Categories: Side effects

Side Effects of COVID-19 Vaccine

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Discover the Side Effects of COVID-19 Vaccine.

If it’s your turn to get vaccinated against COVID, learn about the most common side effects of the Pfizer, Moderna, Janssen, and AstraZeneca vaccines, how to ease their discomfort, and what serious symptoms you should be on the lookout for.

More than half of the American population already has at least one dose of the COVID-19 vaccine. Side Effects of COVID-19 Vaccines

And it is that, in recent weeks, due to the increase in the doses received and the rebound in cases in some areas, the rate of vaccination has accelerated, although not only in America, many countries have been underway to immunize its population as soon as possible.

This has made the topic of vaccines one of the most commented in WhatsApp groups or tabletop gatherings. What vaccine have they given you? Have you had any side effects of the covid-19 vaccine? How long do they last?

These are some of the most frequent questions that all immunized people ask themselves these days.


With data from the AEMPS Pharmacovigilance report on COVID-19 Vaccines (Spanish Agency for Medicines and Health Products), which reflects the notifications of adverse events registered among those vaccinated in Spain until June 11, and with the help of an expert in clinical pharmacology, in this article, we analyze in detail which are the most common reactions after receiving each of the four vaccines approved in our country and how to improve your symptoms.

The most common side effects of the covid-19 vaccine are mild-moderate in intensity and disappear in less than 72 hours after injection.

The most administered vaccines are those of the mRNA type, that is to say, that of Pfizer-BioNTech and that of Moderna, however, a large number of doses of that of AstraZeneca and Janssen have also been injected.

Although all are approved in Europe and usually have similarly mild side effects, the probability of suffering them varies between each one.

The Dra. Cristina Avendaño Solá, a specialist in Clinical Pharmacology of the Hospital Universitario Puerta de Hierro, explains that “in general, all vaccines of the COVID share the most common side effects and these are mild to moderate intensity and resolve spontaneously in less than 72 hours ”.

The most common are fever and pain in the arm in the area of the puncture, dizziness and headache, and musculoskeletal discomfort.


Remember that, as soon as you receive the vaccine, it is advisable to wait 15 to 30 minutes at the vaccination site to be able to be treated in case of presenting an unexpected immediate reaction.

When mild symptoms occur, in more than 80% of cases they appear on the day of vaccination or within 24 hours.

Side Effects of the Pfizer-BioNTech Vaccine

As indicated in the 6th Pharmacovigilance Report on COVID-19 Vaccines of the Spanish Agency for Medicines and Health Products (AEMPS), the Comirnaty vaccine from BioNTech / Pfizer, messenger RNA type, requires two doses, separated by 21 days, and Its most frequent side effects along with the prevalence of each symptom are:

Fever: 38%

•Headache: 28%

•Muscle pain: 21%


•Swelling and pain at the vaccination site: 15%

•Upset: 12%

•Fatigue: 8%

•Nausea: 8%

•Joint pain: 8%

•Chills: 8%


•Lymphadenopathy (swollen lymph nodes): 8%

Dr. Avendaño adds that it is also normal to have diarrhea and vomiting, which usually do not last long.

Side effects of the Moderna vaccine

In this case, Moderna’s vaccine

, also of the mRNA type and with two doses, is injected with a separation time of 28 days or a month, and the symptoms that may be experienced after administration are:

Fever: 50%

•Headache: 32%

•Muscle pain: 24%


•Swelling and pain in the vaccination area: 18%

•Upset: 12%

•Chills: 12%

•Nausea: 10%

•Fatigue: 9%

•Joint pain: 9%


•Asthenia: 6%

In addition, recently, diarrhea and delayed-onset local reactions have been added to the SmPC and package leaflet as possible adverse reactions.

There may be a skin reaction several days later at the injection site, this occurs especially in the Moderna vaccine and does not mean that the second dose should not be administered, explains Dr. Avendaño.

AstraZeneca Vaccine Side Effects

In this case, the Vaxzevria vaccine is of the adenoviral vector type, that is, it contains a modified version of another virus that acts as a vector and indicates how the cells should proceed in case of infection.


The separation between doses is between 10 and 12 weeks, the longest of all. These are the most common side effects:

•Fever: 57%


•Headache: 41%

•Muscle pain: 26%

•Chills: 15%

•Upset: 14%

•Swelling and pain at the vaccination site: 11%

•Fatigue: 10%


•Nausea: 10%

•Dizziness: 9%

•Joint pain: 7%

Less common are other flu-like symptoms, such as sneezing, nasal congestion, muscle weakness, back pain, tremors, or hyperhidrosis.

This vaccine has been one of the most questionable due to the frequent cases of mild or transient thrombocytopenia – formation of blood clots in the blood vessels with low levels of platelets in the blood – and, above all, due to deaths recorded by thrombi after application.

For this reason, the administration of the AstraZeneca drug was suspended for a time in people under 60 years of age, however, it has been resumed after estimating that its benefits outweigh its risks.


In any case, systemic capillary leak syndrome (CFSS), urticaria, and angioedema have been identified as new adverse reactions in the Vaxzevria label and package insert, while signs related to immune thrombocytopenia and acute macular neuroretinopathy continue to be evaluated.

Janssen vaccine side effects

The Janssen vaccine, a Belgian subsidiary of the North American company Johnson’s & Johnson’s, has been the last to be approved in Spain.

This drug, of the adenoviral vector type, is single-dose, that is, it only requires one injection to complete the entire regimen. The AEMPS indicates that the most common side effects are:

•Fever: 29%

•Headache: 27%

•Muscle pain: 20%


•Dizziness: 9%

•Upset: 9%

•Swelling and pain in the vaccination area: 7%

Nausea: 7%

•Joint pain (arthralgia): 6%

•Fatigue: 6%


•Pain in the injection site: 6%

The technical data sheet and the package insert already include recommendations for better identification of the cases of thrombosis syndrome with thrombocytopenia that could present in the three weeks after vaccination.

On August 5, the Pharmacovigilance Risk Assessment Committee (PRAC) of the European Medicines Agency (EMA) updated the information on the Janssen vaccine and indicated that there is a causal relationship between its administration and cases of immune thrombocytopenia, dizziness, and tinnitus notifiable, for which it has recommended that these risks be included in the package leaflet and the technical data sheet of the vaccine, although it indicates that the benefit-risk balance of the drug remains positive.

In the case of thrombocytopenia, the PRAC has recommended that it go from being “a potentially significant risk” to “an identified significant risk”.

How to improve symptoms after the COVID-19 vaccine

If you have already been vaccinated and are beginning to feel some of the mild or moderate side effects of the drugs, such as fever, headaches, muscle or joint pain … do not worry.

Dr. Avendaño explains that commonly used analgesics or antipyretics such as ibuprofen or paracetamol can be taken, as would occur in any other vaccine, every 6 hours from the onset of symptoms. It is also advisable to drink plenty of fluids in case of fever.


In the case of discomfort, redness, or swelling at the injection site, the Centers for Disease Control and Prevention of the United States (CDC) recommend placing a clean, cold, and damp cloth or ice in the area to calm it about 2 or 3 times a day, as well as exercising the arm with regular movements so that the muscle recovers from the puncture.

It was also said that it was advisable to take paracetamol before and after going to be vaccinated with the AstraZeneca vaccine, but “it is not generally advised to take paracetamol or any other type of analgesic or antipyretic in a systematic way before vaccination.

This is because no medicine is harmless and since the symptoms are not serious and are quickly relieved by taking the medicine after the onset of symptoms, it is preferable to take them only when symptoms appear.

Furthermore, with other vaccines it has been seen that previous administration could even reduce the response to the vaccine ”, clarifies Dr. Cristina Avendaño.

Even so, the Vaxzevria Technical Guide provided by the Interterritorial Council of the National Health System reports that “paracetamol can be used as prophylactic treatment (before vaccination) and symptomatic (during the first 24 hours) to reduce these symptoms. that its use interferes with the immune response ”.

Intensity and duration of post-vaccination symptoms

Keep in mind that the effects after receiving the second dose may be more intense than those experienced after the first injection, but as indicated by the CDC you should not worry, since “these side effects are normal signs that your body is generating protection and they should disappear after a few days. “


In any case, although these symptoms are usually mild and disappear within 72 hours, contact your doctor if the irritation or sensitivity in the injection area worsens after 24 hours, or if in general any of these side effects do not disappear after a few days.

Also keep in mind that, after being vaccinated, the body may take between several days and weeks (depending on the vaccine received) to acquire immunity against SARS-CoV-2, so in that time it is possible to become infected with the coronavirus and present symptoms of COVID-19 because not enough time has passed to be protected, hence it is necessary to follow the usual protection measures against infection (use of a mask, maintain a safe distance, wash hands …) and See your doctor in case of symptoms of the disease.


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