Immunization Frequently Asked Questions (FAQs)

• Won't breastfeeding and good nutrition prevent these childhood infections?
• Aren't the only children who die of these infections suffering from malnutrition or defects of the immune system?
• Do vaccines really work?
• Is there a risk of catching the illness from the vaccine itself?
• Why do some children who have been vaccinated still get measles?
• If the first dose of measles vaccine doesn't work, won't a second dose also fail?
• How can immunity that results from immunization be a good as immunity from natural infection?
• Does immunity wear off over time?
• Won't adults be a risk of catching these infections if immunity wears off?
• Are some boosters necessary?
• Keep vaccinations up-to-date

Won't breastfeeding and good nutrition prevent these childhood infections

Breastfeeding is not an alternative to infant vaccination. Breastfeeding provides some good protection against many infections because special antibodies are made in the breast and are present in human breast milk. Babies who are breastfeed generally have lower rates of many infections, including viral respiratory infections, ear infections and diarrhea. The protection provided by breast milk is incomplete and can be overcome if the baby is exposed to a large amount of a germ. Moreover, the protection disappears rapidly as soon as breastfeeding stops.

Good nutrition helps the body's defences against infection to function normally. Infections are more severe in anyone with poor nutrition. Special immune cells called lymphocytes are easily damaged if one's diet does not include enough protein. For this reason, malnourished children are much more likely to die of infections such as measles or pertussis than well-nourished children. Vitamin A deficiency, in particular, greatly increases the risk of severe illness.

Aren't the only children who die of these infections suffering from malnutrition or defects of the immune system?

Although infections such as measles and pertussis are much more likely to kill a child who is malnourished or who has immune system defects, these infections can also kill healthy, well-nourished children. Malnutrition was not a contributing factor in the deaths of any of the children who died of pertussis in the United States in the 1990s.

Do vaccines really work?

Yes!

All vaccine-preventable diseases have declined significantly in countries with successful immunization programs. Wherever vaccination rates are high, disease rates are low. Conversely, when vaccination rates decline (often because of fear of unproven dangers of vaccines), the diseases and related deaths increase in frequency.

Smallpox was the first disease to disappear because of vaccination. There have been no cases of smallpox anywhere in the world since 1979!

Paralytic polio has been eliminated from most of the world by vaccination. A global vaccination program is expected to completely eradicate the disease within the next 5 years.

Is there a risk of catching the illness from the vaccine itself?

Inactivated vaccines (such as inactivated polio and influenza vaccines) and purified vaccines (such as diphtheria and tetanus toxoids, and Hib, acellular pertussis, pneumococcal, meningococcal, hepatitis A and HPV vaccines) do not have any living germs in them. These vaccines stimulate the immune system, but they cannot cause the infection.

Live Attenuated vaccines (such as measles, mumps, rubella and chickenpox vaccines) do infect cells and multiply in the body. The vaccine viruses have been sufficiently weakened (attenuated) in the laboratory that they stimulate immunity without causing a full-blown infection. Measles, mumps and rubella vaccine viruses do not spread from a vaccinated child to another person. Chickenpox vaccine is also a live, attenuated vaccine. Spread of this vaccine virus may occur after vaccination of healthy children, but such spread is extremely rare. However, the vaccine virus can sometimes spread from a vaccinated child who has leukemia to other children.

Oral polio vaccine (OPV), however, not only infects the intestinal tract, but is also excreted in the fees. The vaccine strains can spread from person to person ( for example, but touching a feces-contaminated surface or object). Such spread is usually helpful, though, because those who get the polio vaccine virus this way may also become immunized.

OPV is a very safe and effective vaccine. There is, however, an extremely small risk of getting paralytic polio from the vaccine. The risk of vaccine -associated paralytic polio is estimated to be 1 case in 750,000 first doses of vaccine and 1 case in 6.9 million subsequent doses. The risk for those in very close contact with an infant vaccinated with OPV is 1 case in over 20 million doses of vaccine.

To avoid the very small risk of disease associated with the oral vaccine, Canadian provinces and Territories that did use the live OPV switched to the inactivated polio vaccine (IPV) during the 1990s. Since 1997, only IPV has been used in Canada. Experts are confident that the switch to IPV will maintain the remarkable accomplishment of eradication of paralytic polio in the Western Hemisphere.

Why do some children who have been vaccinated still get measles?

Opponents of vaccination are quick to point out that many cases of measles occur in vaccinated children. They claim this proves that the vaccine doesn't work. In outbreaks of measles in Canada and the United States in the 1990s, it is true that more than half of the cases occurred in school-age children who had been given measles vaccine. But to say that this means that vaccine doesn't work is incorrect. This argument is too simplistic, and it uses faulty logic.

We know that 1 dose of measles vaccine is not 100% effective. We know that about 5- 10% of children are not protected after a single dose of vaccine. Let's use these facts in an example.

Example

In a school with 1,000 students, assume 95% of children get vaccinated. This means that there are 950 vaccinated children and 50 unvaccinated children. The number of children who are still susceptible to measles is 145- 50 unvaccinated children who are unprotected after 1 dose (of 95).

One child in the school comes back from a holiday with measles. Measles is so contagious that is quickly spreads in the school. One-half of the 145 susceptible children catch it: half of the 50 unvaccinated children (or 25) get measles and half of the 95 vaccine failure children (47) get measles. Therefore, there are 72 cases of measles.

The proportion of cases that occurred in vaccinated children is 47 of the total 72, or 65%! This seems very high, but it does not mean that the vaccine works only 65% of the time.

Whenever a vaccine is not 100% effective and most children have been vaccinated, more cases will in vaccinated than in unvaccinated children during outbreaks, only because more vaccinated than unvaccinated children.

The 25 cases of measles in the unvaccinated group came from a total 50 children: the attack rate in this group is 50%. The 47 cases among vaccine failures came from a total of 950 children, an attack rate of only 4.9%.

From these numbers, we can see that unvaccinated children were 10 times more likely to catch measles! The vaccine was 90% effective. This is the commonly observed figure when only 1 dose of measles vaccine is given. When 2 doses are routinely given to children, the vaccine is nearly 100% effective and outbreaks no longer occur among vaccinated children.

If the first dose of measles vaccine doesn't work, won't a second dose also fail?

The main reason infants fail to respond to measles vaccine is the presence of antibody to measles, which infants get from their mothers during pregnancy. It takes only a very small amount of antibody to kill the measles vaccine virus. (If the immune system kills the vaccine virus, the vaccine will not induce immunity to natural measles virus.) About 5% of infants still have enough measles antibody at the 12 months of age to do just that.

Studies of children who failed to respond to the first dose of vaccine at 12 to 15 months of age have shown that over 99% of them did respond normally to the second dose. Studies of outbreaks in schools have confirmed that measles is very rare in children who have 2 doses of measles vaccine.

How can immunity that results from immunization be a good as immunity from natural infection?

Opponents of vaccination often claim that natural immunity (from an infection) is better than immunity from a vaccine. Immunity after most vaccines is just as effective as that induced by disease. As, well, very infection described in this book has a great risk of causing harm. The truth is that the proven risk of damage and death caused by the disease is far worse than the so-called "benefit" of obtaining immunity trough disease.

To understand that the two ways of achieving immunity are equally effective, you must first understand how the immune system works. An overview is presented below.

How the immune system works

There are two functions of the immune system: immediate response and the long-term response. The immediate response kills infections germs and promotes recovery from the infection. The long-term response maintains immunity so that the person will be protected against infection if exposed to the germs in the future.

Immediate response

The parts of the immune system involved in destroying bad germs are called antibodies and lymphocytes. Antibodies are proteins made by immune cells. The antibodies attach to the surface of the germ and kill it, either by damaging it directly or by allowing other white blood cells to kill the germ. Lymphocytes (white blood cells) can attack some germs directly. Usually, through, lymphocytes work indirectly by killing the cells that are infected with the germ.

It takes time for the body to develop an immediate immune system response. So, with natural infection, sometimes the infection kills the person or causes severe damage before the immune response kicks in.

Vaccines are used to stimulate both antibodies and lymphocytes so that they are present in the body before exposure to an infection occurs. Following vaccination, the immune system responds as if infection has occurred. There may be a difference in the amount of antibody made after infection compared with after vaccine, but the same kinds of antibodies and immune cells are made. The antibodies and the lymphocytes produced in both cases target the identical chemicals on the surface of the germ.

Long-term response

The second function of the immune system is to establish immune memory. When we say a person is immune to a certain disease, we mean that immune memory against that particular infection has been established. Special lymphocytes, called memory cells, are stimulated by both infection and vaccination. These memory cells live (remain active) for a very long time, perhaps even for life. If a person with established immunity to a certain infection is exposed to that infection again, the active memory cells respond very quickly and signal both the cells that make antibodies and the cells that attack germs to get to work.

It is important to note, however, that each type of infectious germs is attacked by a separate, distinct set of antibodies and lymphocytes. Immunity to one infection does not "create" immunity to other infections. Antibodies and lymphocytes made in response to measles infection or measles vaccine react only to measles virus. Memory cells for rubella infection will not activate antibody to fight against diphtheria.

In summary, immunity induced by vaccines is as effective as immunity induced by disease, without the risk of disease.

Does immunity wear off over time?

The levels of antibody in the blood decline over time following both natural infection and vaccination. But even though antibodies disappear, immune memory persists. Most vaccines produce immune memory that lasts a very long time, if not for life.

But others, for example diphtheria and tetanus toxoids and pertussis vaccine, must be repeated to maintain protection against diphtheria, tetanus and pertussis. These repeated shots are called boosters. When a booster is given to a person who already has immune memory (perhaps from a previous booster), the immune response creates antibody (necessary to fight infection) much faster and stronger than when a booster is given to a person with no immune memory.

In other words, the process of building immunity takes longer in a person who has never been exposed to the infection before. In the time it takes this person's immune system to build immunity against a particular germ, that germ can do lots of damage.

Won't adults be a risk of catching these infections if immunity wears off?

Infections such as measles, mumps rubella and chickenpox are more severe in adults than in children. Therefore, there is some concern that adults might be a risk if immunity from childhood vaccination wears off. Natural infections with measles and rubella do induce lifelong immunity. While recent outbreaks of measles and mumps in the United Kingdom were the result of lack of vaccination, an outbreak of mumps among college students in the United States in 2006 seemed to be the result of warning immunity over time.

Vaccination also produces very long-lasting immunity. Immune memory resulting from vaccination seems to persist even if there is no antibody detectable in the blood. The occurrence rate of measles, rubella and chickenpox among those who were the first to be vaccinated has not been affected by the passage of time. Immunity induced by mumps vaccine may wane after 15-20 years, as noted above.

The medical surveillance system in Canada maintains as watch on the occurrence of many infectious diseases (see chapter 2). This complex reporting network detects changes in the frequency of infections occurring in the North American population. If infections are beginning to occur in adults who were vaccinated as children, the network will respond by adjusting the vaccination program appropriately (e.g., adding booster doses of vaccine).

Are some boosters necessary?

Although diphtheria and tetanus are also severe diseases in adults, they are somewhat different from most other infections in the way they cause disease. Both of these diseases cause illness by producing a toxin (or poison). Protection against these diseases requires the actual presence of antibody in the blood at the time a person is exposed to the toxin.

Even though immune memory lasts 40 years or more after vaccination, antibody levels decrease over time. These infectious toxins are so potent that disease can occur before the immune system has time to respond. Adults must receive boosters every 10 years to be protected against diphtheria and tetanus. They shouldn't wait until there is a need.

The diseases caused by tetanus toxin do not induce immunity: the toxin produced by the tetanus germs is so potent that tiny amounts cause disease without stimulating an immune response. Those who get tetanus still need to be immunized and have boosters.

Keep vaccinations up-to-date

After vaccination, patients are given a card to record the date and vaccine received. These cards are a record of vaccination and should be kept-up-date, in a safe place.

 Your Child's Best Shot, A parent's guide to vaccination, 3rd edition by Ronald Gold, MD, MPH