Dangerous vaccines. What are the side effects and adverse events

Dangerous vaccines. What are the side effects and adverse events

A vaccine is a medical product. Vaccines, although designed to protect against disease, can cause side effects, just like any medicine.

Most side effects from vaccination are mild, such as pain, swelling, or redness at the injection site. Some vaccines are associated with fever, rash, and pain. Serious side effects are rare, but can include life-threatening seizures or allergic reactions.

A possible side effect resulting from a vaccine is known as an adverse event.

Every year, American babies (1 year and younger) receive more than 10 million vaccines. During the first year of life, a significant number of babies suffer serious and fatal illnesses and medical events, such as sudden infant death syndrome (SIDS). Also, it is during the first year that congenital conditions can become apparent. Therefore, due to chance, many babies will experience a medical event very close to a vaccine. However, this does not mean that the event is related to immunization. The challenge is determining when a medical event is directly related to a vaccine.

The Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) have established systems to monitor and analyze reported adverse events and to determine whether they are related to vaccination.

Types of side effects

To understand the range of possible side effect events from vaccination, it is helpful to compare a vaccine with relatively few associated side effects, such as the Haemophilus influenza type B vaccine, with a vaccine that is known to have many potential side effects, such as infrequently they used the smallpox vaccine (given to military personnel and others who may be the first responders in the event of a bioterrorist attack).

Haemophilus influenza type B is a bacteria that can cause serious infections, including meningitis, pneumonia, epiglottitis, and sepsis. The CDC recommends that children receive a series of Hib vaccines beginning when they are two months old.

Smallpox is a serious infection, fatal in 30% to 40% of cases, and caused by the Variola major or Variola minor virus. There have been no reports of wild pox since the 1970s. The World Health Organization has declared it eradicated.

The information below on the side effects of vaccination against Hib and smallpox comes from the Centers for Disease Control and Prevention.

Side effects of the Hib vaccine

Redness, warmth, or swelling at the injection site (up to 1 in 4 children)
Fever over 101 ° F (up to 1 in 20 children)

No serious side effects have been associated with the Hib vaccine.

Side Effects of Smallpox Vaccine (Vaccinia)Mild to moderate problems

Mild rash, lasting 2 to 4 days.
Swelling and tenderness of the lymph nodes, lasting 2 to 4 weeks after the blister has healed.
Fever over 100 ° F (about 70% of children, 17% of adults) or over 102 ° F (about 15% -20% of children, less than 2% of adults).
Secondary blister anywhere on the body (about 1 in 1,900).

Moderate to severe problems

Serious eye infection or loss of vision due to the spread of the vaccine virus to the eye.
Rash all over the body (up to 1 in 4,000).
Severe rash in people with eczema (up to 1 in 26,000).
Encephalitis (severe brain reaction), which can lead to permanent brain damage (up to 1 in 83,000).
Serious infection that begins at the vaccination site (up to 1 in 667,000, mostly in people with weakened immune systems).
Death (1-2 per million, mainly in people with weakened immune systems).

For every million people vaccinated against smallpox, between 14 and 52 could have a life-threatening reaction to the smallpox vaccine.

How do I find out the side effects for different vaccines?

When you or a child receives a vaccine, the healthcare provider gives you a brochure known as the Vaccine Information Statement (VIS). The VIS describes common and rare side effects, if any, of the vaccine. Your healthcare provider will likely discuss possible side effects with you. VIS downloads are also available through the CDC website.

Package inserts produced by the vaccine manufacturer also provide information on adverse events. Furthermore, these inserts generally show adverse event rates in the experimental and control groups during pre-market vaccine trials.


The CDC and FDA established the Vaccine Adverse Event Reporting System in 1990. The goal of VAERS, according to the CDC, is "to detect possible signs of adverse events associated with vaccines." (A signal in this case is evidence of a possible adverse event that emerges in the collected data). About 30,000 events are reported each year to VAERS. Between 10% and 15% of these reports describe serious medical events that result in hospitalization, life-threatening illness, disability, or death.

VAERS is a voluntary reporting system. Anyone, such as a parent, healthcare provider, or friend of the patient, who suspects an association between a vaccination and an adverse event can report that event and the information to VAERS. The CDC then investigates the event and tries to find out if the adverse event was in fact caused by the vaccination.

The CDC states that they monitor VAERS data at

Detect adverse events from new, unusual, or rare vaccines
Monitor increases in known adverse events
Identify possible patient risk factors for particular types of adverse events
Identify lots of vaccines with a higher number or types of reported adverse events
Evaluate the safety of new licensed vaccines

Not all adverse events reported to VAERS are caused by a vaccine. The two occurrences can be related only to time. And, it is likely that not all adverse events resulting from vaccination will be reported to VAERS. The CDC indicates that many adverse events, such as swelling at the injection site, are not reported. Serious adverse events, according to the CDC, "are probably more likely to be reported than minor ones, especially when they occur shortly after vaccination, even if they may be a coincidence and are related to other causes."

VAERS has successfully identified several rare adverse events related to vaccination. Among them are

An intestinal problem after the introduction of the first rotavirus vaccine (the vaccine was withdrawn in 1999)
Neurological and gastrointestinal diseases related to the yellow fever vaccine

Additionally, according to Plotkin et al., VAERS identified the need for further investigation of the association of MMR with a blood clotting disorder, encephalopathy after MMR, and syncope after immunization (Plotkin SA et al., Vaccines, 5th ed. Philadelphia: Saunders, 2008).

Datalink Vaccine Safety

The CDC established this system in 1990. The VSD is a collection of linked databases that contain information from large medical groups. Linked databases allow officials to collect data on vaccination among populations served by medical groups. Researchers can access the data by submitting studies to the CDC and having them approved.

The VSD has a few drawbacks. For example, few fully vaccinated children are listed in the database. Medical groups that provide information to VSDs may have patient populations that are not representative of large general populations. Also, the data does not come from randomized, controlled, and blinded trials, but from actual medical practice. Therefore, it can be difficult to monitor and evaluate the data.

Rapid Cycle Analysis is a VSD program, launched in 2005. It monitors real-time data to compare adverse event rates in recently vaccinated people with rates among unvaccinated people. The system is used primarily to monitor new vaccines. Among the new vaccines that are monitored in the Rapid Cycle Test are the meningococcal conjugate vaccine, the rotavirus vaccine, the MMRV vaccine, the Tdap vaccine, and the HPV vaccine. Possible associations between adverse events and vaccination are studied further.

Original article (in English)

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