Whooping cough: Why is Britain in worst outbreak in decades?

The family is not alone.

In truth, the disease has never completely vanished - although it came pretty close during the pandemic - but Scotland is currently in the grip of an outbreak that is on track to be the worst in decades.

Probably the worst since a slump in vaccine uptake during the 1970s.

Cases of whooping cough have surged in the first months of 2024, with the outbreak continuing to accelerate (Image: PHS)

Figures published on Thursday point to a rapid acceleration in the spread of the infection in recent weeks.

According to Public Health Scotland (PHS), there were 1,084 laboratory-confirmed cases of whooping cough in Scotland between January and March.

However, provisional data - which may change - previously reported that the number of confirmed cases had reached 2,232 by May 13.

On Thursday, the latest weekly update from PHS put that figure at 3,237 by June 3, suggesting that more than 1000 cases had been detected in the space of just three weeks - roughly as many as were identified in the first three months of this year.

To put that into context, the most recent major outbreak of whooping cough in Scotland - between 2012 and 2013 - notched up a total of 3,084 confirmed infections over a two-year period.

“While an increase in cases had been expected, as other respiratory infections have rebounded from the very low levels observed during the pandemic, the size of the current outbreak is alarming," said Prof Andrew Preston, an expert in microbial pathogens at the University of Bath.

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While most people will recover naturally, the disease can be dangerous - and occasionally fatal - particularly for unvaccinated infants.

In England, eight babies have died from the disease so far this year.

In Scotland, the last recorded death was in 2015, but with experts predicting that the current outbreak is likely to worsen over the coming months before peaking in autumn (based on previous seasonal trends) there is no room for complacency.

The current explosion in cases appears to be rooted in a perfect storm of falling vaccine uptake, reduced exposure during the pandemic, and the use of a vaccine where protection against infection wanes more quickly.

On the first point, Scotland appears to be faring better than other parts of the UK, but is nonetheless seeing a decline in vaccine coverage.

Childhood vaccine uptake has been falling (dark blue = 6-in-1 vaccine, including pertussis) (Image: PHS)

Babies get their primary immunisation against whooping cough from three doses of the "six-in-one" vaccine at eight, 12, and 16 weeks of age (in addition to pertussis, it protects against polio, diphtheria, tetanus, Hib B, and Hepatitis B).

This is topped up by a booster jag aged three.

Between 2015 and the end of 2023, the percentage of one-year-olds in Scotland covered by the primary course dwindled steadily from 97.3% to just under 94.8%.

The percentage of five-year-olds who had received their booster by the time they started school had also eroded from around 94% to 90%.

These are small changes, but that can be enough to make a difference when a disease is as highly contagious as pertussis.

To look at the figures another way, it means that there are roughly twice as many unvaccinated infants now as there were ten years ago.

There is also regional variation: in Highland, which has come under fire for problems in its vaccination service since switching from GP to health board delivery in March last year, just 88.9% of babies who turned one by the end of 2023 had been inoculated against whooping cough, the lowest rates anywhere in Scotland (as recently as December 2021, it was over 95%).

Pregnant women can be vaccinated against pertussis to protect their newborn baby (Image: Getty)

The picture for maternal vaccination is also patchy.

Pregnant women are encouraged to get vaccinated so that they can pass the antibodies onto their unborn babies in the womb, giving them protection against a range of infectious diseases - including whooping cough - during the first weeks of life.

According to data recently obtained by the Herald, uptake varies from 73% in Tayside and Grampian to more than 95% in Orkney, although a number of health boards - including Highland, Dumfries and Galloway, and Shetland - did not provide figures.

Nonetheless, this appears notably higher than the average of around 60% in England, including lows of 37% in London.

The pandemic also played a role, however.

During 2021 and 2022, there were just seven confirmed cases of whooping cough in Scotland; in a normal year there would typically be 500-800.

Social distancing was designed to curb the transmission of Covid, but it stopped most other respiratory bugs from circulating too.

Just as we saw a massive rebound in influenza at the end of 2022, we are now seeing a resurgence of pertussis in a population with reduced immunity from a lack of recent exposure.

Finally, there is the vaccine.

Before the pertussis was added the routine schedule of childhood vaccinations in the 1950s, there were around 150,000 known whooping cough cases every year in Britain and more than 300 deaths.

Initially, the NHS deployed a "whole cell" vaccine formulated using an inactivated form of the pertussis bacteria.

This provided very long-lasting protection against infection as well as serious illness, but uptake collapsed in the 1970s following claims of rare complications resulting in brain damage.

Vaccine coverage fell in the late 1970s and 1980s, resulting in previous substantial outbreaks of whooping cough (Image: ILELTS)

Significant outbreaks of pertussis occurred as a result in the late 1970s and 1980s.

Although uptake recovered, the UK eventually switched to an acellular form of the vaccine in 2004 which contains protein fragments from the dead bacteria instead.

It is associated with fewer side effects, but has also been blamed for the pattern of cyclical whooping cough outbreaks over the past 20 years because - while protection against serious illness and death remains robust - immunity against infection wanes much more rapidly, generally fading within seven to 10 years.

This has led to some debate about whether the switch between vaccine types has done more harm than good, a controversy which this current outbreak - affecting not just the UK, but Europe - is reigniting.