Whooping cough (pertussis)

Whooping cough is a stubborn, weeks-long affair for adults – and life-threatening for a newborn. Between those two sentences lies the reason why every pregnant woman in Austria has for years been recommended a vaccination that is not meant to protect her but her baby in its first weeks of life. This page explains how that works, when it is given and why the timing is defined so precisely.

Why whooping cough belongs in antenatal care

A newborn cannot protect itself. Its own primary immunisation against whooping cough begins only at the age of two months and is dependable at the earliest at around six months, after the third dose. It is precisely in this gap – from birth to about the fourth month of life – that whooping cough infections run the most severe course.

Babies in their first weeks often do not cough typically at all. Instead they stop breathing: apnoeas, turning blue, feeding poorly. The great majority of all hospital admissions for whooping cough and practically all deaths concern children under six months. That is not a historical figure but the current position – in countries with well-functioning vaccination programmes too.

These children are almost always infected by adults in their immediate surroundings, who themselves only have a stubborn cough and never think it might be whooping cough. In studies of the source of infection it was predominantly parents, siblings and grandparents.

Two strategies follow from this constellation, and they complement each other: vaccinating the pregnant woman so that the baby comes into the world with protection of its own, and vaccinating those around it so that it is not infected in the first place.

How the vaccination works in pregnancy

The mechanism is remarkably simple. If a pregnant woman is vaccinated, she forms antibodies. From about the 30th week of pregnancy these antibodies pass in large quantities across the placenta to the baby – actively, against the concentration gradient, through the placenta’s own transport mechanisms. So the baby is born not with a residual amount but with an antibody level that can exceed the mother’s.

This borrowed protection lasts some months and thereby bridges exactly the gap until the baby’s own primary immunisation. Afterwards it wanes – which is why the baby’s own vaccinations remain necessary.

How well this works is unusually clearly established. In England, where the programme was introduced in 2012 after a severe outbreak, the frequency of illness in babies under three months fell dramatically; effectiveness against severe courses was over 90 per cent in the evaluations. Comparable figures came from the USA, Australia and Spain.

The timing: 27th to 36th week

In Austria the vaccination is recommended in every pregnancy, preferably between the 27th and 36th week. This window is not arbitrary but the result of two opposing considerations.

Not too early: the active transport of antibodies across the placenta is strongest in the final third of pregnancy. If vaccination is too early, the mother’s level has already fallen again by the time the main transport takes place.

Not too late: building up antibodies takes about two weeks. If vaccination is given in the last week, there is too little time before the birth to transfer enough.

If the vaccination is missed, it remains worthwhile all the same – up to the birth and afterwards too. After the birth it no longer protects the baby through the placenta, but it does prevent the mother herself from becoming the source of infection. In that case vaccination is given immediately in the postnatal period.

Vaccination is given again in every pregnancy, even if the last one was only a year ago. The reason is the same as above: what counts is not the mother’s protection but the level of antibodies precisely in this third trimester.

Which vaccine is used

There is no whooping cough vaccine on its own. A combination vaccine against diphtheria, tetanus and pertussis in the adult dosage is used – abbreviated dTpa, the small letters standing for the reduced antigen content. Frequently a component against polio is included as well (dTpa-IPV); that too is safe in pregnancy.

It is an inactivated vaccine. It contains no reproducing organisms but purified components, and is therefore – unlike the measles-mumps-rubella vaccine – expressly licensed and recommended in pregnancy. This distinction between inactivated and live vaccines is the single most important rule of thumb for vaccination in pregnancy.

It is well tolerated. Pain, redness and swelling at the injection site are common, occasionally tiredness or a slight fever for a day or two. In the large evaluations, in which hundreds of thousands of vaccinated pregnancies were followed up, no excess of malformations, premature births or complications was found. The worry that a short interval since a previous tetanus vaccination might do harm could not be confirmed either.

Those around the baby: the cocoon strategy

The second component is called the cocoon strategy and means: anyone who will regularly be in close contact with a newborn should be vaccinated, so that the baby does not come near the organism in the first place.

Specifically that concerns:

• the partner
• siblings – they are the commonest source of all
• grandparents who will be helping with care
• childminders, babysitters, close friends with frequent contact

For adults in Austria a dTpa booster applies every ten years, and from the age of 60 every five. Anyone around an expected baby who has not had a booster for more than five years should have one at the latest four weeks before the birth – protection is then in place when it is needed.

This recommendation is, incidentally, the only occasion in the whole of antenatal care on which the practice recommends something for people who are not its patients at all. It is made regularly nonetheless, because it works.

For completeness: the cocoon strategy alone is not enough. It has a weakness that studies made clear: it assumes that everyone who will have contact really does get vaccinated – and that is rarely achieved completely. That is why vaccinating the pregnant woman is the more reliable route: it depends on a single decision rather than five, and it works directly where the protection is needed. Vaccinating those around remains worthwhile but does not replace her own vaccination.

A practical note for families with older children: if a booster is due anyway, it is worth placing it during the pregnancy rather than afterwards. A sibling who has a booster at nursery age is thereby protected exactly during the time when there is a newborn in the house – and siblings are, as mentioned above, the commonest single source of infection.

How whooping cough runs its course

The organism is the bacterium Bordetella pertussis. It attaches to the layer of tiny hairs lining the airways and releases toxins that paralyse that layer. The cough is the consequence of the normal self-cleaning of the airways failing – and it lasts so long because regenerating that layer takes weeks.

The course divides into three parts. First one to two weeks with the picture of an ordinary cold – runny nose, slight cough, hardly any fever. It is precisely in this phase that infectiousness is highest, and precisely in this phase that nobody thinks of whooping cough. Then follow four to six weeks with the coughing fits that give it its name: staccato bursts followed by a whooping intake of breath, often with retching or vomiting at the end, and worse at night. Finally the cough fades slowly over further weeks to months – in Chinese the illness is therefore called the “hundred-day cough”.

In adults the typical picture is often missing. What remains is a dry cough that simply will not stop, that robs you of sleep and for which no reason is found. If you have been coughing for more than three weeks, have whooping cough considered – not for the sake of your own symptoms but for the people around you.

In babies the fits are frequently absent altogether. Instead pauses in breathing and poor feeding dominate. A newborn that feeds badly and turns pale or bluish needs medical assessment immediately.

Why whooping cough does not disappear

Unlike with measles or rubella, neither the illness nor the vaccination leaves lifelong protection. After an infection it lasts about ten to twenty years, after vaccination with today’s acellular vaccines less – usually four to twelve years.

Two things follow. First: adults are a large, continually renewed pool of susceptible people, and they are the reason the organism has been eradicated nowhere despite childhood vaccination programmes. Second: boosters are not a formality but necessary – with whooping cough more than with other vaccinations.

It also explains why having had the illness does not replace vaccination in pregnancy. Protection may still exist, but its antibody level is not high enough to be transferred in relevant amounts in the third trimester.

How whooping cough is diagnosed

The diagnosis is harder than you would expect, and the reason is the timing. Detecting the organism’s genetic material from a nose and throat swab by PCR is the most reliable method – but only in the first two to three weeks. After that the bacteria are often no longer detectable, while the cough is only just reaching its peak.

Later, serology helps: antibodies against pertussis toxin in the blood. It is meaningful only from about the third week of illness and is hard to interpret in the recently vaccinated, because vaccination produces the same antibodies. A single raised value therefore proves little; what matters are the level, the trend and the interval since the last vaccination.

In practice that means: anyone raising the suspicion early gets a clear answer. Anyone who waits six weeks, because the cough will stop of its own accord eventually, usually gets none. For a pregnant woman close to term and for the people around a newborn this difference is considerable – whether treatment is given and whether contacts receive preventive antibiotics depends on the diagnosis.

What else is vaccinated against in pregnancy

Whooping cough is the best known but not the only vaccination in pregnancy that is directed not at the mother but at the baby. The principle is always the same: the mother’s antibodies pass across the placenta in the final third and carry the first months of life.

Influenza. The flu vaccination is recommended in every trimester and protects twice over: pregnant women fall more severely ill than others, and babies under six months cannot yet be vaccinated themselves but become particularly ill. It is given during the flu season, irrespective of the week of pregnancy.

RSV. For a few years a vaccine against respiratory syncytial virus has been available for pregnant women, usually given between the 24th and 36th week. RSV is the commonest reason babies are admitted to hospital in their first winter. Alternatively an antibody preparation is available that is given to the baby directly. Which route applies in your case depends on your due date and on the current Austrian immunisation schedule.

COVID-19. Here too vaccination is recommended in pregnancy and transfers antibodies to the baby.

All of these are inactivated vaccines. The rule of thumb stands: inactivated vaccines are possible in pregnancy and in part expressly recommended, live vaccines such as measles-mumps-rubella and chickenpox belong before it – see rubella.

If there was contact during pregnancy

For the pregnant woman herself whooping cough is unpleasant but not dangerous for the baby: the bacterium does not cross the placenta and causes no malformations. The concern is the time after the birth.

With close contact to someone with a confirmed infection, preventive antibiotics come into question, particularly if the birth is imminent. Macrolides can be used in pregnancy; the decision depends on the timing and on how close the contact was, and belongs in a conversation rather than a reference book.

If the pregnant woman is ill herself, she is treated – again with a macrolide. Treatment shortens the cough only slightly, but ends infectiousness after a few days. Shortly before a birth, that is exactly the point.

What is provided for in Austria

The Austrian immunisation schedule provides for the dTpa vaccination in every pregnancy between the 27th and 36th week. For children their own primary immunisation begins in the third month of life as part of the six-in-one vaccine; it is included in the free childhood programme. For adults a booster is provided for every ten years, and from 60 every five.

The vaccination in pregnancy is – unlike in some neighbouring countries – not consistently free of charge in Austria; the handling differs by province and insurance fund. Ask at the practice or at the public vaccination service about the current position before letting it put you off: the cost is in the range of a few vaccine prices, while the harm prevented is not.

When the 27th week falls in your pregnancy is worked out by the due date calculator, and which examinations fall in the same window is shown by the maternity passport planner.

Where to go from here

The vaccination is discussed as part of antenatal care and can be given at the practice. Bring your vaccination card – and your partner’s, if you can find it; the commonest answer to the question about the last booster is “some time after a cut”, and that is rarely a usable basis. Make an appointment. Which vaccinations should be completed before a pregnancy is set out under rubella and in the screening planner.