Vaccine against whooping cough: the answers to the most frequent doubts

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In this article

• Doubts about vaccination
• How vaccination works in Del Paese
• Effectiveness of the vaccine
• Duration of immunity
• Mutations of the bacterium and vaccine efficacy
• Herd immunity
• Vaccine and transmission of infection
• How to protect newborns and infants from whooping cough
• Conclusions

Vaccine yes or vaccine no?

There is a lot of discussion on the web about the usefulness of the pertussis vaccine. Mothers and fathers ask themselves, sometimes also referring to some data from the scientific literature, if vaccination really works, how effective it is and how important it is in the case of this disease, the effect of herd immunity, that is, the fact that, beyond above a certain threshold of vaccinated in a population, even those who have not been vaccinated are protected.

So many doubts, in short, which we try to clarify taking into account the indications of the official Position paper of the World Health Organization on pertussis vaccines (released in August 2022), and with the help of Paolo Bonanni, professor of hygiene at the University of the city and member of the working group on vaccines of the Del Paesena Hygiene Society.

How vaccination works in Del Paese

The pertussis vaccine exists only in combined form, with that for tetanus and diphtheria (DPTa). There are two formulations: one pediatric, indicated up to six years, and one for adults, used after seven years, generally for boosters. For the infant, the DPTa vaccination is contained in the hexavalent vaccine, which, as the name implies, protects against six diseases in all (pertussis, diphtheria, tetanus, polio, hepatitis B and Haemophilus influenzae type B infections).

The current vaccination schedule includes three doses of DTPa (with hexavalent) respectively at three months, five months and between 11 and 13 months of life. They are also expected two recalls in pediatric age with DTPa alone (possibly associated with polio vaccine) at six years and at 14 years. Finally, in adults a recall for diphtheria-tetanus-pertussis every 10 years.

Pediatric vaccination against pertussis is one of the ten mandatory vaccinations in our country. Furthermore, vaccination against pertussis is - together with the flu vaccination - recommended and offered free of charge to pregnant women. 

Read also: Vaccines for childbearing age and pregnancy: the new recommendations of the Ministry of Health

How the pertussis vaccine is made

The whooping cough vaccine is a acellular vaccine: it means that it does not contain the whole organism (the Bordetella pertussis bacterium), although inactivated, but only some of its protein components. In some countries, including the Del Paese, the acellular vaccine has replaced the cellular vaccine (whole, inactivated) over the years because the latter, although safe, tends to give some more side effects.

How effective is the pertussis vaccine?

Is it possible for a child to get sick even after getting vaccinated against whooping cough?

To answer this question it is worth making a premise: unlike what happens with other diseases, such as measles which, except in very rare cases, tends to confer permanent immunity, whooping cough can get you sick several times in your life. Likewise, pertussis vaccination is not "eternal", but confers an immunity that tends to fade over time and for this reason periodic recalls are foreseen.

That said, it is estimated that the efficacy of the acellular vaccine for pertussis is around 85%: it means that the vast majority of vaccinated children are effectively protected against the disease (unless the calls are skipped ...). Of course, it may be that in some children the vaccine does not work or works poorly, and that therefore this child can get sick, but it happens rarely. "And in any case, the fact that the vaccine doesn't always work perfectly is not a good reason not to: better to have perhaps imperfect protection than not to have it at all"comments Paolo Bonanni.

How long does the immunity conferred by the vaccine last?

Some studies suggest that the immunity conferred by the pertussis vaccine wears off very quickly. Therefore, there are those who wonder if under these conditions it is still worth vaccinating. Indeed, there are studies that indicate a rather short "duration" (two to four years) of immunity conferred by the DTPa vaccine, at least in adolescents. In reality, as stated in the WHO Position paper, "the precise rate of decline in vaccine efficacy, and the mechanisms involved in this decline, are not well understood", and different studies report different "durations". "Other investigations give less negative results, with protection periods of around five years or more "declares Bonanni.

For sure, according to the WHO document the decline in vaccine efficacy is one of the factors contributing to the return of whooping cough in some countries of the world. Again, however: this does not mean that vaccination is useless, it is a protective tool nonetheless. "At best, this type of observation should lead to the request for more vaccinations, not less vaccinations" Bonanni underlines.

Mutations of the bacterium and vaccine efficacy

Some studies indicate that the Bordetella pertussis bacterium, responsible for the disease, is mutating and that these mutations lead it to lose the very proteins against which the vaccine is directed. Does this mean that the vaccine will soon no longer work? Actually at the moment the alarm does not seem justified.

The WHO Position paper clearly states: "In the regions where the acellular vaccine is used, mutant bacterial strains have been isolated that lack one of the proteins against which the vaccine is directed, in particular the PRN protein. theory, this could compromise the vaccine's effectiveness, but in practice, a significant reduction in efficacy has never been observed caused by changes in the genetic characteristics of the bacterium ". And again:"There is currently no evidence of a reduced efficacy of the vaccine even in the presence of different Bordetella pertussis strains.".

Moreover, the vaccine is constructed in such a way as to target more proteins of the bacterium: "Even if one is missing, there are still others to attack" explains Bonanni. "It may be that in some contexts the vaccine is a little less effective but, as always, it is still better than nothing." Moreover, it should not be forgotten that research is always at work: once the problem (mutant bacterial strains) has been identified, the researchers are trying to develop new solutions, that is, new vaccines.

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Does herd immunity to whooping cough work or not?

According to what emerges from some FAQ (Frequently Asked Questionts) of the Centers for Desease Control in Atlanta, probably the effect of herd immunity may be less relevant in the case of whooping cough than it is for other diseases, such as measles. This for various reasons including:

• high contagiousness of the disease, which spreads very easily;
• decrease in the effectiveness of vaccination over time;
• possible limited ability of vaccination to prevent transmission of infection from one infected individual (but protected by vaccination) to other susceptible individuals.

"But even these are not good reasons to choose not to vaccinate. On the contrary, it is an invitation to don't get left behind with the lures"Bonanni comments." First of all, because vaccination is in any case the most effective tool we have to protect individuals from whooping cough. And remember that under the age of five it is a disease that can have important complications. And secondly because, in limited environments, herd immunity, even if not perfect, can still work ".

It is no coincidence that a strategy called cocooning has been proposed to protect newborns and infants not yet vaccinated, which provides for the immunization of all people in close contact with children, to reduce the risk of them becoming ill.

Can the vaccine prevent the infection from being passed on to others?

Whether in addition to preventing the onset of the disease in the vaccinated person, the vaccine is also effective in blocking the transmission of the infection to others is currently being studied. Some mathematical models and research done on baboons actually suggest that the acellular vaccine fails to block the transmission of whooping cough to others. Or: those who get vaccinated do not get sick in the event of Bordetella pertussis infection, but they can probably also transmit the infection to others.

We do not yet know exactly what happens in the case of man, although it is plausible that the same happens. Some scholars believe that this feature of the acellular vaccine is one of the causes of the return of whooping cough that is being witnessed in some countries.

In the case of the cellular vaccine (which contains the whole bacterium, in an inactivated form) the problem does not seem to exist. As we said, however, many countries have abandoned the cellular vaccine because it is more reactogenic.

How to protect newborns and infants from whooping cough

The strategies proposed by the Global Pertussis Initiative, an international group of experts on the subject, and also taken up by the Position paper of the World Health Organization, are two: vaccination of expectant mothers in the last trimester of pregnancy and cocooning.

• Vaccination of mothers with acellular vaccine in the last trimester of pregnancy. Available data indicate that this strategy is safe and highly effective in protecting newborns, at least until such time as they can be vaccinated themselves. This strategy is also recommended by our Ministry of Health. 
• The cocooning strategy, or cocooning, also this already implemented in some countries (Australia, France, Germany, United States, Chile, Costa Rica), consists in the vaccination (or revaccination), preferably in the months preceding the birth, of all the people who will come into close contact with the newborn (parents, grandparents, siblings, other close family members, any babysitters). Since this strategy can have an impact on the prevention of the disease only in particular circumstances (if implemented in the right time and really "on the carpet") and in any case has quite high costs, Global Pertussis Initiative and WHO identify in the vaccination of pregnant mothers is the most effective defense strategy.

Conclusions

The vaccine for whooping cough has some critical issues, in part related to the characteristics of the disease itself. However, these criticalities are not sufficient to justify a renunciation of vaccination.

As the main national and international scientific authorities (from the WHO to the Centers for Disease Control in Atlanta) underline, vaccination for whooping cough remains the most effective tool we have to protect ourselves from this disease. And, with the appropriate precautions, also to protect the little ones, who take the worst risks. Unfortunately, including death.

Questions and answers

How long does the coverage of the pertussis vaccine last?

It is not yet clear how long exactly it lasts. Some studies suggest that it fades fairly quickly, others that it guarantees protection for periods of around five years. We know for sure that the coverage does not last a lifetime, which is why periodic reminders are provided even in adulthood. 

Is the pertussis vaccine dangerous in pregnancy?

The pertussis vaccine is not only considered safe in pregnancy, but is currently recommended by various international and national health authorities. In Del Paese, the pertussis vaccine is recommended by the Ministry of Health for pregnant women (in the third trimester).

TAG:

• whooping cough
• vaccinations for children
• pertussis vaccination
• herd immunity