Second COVID-19 vaccine shot: side effects, why they occur and how to treat them

Both the Pfizer-BioNTech vaccine and the Moderna vaccine are given in two doses, and it is important to get both shots. If you do not get a second vaccination, protection against infection will be incomplete.

The Pfizer-BioNTech vaccine is administered in two doses, 21 days apart. The Moderna vaccine requires two shots 28 days apart. You should receive the same manufacturer's vaccine (either Pfizer or Moderna) the first and second time, and be sure to receive the second dose on the recommended schedule. You will make an appointment for your second dose at the same time as your first dose appointment.

Will I have side effects after the second dose?

Side effects are more likely to occur and may be more noticeable after the second dose of the vaccine. The Pfizer-BioNTech and Moderna vaccines have almost the same side effects, but they don't last long—one to three days. The most common side effects include arm pain, weakness (feeling tired), headache, aches and fever. Side effects are a good sign: they indicate that the vaccine is working and priming the immune system. Serious side effects are rare and can be treated.

If possible, get vaccinated before the weekend in case you need extra rest after your second dose. Do not forget that you must strictly adhere to the recommended vaccination schedule . The second dose of the Pfizer vaccine should be received exactly 21 days after the first, and the second dose of the Moderna vaccine should be received exactly 28 days after the first.

A third dose of the COVID-19 vaccine is recommended for people with cancer and weakened immune systems.

You may have heard that the CDC is recommending a third dose of the COVID-19 vaccine for people who are immunocompromised, including some people with cancer.

Learn more

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What are the side effects?

If you experience side effects, this is a good sign. They indicate that the vaccine is working and triggering the immune system.

After the first shot, your immune system recognizes something foreign. The immune system automatically launches a mild attack against it. This process teaches your immune cells to recognize and respond to invaders. This is why you may experience side effects.

After the second shot, your immune system begins this attack again. But this time, more immune cells are activated, ready to launch a much more serious attack. This is why you may experience more side effects after the second dose. But they will disappear in a day or two. Think of it this way: the body's response to a vaccine is similar to training for a real fight.

If you were to become infected with the virus that causes COVID-19 after being fully vaccinated, your immune system would be prepared to mount an even larger and more powerful attack to protect you.

If you don't have side effects (after your first or second dose), it doesn't mean the vaccine didn't work. In clinical trials of the vaccine, more than half of the participants did not experience any side effects, but we are confident that the vaccine works effectively in these people.

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Ancha Baranova, professor at the School of Systems Biology at George Mason University:

“Everything “unknown and frightening” is divided into three types. The first is thrombosis, which does not just appear out of the blue. You need a predisposition. Thus, the risks increase in women who take oral contraceptives without a doctor’s prescription and prior testing. Women on hormone replacement therapy should also be identified. Although the fears here are unjustified, because HRT today is microdose. In addition, some people have conditions that predispose them to blood clots, but in this case, patients usually know about it. If you are worried that you will develop a blood clot, do not expose yourself to long flights in the first three days, as this is a precipitating situation.

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Fake instead of vaccination

The second is Guillain-Barré syndrome, which involves nerve damage and tissue numbness of varying severity. People often experience numbness in their arms after vaccination. But that's normal, no big deal! I became numb - and stopped! No consequences. But patients are nervous, they think: “Aha, Guillain-Barre has begun.” It manifests itself completely differently. It is a warning sign if numbness extends to both sides of the body or to the lower extremities and you are unable to walk. Any doubts? Go to the doctor, this is the best way to dispel anxiety.

The third is Stevens-Johnson syndrome, which is a skin reaction with inflammation. A super rare case, also of an immune nature. Dermatologists often overlook it, so if you notice something like this, say the name of the syndrome out loud when talking to your doctor.

Both conditions can occur as a reaction to any vaccine, not just coronavirus. It doesn’t happen that a person is initially healthy, then gets vaccinated, and that’s it! Without vaccination, the consequences of contracting Covid would be depressing.

I want to convey the main idea. Don't call side effects side effects, they are just effects after vaccination. When you buy protection against coronavirus, you have to pay for it. In this case, activation by the immune system: temperature, for example, and a very, very small probability of serious consequences.

I would compare the desire to refuse vaccination because the drugs are supposedly not fully studied and the consequences are unclear with the following statement: “I will never drive a car. What if I get into an accident!” But even as a passenger, you risk becoming involved in an accident, but not inside the car, but outside, where there is no such protection. A collision with a vehicle is more dangerous for the passenger than for the driver behind the wheel.”

Can I treat the side effects?

If you experience pain or discomfort after getting the vaccine, ask your doctor about taking over-the-counter medications such as ibuprofen (Advil) or acetaminophen (Tylenol).

Ways to eliminate pain and discomfort in the hand:

• Cover the affected area with a cool, clean, damp cloth.
• Stretch your arm or do exercises with that arm.

In most cases, discomfort from heat or pain is normal. Contact your doctor if:

• If redness and pain at the injection site increases after 24 hours.
• If side effects bother you greatly or do not go away after a few days.

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Why isn’t every pain after an injection a side effect?

Short. Not everything that happens after vaccination is a result of the vaccine.

Like all medicines and medical procedures, vaccines can have unwanted effects. This is quite expected: the entry of a new antigen from a vaccine into the body should cause an immune reaction - and not always a pleasant one. For example, in the form of interferon syndrome, which manifests itself in fever, aches, headaches, etc. (by the way, if over-the-counter “immunostimulants” worked, taking them would give exactly such sensations).

For example, quite often people complain of pain at the injection site. But since an injection is still a microtrauma, pain at the injection site is completely expected even when vaccinated with a “pacifier”. In the case of a real vaccine, the immune reaction (more precisely, the release of pro-inflammatory substances) can aggravate pain. Moreover, the severity of such a reaction will depend on the characteristics of the vaccine: the presence of an adjuvant, dosage, etc.

To establish which of these pains is a “side” of the vaccine, it is not enough to simply record the fact of unpleasant sensations. It is necessary to conduct a statistical study: compare the frequency of reactions in vaccinated people and the placebo group or the average population, and check the possibility of random differences. The same, generally speaking, is true for other, less obvious adverse reactions: headache (which can most likely occur both after vaccination and without it), weakness, high fever, and so on - even death.

Unfortunately, there are only two reliable ways to distinguish “real side effects” (those that occur precisely because of vaccination) from reactions that are not (those that occur after vaccination, but not as a result of it). This:

• statistical analysis of the frequency of these events in the vaccinated and control groups;
• a detailed analysis of a specific medical history of a specific person, in which it is possible to establish cause-and-effect relationships between the vaccine and the consequences.

How are data on adverse reactions collected?

Short. The most reliable way to look for adverse reactions is in phase III clinical trials, where people are randomly assigned to receive a vaccine or a placebo. Medical services in different countries look for rare side effects after vaccination, receiving reports from vaccinated people.

Phase III clinical trials usually become a source of information about the main, most common side effects. If in the vaccinated group any adverse reactions occur significantly more often than in the placebo group, then this is reliable evidence that vaccination is the cause of these phenomena.

Randomization produces the most reliable data—but such studies have an important drawback. They involve thousands or at most tens of thousands of volunteers, which means it is impossible to guarantee that they will detect very rare adverse reactions that occur once every hundred thousand vaccinations. These rare reactions can be quite serious and attract a lot of attention, so even though they are rare, they need to be monitored.

To find them, the pharmacovigilance system is used - a set of mechanisms by which medical services collect information about side effects after vaccinations. The better pharmacovigilance works in different countries, the more adverse reactions will be detected even in very similar or identical vaccines. If rare adverse reactions for a vaccine have not been recorded in a country, this does not mean that they do not exist - perhaps the system is simply not able to detect them. That is why, for an objective analysis of side effects, it is important to compare data obtained from different countries, even if using different methods.

Another way to identify adverse reactions is observational studies, in which there is no randomization, there are no large groups of vaccinated people as in post-registration studies, but instead all trial participants are carefully examined or interviewed.

What are the possible side effects?

Short. Serious “side effects” are not the same as severe. Serious ones threaten with dangerous illness and death, severe ones simply interfere with normal life. Reactions can be local or systemic (which affect the entire body). And also rare, frequent and very frequent (in 10% of vaccinated people or more).

It is important to understand that when the news talks about “severe” side effects, this does not always mean that the vaccine led to a dangerous disease or, moreover, was life-threatening. Any adverse reaction during vaccination may have varying degrees of severity. According to the FDA and EMA classification, all reactions have five levels of severity:

• mild (mild, grade 1) - everything that does not interfere with everyday life and goes away on its own;
• moderate (moderate, grade 2) - this includes reactions such as short-term high fever and bouts of nausea;
• severe (severe, grade 3) - something that greatly interferes with living and working or requires the use of medications;
• requiring intervention (grade 4) - a reaction that requires medical assistance (which, however, does not always end in hospitalization);
• fatal outcome (grade 5).

Serious side effects are not the same as severe. Only grade 4 and grade 5 reactions are considered serious, that is, those that threaten dangerous illness and death. A headache, for example, may interfere with work and would be considered a severe reaction (grade 3), but would not be classified as serious because it does not pose a major health risk.

Undesirable reactions are also divided into local (such as redness at the injection site) and systemic (such as fever). The terms “common”, “rare”, “very frequent”, etc. have a clear numerical expression: thus, “very frequent” are all reactions that are observed in 10% of vaccinated people or more.

And if a person has no “side effects” at all, does that mean the vaccine didn’t work?

Short. No, that doesn't mean it.

If after vaccination there is no headache, no body aches, no fever, this does not mean that the immune response is weak or absent, and the body is defenseless against the disease. Why some people feel this reaction and others do not, and whether there is a correlation between the brightness of the “side effects” and the “strength of immunity” is an interesting, but separate question, there is no clear answer to it.

If this is enough for you to get vaccinated, here are our instructions

Finally decided to get vaccinated? Hooray! Here's how to prepare—and how to get a vaccine that actually works.

3 months ago
If this is enough for you to get vaccinated, here are our instructions

Finally decided to get vaccinated? Hooray! Here's how to prepare—and how to get a vaccine that actually works.

3 months ago
Part 2 (which you've been waiting for)

Is there any way I can prevent or reduce side effects from the vaccine?

You should wait until you get vaccinated and then monitor how you feel. If side effects occur, you can take over-the-counter medications (such as Advil or Tylenol) to lower your fever, reduce chills, or relieve headaches or body aches. It is vital that you do not take these medications before getting a vaccine, as there are theoretical concerns that some pain medications may interfere with the immune response to the vaccine. It is also unclear whether taking medications ahead of time actually helps reduce symptoms after vaccination.

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What should I do if swelling or pain occurs at a location other than the vaccination site?

Some patients may experience some enlargement or tenderness of their lymph nodes after receiving the Pfizer-BioNTech or Moderna vaccines. In addition, enlarged lymph nodes may be detected on medical imaging and may be mistaken for progression of some types of cancer—most notably breast cancer, head and neck cancer, melanoma, and lymphoma.

This vaccine side effect is more common after the second dose. It usually occurs within 2–4 days after vaccination and can last an average of 10 days.

Enlarged lymph nodes may be visible for a longer period of time on imaging. Therefore, our recommendations will be as follows:

• If you experience these symptoms after vaccination, you should contact your doctor. In most cases, it is recommended to wait at least four weeks before undergoing further testing to allow the lymph nodes to shrink to normal size during this time.
• COVID-19 vaccination should be administered after routine medical imaging procedures. If you have already received the vaccine, we recommend that you have routine breast screenings, including mammograms and MRIs, no sooner than six weeks later.
• If you are a cancer survivor, you should ask to receive the COVID-19 vaccine, if possible, on the opposite side that was not affected by the cancer.
• If enlarged nodes cause you discomfort, you can apply a warm compress. You can take acetaminophen or nonsteroidal anti-inflammatory drugs to relieve discomfort.

It is important to know that all types of vaccines can cause temporary enlargement of lymph nodes. This may indicate that the body is producing antibodies, as it should be.

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Vaccination calendar

Contraindications for vaccination are: severe reaction to previous vaccine administration, current acute diseases, malignant disease or the presence of immunodeficiency, severe chronic diseases in the acute stage.

Some vaccinations require revaccination - repeated administration of the vaccine to consolidate acquired immunity. This procedure should not be avoided; it will help the baby better resist diseases.

Immunity develops some time after vaccination.

Clinical studies show that vaccination may provide some protection about 12 days after the first dose, but you must receive both doses for full protection. After both doses are administered, the vaccine is more than 90% effective at preventing COVID-19 infection.

On May 13, the Centers for Disease Control and Prevention (CDC) announced that people who have completed a full course of vaccination may no longer wear a mask or practice social distancing in most cases. However, the CDC also noted that people with weakened immune systems, such as cancer patients, should talk to their health care provider about the need for protective measures, even if they have been vaccinated. Therefore, to protect our patients from COVID-19, all employees, patients and visitors must continue to wear masks while at MSK. These requirements also apply to people who have completed the full course of vaccination.

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