Vaccines are one of medicine’s most powerful weapons against the spread of infectious diseases— but could their protection extend beyond the specific virus or bacteria they’re designed to block?
Mounting evidence suggests certain jabs given every year in the UK may also reduce the risk of seemingly unrelated illnesses, from ear infections to strokes.
Last month, scientists from Saint Louis University School of Medicine in the U.S. released a study which showed that getting the flu vaccine every winter for several consecutive years could significantly reduce the risk of dementia.
They tracked nearly 70,000 people aged over 60 and found that once people had been vaccinated for six years or more, their dementia risk dropped by an average of 14 per cent.
One theory is that repeated annual jabs gradually strengthen the ageing immune system to the point where it can prevent, or even repair, the underlying damage in the brain that causes dementia.
Vaccines are one of medicine’s most powerful weapons against the spread of infectious diseases— but could their protection extend beyond the specific virus or bacteria they’re designed to block? A woman is pictured getting her booster jab in September
This benefit probably comes from regular exposure to any type of vaccine, not just the flu one, later in life, when the risk of dementia is greatest.
Studies suggest that pneumonia jabs given to those over 65, or with chronic conditions that affect the heart, lungs, liver or kidneys, also reduce the risk of dementia by firing up the immune system enough to halt the damage to the brain.
A study by Duke University in the U.S., presented last year at the Alzheimer’s Association International Conference, showed that those aged over 65 who had the pneumonia jab were up to 30 per cent less likely to develop Alzheimer’s than those not vaccinated.
Animal research shows that vaccines increase the activity of microglia, cells in the central nervous system that remove damaged nerve cells from the brain.
One study by scientists in China, published in the Journal of Neuroinflammation in 2020, also found that injecting the flu vaccine into mice in the early stages of Alzheimer’s removed amyloid beta — the harmful deposits of protein thought to cause symptoms such as memory loss, confusion and agitation — from the brain.
Yet this phenomenon of vaccines lowering the risk of apparently unrelated illnesses is not new. For more than 40 years, the BCG vaccine once given to 14-year-olds in the UK to protect them against tuberculosis has also been used to combat bladder cancer.
It’s given to prevent tumours recurring after surgery and works in more than two-thirds of cases. Put directly into the bladder via a catheter, it ‘turns on’ local immune system cells which attack and destroy any lingering cancer cells.
Studies suggest that pneumonia jabs given to those over 65, or with chronic conditions that affect the heart, lungs, liver or kidneys, also reduce the risk of dementia by firing up the immune system enough to halt the damage to the brain
BCG is a ‘live’ vaccine, containing weakened traces of the bacterium itself, whereas the majority of UK vaccines are ‘inactivated’ — made with bacteria or viruses that have been killed.
Live vaccines, such as the measles, mumps and rubella (MMR) jab, tend to put the whole immune system on high alert rather than just the parts needed to see off a particular bug, as happens with inactivated ones. This means the immune system is more inclined to attack anything it thinks is foreign, including cancer cells.
Indeed, there are numerous other examples of jabs with broader benefits.
The shingles vaccine, offered to everyone aged 70 to 79, has been shown to reduce the risk of a stroke by up to 20 per cent, while the same pneumonia jab that appears to ward off dementia also prevents severe ear infections.
Meanwhile, a 2017 study by the University of Padova in Italy found that the yellow fever vaccine, recommended for travellers to Trinidad and parts of Africa and the Americas, reduced the risk of breast cancer by up to 54 per cent.
The researchers monitored cancer rates in more than 12,000 women given the vaccine. They said it could be suppressing inflammation that promotes tumour growth, or blocking the formation of blood vessels needed to feed a tumour.
‘Sometimes, there is a fairly straightforward explanation for why vaccines protect against other illnesses,’ says Dr Andrew Easton, a virologist at the University of Warwick.
He adds: ‘With respiratory infections such as pneumonia, there is a high risk of developing a secondary infection in the ears because bacteria there take advantage of the immune system already being under attack.’
Shingles jabs may ward off a stroke because adults infected with the varicella-zoster virus, which causes shingles and chickenpox, are up to four times more likely to experience a clot or brain bleed during the infection.
This may be due to inflammation in tiny blood vessels in the brain. ‘So if you are vaccinated against shingles later in life, you may well reduce your risk of stroke as well,’ adds Dr Easton.