The vaccine given today against whooping cough is losing its effectiveness and the doctors are racing to protect the children
In the late summer of 2010, the number of children in California who contracted whooping cough rose to an alarming rate: five times the number of patients in the first half of 2009. David Witt, a physician and infectious disease specialist working at the Kaiser Permanente Medical Center in San Rafael, treated some of the sick children. His clinic is located in the heart of Marin County, a stronghold of the counterculture that sits on the northern tip of the city of San Francisco. At first he assumed that the outbreak of the disease was the result of parents refusing to vaccinate their children. But as the number of cases continued to rise each month, not just in Northern California but across the country, Witt began to wonder if something else had gone wrong.
With the help of his son Maxwell, who was a college student at the time, and his colleague pediatrician Paul Katz, Witt examined the records of 132 patients who were covered by Kaiser Permanente's medical insurance, who had not yet turned 18 and who were diagnosed with the pertussis bacterium between March and October 2010.
"Most of the cases were discovered in children aged 8 to 12 years who received a full vaccination," says Witt. "It was a complete surprise." The conclusion that emerged from Witt's small study, and which was later confirmed in larger studies, is that the protection afforded by the vaccine, which has been in use for twenty years, is fading faster than the health authorities anticipated. The pertussis rate at least tripled between 2011 and 2012 in 21 countries. Some of the cases occurred in children who had never been vaccinated, but most of the sick children were vaccinated, and the vaccine failed to protect them over time.
Now, the health authorities are in a hurry to plan new strategies to protect the children, and there are no easy solutions. No one is currently engaged in developing a better component to replace the current component. A recommendation to increase the number of injections of the current vaccine will only provoke public debates that will last for years, and it is not clear whether these booster vaccines will actually help. Even discussing the issue causes discomfort: at a time when anti-vaccination sentiment is so strong, and at a time when childhood refusal rates have reached record highs, no one wants to question the effectiveness of one of the key tools of public health.
Side Effects
Before the pertussis vaccine was available in the 40s, many parents learned firsthand that pertussis was a terrible disease. The bacteria that causes it, Bordetella pertussis, produces a toxin that damages the tiny hairs that line the walls of the lungs, preventing them from clearing mucus and invading bacteria from the airways. The children suffer from uncontrollable coughing fits that give the disease its name, followed by wheezing and suffocation. The coughs can be so strong as to cause convulsions and brain damage. Before the vaccine era, pertussis affected about 200,000 children in the US each year and killed about 8,000. The new vaccine reduced disease rates from 157 cases per 100,000 people to 100,000 case per XNUMX.
However, success had a price. At the time, the researchers developed the first pertussis component from killed pertussis bacteria that could not reproduce but contained many bacterial proteins that the immune system learned to recognize. This way the immune system was able to attack the pertussis bacteria before they caused the disease. Unfortunately, these components, which were based on whole cells, also contained other molecular components that could cause unwanted reactions of the immune system, such as swelling at the injection site, and in rare cases high fever that caused a dangerous inflammatory reaction in the brain. "In those days, people didn't pay attention to the side effects, because the mortality rate before the development of the compound was so shocking," says James Cherry, a professor of pediatrics and vaccine researcher at the David Geffen School of Medicine at the University of California, Los Angeles.
But in the following years, concerns increased due to the vaccine's side effects. In the 70s, Sweden and Japan stopped using the vaccine. A government study published in England in 1981 concluded that the vaccine causes irreversible brain damage once in 310,000 injections (a study whose results have since been called into question). And in 1982, a criticism aired by the NBC network about the compound aroused public opinion against it and ignited the anti-vaccination movement in the US.
The US and other countries have invested extensive efforts in developing a more successful formulation, focusing on "non-cellular" preparations that used isolated bacterial proteins rather than the entire bacterium to produce an immune response, an approach that reduces the risk of an inflammatory response. Researchers combined the new pertussis component with components against tetanus and diphtheria. The vaccine, known as DTaP, was available to doctors in 1992 (in Israel, DTaP is given as part of the quintet vaccine). In the US, children receive the vaccine at the ages of two, four and six months; once more between 15 and 18 months; And one last time between the ages of four and six, before the start of first grade.
From the beginning, the health authorities realized that the al-Tai compound might confer a shorter-term immunity than the problematic formulation that contained whole bacteria. For this reason, it was decided in 2005 to provide an additional boost to ensure that children are protected during puberty. Officials in the American authorities determined that the booster dose would be most effective if given at the ages of 11-12, but approved it for use in adults as well, and eventually also in pregnant women.
Defense failure
After a pertussis outbreak in California in 2010, there were additional outbreaks in 2012 in Wisconsin, Vermont, Washington and other states. Analysis of the outbreaks showed that the pattern of infection was always the same. Tom Clark, a doctor and pertussis expert at the US Centers for Disease Control and Prevention (CDC), describes it as "a clear step-like pattern that goes up by age: six, seven, eight, nine and ten years." If you go back a few years [to the years when they used a composition from a whole bacterium], the step pattern does not exist."
The step pattern indicates that the more time passes since the last pertussis shot, the more likely the children will develop pertussis after exposure to bacteria. Many of these children are young and therefore did not receive the booster dose, so the researchers hoped that once the children received the additional shots, the outbreaks would disappear. But recent data from the outbreak in Washington dashed hope: 13- and 14-year-old children fell ill with whooping cough even after receiving the booster dose. Other studies have shown that the ingredient behaves differently from the old, active ingredient: children who received even one dose of the old, full ingredient, when it was still on the market, were better protected against whooping cough than children who received only the new ingredient. (Of course, children vaccinated with the new formulation were still better protected than children who had never been vaccinated.)
Clark adds that the original study of the non-cellular component conducted in the 80s tested whether it provided protection, but not how long it protected. Some of the diseases against which there are non-cellular components, such as Hib meningitis (caused by the bacterium Haemophilus influenzae B), are dangerous for children only for a short period in the first years, so long-term immunization is not necessary. But today, immunologists have better research tools and a more nuanced understanding of how immunity is created and maintained. "Many of the operations that would be done today to develop a component have never been done with a pertussis component," says Clark.
"By and large, we need a more successful component," says Mark Sawyer, a professor of clinical pediatrics at the University of California, San Diego and chairman of a task force that works with the Advisory Committee on Immunization Practices (ACIP), which helps set federal immunization policy. "But ACIP can't just make it happen. This is up to the scientists who will investigate what will make the vaccine more successful, and that is up to the pharmaceutical companies."
Even if they develop a new component, it will be difficult to prove its superiority. Every developed country vaccinates its children against whooping cough, so there is no large unprotected population that can prove the value of the vaccine. And before manufacturers are encouraged to consider developing a new ingredient, policymakers will need to consider the unintended consequences of the move. For example, directing too much of the limited resources of the producers to one new component will cause a shortage of others. Another question is whether parents will agree to bring their children to receive additional shots.
ACIP has been investigating the problem for more than a year. The commission is operating in unfamiliar territory because this type of failure has never occurred in other components. In June 2012, the task force concluded that because of the short-term effect of the booster dose, adding more shots to the current vaccination schedule would not significantly lower disease rates. Because of this, the group advised the committee not to change the vaccination policy and not to add a second booster dose at the age of majority, but to increase the number of pregnant women who receive the booster dose in the first place. The CDC estimates that today only 6% of pregnant women receive the shot. However, newborn babies, who cannot be vaccinated, are the most vulnerable to the dangerous effects of whooping cough. Improving the immunity of the people closest to them is therefore the best way to prevent death from pertussis.
Given the limitations of the current formulation, Clark bluntly states that in the general population "there will be a lot of whooping cough." But he adds that even though the disease rates are increasing, the number of deaths is not increasing. When vaccinated children develop whooping cough, the symptoms are milder. So there is still value to the new ingredients for whooping cough because they reduce not only the risk of death and serious illness but also the treatment expenses, and needless to say the emotional trauma that accompanies the severe complications. Because of this, says Sawyer, the health authorities should encourage the youth and adults in the US who have not received the booster dose, whose rate reaches 90%, to come and get a shot to protect themselves and the most vulnerable populations among us. "We do need a new ingredient," he says, "but we have not yet exhausted the best of the ingredients we have."
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on the notebook
Marin McKenna is a journalist, blogger and author of two books about public health. He writes about infectious diseases, global health and food policy.
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The article was published with permission Scientific American Israel
