What is the 100-day cough?

The nickname for whooping cough (or pertussis) says it all: Because of how long the respiratory infection can cause symptoms, whooping cough is often referred to as "the 100-day cough".

Caused by the bacterium Bordetella pertussis, whooping cough is highly contagious. It is usually spread through coughing or sneezing.

Whooping cough symptoms normally appear between a week and 10 days after being infected. They often include a runny nose and low-grade fever. The most signature symptom, however, is a coughing fit that ends with a distinctive "whooping" sound. (You can listen to what it sounds like here).

Is whooping cough dangerous?

It can be, especially in babies and young children. An unvaccinated infant who contracts whooping cough has a 1 in 20 chance of developing severe health complications that can lead to death.

Before vaccinations were widely available, whooping cough was a leading cause of death for babies and young children worldwide. About one out of every 10 children who were infected died – making pertussis more deadly than measles and polio combined.

Even today, whooping cough kills more than 150,000 children under five every year. The vast majority are unvaccinated.

One problem is that, rather than coughing, infants may stop breathing completely. This can lead to seizures and brain damage long-term.

Whooping cough outbreaks (and why we're seeing them)

Both overall rates of pertussis, and deaths caused by it, have declined globally, thanks to 75 years of effective pertussis vaccination. Today, 84 per cent of infants around the world receive all three recommended doses of the diphtheria, tetanus and pertussis (DTP) vaccine.

In some parts of the world, however, pertussis rates have risen. This includes in Western Europe, Australasia, high-income parts of the North America and southern sub-Saharan Africa.

In 2024, there have been whooping cough outbreaks and rising overall numbers in the United Kingdom, the United States and across Europe, among other countries. Some people, particularly babies, have died.

One reason for these outbreaks is the lack of full vaccination coverage across populations.

Why a whooping cough vaccine is the best protection

Once contracted, the most effective treatment for whooping cough is antibiotics, which kill the bacteria causing the infection. But antibiotics may not always relieve symptoms. People with whooping cough also can be contagious for about three weeks. This means the infection often has a lot of time and opportunity to spread to other people.

As a result, the best protection against whooping cough is vaccination. A highly effective vaccine for whooping cough was first formulated 75 years ago. In the 1940s, it was combined with inactivated bacteria that cause diphtheria and tetanus, creating the DTP vaccine.

Highly effective and safe, the DTP vaccine provides 98 per cent protection against pertussis infection. Today, the DTP vaccine is estimated to save around 13 million people per year from dying of pertussis.

Both the immediate and long-term results of the vaccines in saving children's lives have been dramatic. After the global introduction of the DTP vaccine, deaths from pertussis decreased 157-fold by 1970. In the Netherlands, for example, almost one out of every 25 deaths that occurred before the age of 20 were caused by whooping cough. After the vaccine's roll-out in 1954, that plummeted to one out of every 5,000 deaths.

Numerous large-scale studies have found no evidence that the DTP vaccine causes autism, immune system disorders or developmental issues.

Whooping cough vaccine side effects

While side effects are a risk for the DTP vaccine, as for other vaccinations and medications, they tend to be mild and temporary. They are also much more common with an older form of the vaccine, called the DTwP, than with a newer form of the vaccine, called DTaP.

The older DTwP vaccine was first formulated in the 1940s. It uses whole, inactivated pertussis bacteria. While highly effective and safe, it has a greater risk of mild, temporary side effects than newer formulations. In infants and children, the most common reactions to this older DTwP vaccine are a fever and irritability (affecting 40 to 75 per cent of children), drowsiness (affecting 33 to 62 per cent) and a temporary loss of appetite (10 to 35 per cent). Redness and swelling at the injection site are also common. More serious adverse events are extremely rare.

Despite the higher risk of temporary and mild side effects than the newer, DTaP vaccine, the DTwP vaccine also offers more protection against pertussis. It is the vaccine used most widely in low- and middle-income countries.

The newer, DTaP vaccine, created in the 1980s, is used in many uses smaller, purified fragments of inactivated pertussis bacteria. While it is also effective, the risk of side effects is lower. For this newer vaccine, the risk of fever is around 20 per cent, for example. However, temporary swelling and redness at the injection site are still common. While it is the vaccination of choice in most high-income countries, there is also some indication it might not offer as much protection as the DTwP vaccine, although it remains highly effective.

For either vaccination type, the risks of side effects must be weighed against the risks of contracting whooping cough, which can include pneumonia, brain damage and death. 

When to get a whooping cough vaccine

The World Health Organization recommends that the first dose be administered to infants at six weeks of age, the second dose at 10-14 weeks, and the third at 14-18 weeks. A fourth dose is given at 15 to 18 months of age, and a fifth dose is provided at four years old.

To protect babies who are too young to have received their jabs, pregnant women are also recommended to receive a pertussis vaccination. This is because being vaccinated in pregnancy offers 90 per cent protection to the baby between birth and being able to receive the first vaccination dose. There is no indication that receiving a DTP vaccine in pregnancy presents any risk of harm to a foetus.

Our protection from the DTP vaccine declines as we get older. That means it is also recommended that other caregivers who spend time with children, such as grandparents or other childcare providers, receive a booster.