune response to various vaccines (such as whooping cough, tetanus, etc …). Since almost all COVID-19 vaccines have been evaluated in clinical trials without participants taking medications such as paracetamol or ibuprofen in advance, we cannot know if taking them could affect their effectiveness. This is why it is generally not advised to take such drugs before receiving COVID-19 vaccines.
However, the Ministry of Health does add an exception to the previous general recommendation: the AstraZeneca vaccine. The reason? We have a clinical trial in which it was observed that the ingestion of paracetamol before receiving this vaccine did not alter the immune response.
In the document “Vaccination strategy against COVID-19 in Spain” of February 26 it can be read: “Frequent mild local and systemic reactions are observed after vaccination. Doses of 1 gram of paracetamol can be used prior to vaccination, followed by 1 gram every 6 hours during the first 24 hours, which reduces significantly local pain, low-grade fever, chills, myalgias, headache and postvaccinal discomfort, without influencing the immune response “.
However, the recommended amount of 1 gram every 6 hours is far from optimal for preventing fever and pain in the general population for three reasons. First, because 650 mg paracetamol it has a much more favorable efficacy and safety profile: lower risk of adverse effects with similar efficacy for treating fever and pain. Second, not all people who will receive the Astrazeneca vaccine will have to suffer pain or fever, so this recommendation encourages the medication among people who do not need it. If we take into account that paracetamol takes between 40 and 60 minutes orally to take effect, a more prudent option would be to wait and see if the adverse effects appear to decide if it is treated with 650 mg paracetamol or not.