A Closer Look – The Hidden Power of Vaccines
It’s well known that vaccines protect us from specific diseases. And, some vaccines can protect us not only from acute infections but also from chronic conditions. For example, the hepatitis B vaccine prevents chronic liver disease; it was also the world’s first cancer vaccine because it prevents liver cancer caused by hepatitis B infections. The human papillomavirus (HPV) vaccine prevents HPV infections, some of which become chronic and lead to the development of cervical cancer. By preventing chronic HPV infections, the vaccine also prevents a substantial number of head, neck, and anal cancers. Those long-recognized benefits aren’t hidden; they've been well-established through decades of research. But researchers are finding that certain vaccines offer benefits that go beyond their original intent.
Evidence is emerging that some vaccines may provide unexpected benefits. Two health conditions that may be positively affected by vaccination have drawn particular attention in recent years: dementia, the progressive loss of memory and reasoning caused by physical changes in the brain, and cardiovascular disease. The findings are remarkable, but the research is ongoing. Here’s what we know and what we don’t yet know.
Dementia
Dementia is a general term for symptoms affecting cognitive abilities, including memory, thinking, language and behavior. The most common type of dementia, called Alzheimer’s, is marked by progressive neuron loss and the buildup of abnormal proteins like amyloid plaques and tau tangles (neurofibrillary tangles). Beyond established risk factors, like genetics and vascular health, researchers have increasingly focused on chronic inflammation and viruses that may fuel neuroinflammation, driving cognitive decline.
A few years ago, an interesting connection between dementia and shingles vaccine emerged. Specifically, researchers took advantage of an unusual situation in Wales to study the shingles vaccine. When a live, weakened shingles vaccine (Zostavax) was introduced, eligibility was determined strictly by a person’s date of birth. People born just one day apart could end up on opposite sides of the cutoff, with only one being offered the vaccine. Those born before September 2, 1933, were ineligible for the vaccine for life, while those born after that date were eligible for vaccination. Because of the specific timing determining vaccine eligibility, researchers were able to compare the two groups. They followed the people for seven years, and they found something unexpected — those who got the vaccine were 20% less likely to develop dementia than those who did not get the vaccine.
Researchers wondered whether the finding was specific to the vaccine or if other shingles vaccines might also demonstrate this effect. The U.S. had a history with shingles vaccine use that could help answer the question. People in the U.S. had been receiving a second shingles vaccine (Shingrix), based on recombinant technology, since 2017. This vaccine is made using only a single protein from the surface of the virus. Newer adjuvants, called QS21 and monophosphoryl lipid A, caused better immune responses in older adults, so the live, weakened vaccine was replaced. To leverage this change in vaccines and learn more about the finding related to dementia, researchers conducted a large observational study of U.S. adults to compare dementia outcomes between people who received the recombinant vaccine and those who received the previous live, weakened version. Six years later, they found that recipients of the newer vaccine remained dementia free 17% longer on average than those who got the older vaccine. Interestingly, and raising more questions, women seemed to benefit more than men.
So, how might a shingles vaccine protect the brain from dementia? The evidence that is emerging suggests the shingles vaccine may reduce both the diagnosis and progression of dementia. Several mechanisms have been proposed: the vaccine may lower the risk of shingles (which itself has been linked to dementia), reduce inflammation in neurologic tissue, or counteract age-related declines in immune function. A few additional patterns stand out — the effect appears stronger in women than in men, is more pronounced with Shingrix than with Zostavax, and may reflect a delayed onset rather than outright prevention. While these results are promising, more research is needed to confirm them. For now, the clearest reason to get vaccinated remains to prevent shingles.
A few studies have also raised the possibility that other vaccines may lower the risk of dementia, including Tdap, Td and RSV vaccines.
In each of these cases, the data aren’t yet sufficient to understand exactly what the role of these vaccines may be in diminishing or delaying the onset of dementia, but the picture is likely to sharpen over time.
Cardiovascular disease
Cardiovascular disease is an umbrella term for conditions affecting the heart and blood vessels, including heart attacks, strokes and heart failure. Most cases trace back to atherosclerosis — the gradual buildup of fatty, inflammatory plaques inside artery walls — developed over a lifetime and made more likely by genetic and environmental factors, including high blood pressure, high cholesterol, smoking, diabetes and genetics. What makes these plaques dangerous isn't only their slow narrowing of the arteries, but also their tendency to suddenly rupture, triggering clots that cause heart attacks and strokes. One well-known trigger for these ruptures is certain infections.
Researchers have known for some time that influenza infections are one of these triggers, especially in adults with existing cardiovascular disease. Influenza causes a surge of systemic inflammation, raises heart rate and blood pressure, increases the body’s demand for oxygen, and destabilizes the plaques that line vulnerable arteries. In someone whose cardiovascular system is already under strain, influenza is incredibly dangerous.
If influenza can trigger heart attacks, can the influenza vaccine prevent them? A growing body of evidence suggests the vaccine can help prevent heart attacks. A systematic review and meta-analysis of patients with existing cardiovascular disease found that influenza vaccination was associated with an 18% reduction in cardiovascular death. A separate analysis of randomized trials concluded that influenza vaccination reduced major cardiovascular events by 30%, heart attacks by 26%, and cardiovascular deaths by 33%.
Some of the most remarkable findings come from patients vaccinated immediately after a heart attack. An international randomized study showed that giving an influenza vaccine within 72 hours of a heart attack was safe and significantly reduced deaths related to cardiovascular disease as well as from other causes compared with receipt of a placebo. A more recent meta-analysis incorporating these results reinforced the conclusion that vaccinating high-risk patients before they leave the hospital saves lives.
Preventing influenza infection avoids the immune reaction influenza triggers in the body, which, in the wrong patient, could lead to complications, such as rupture of an arterial plaque or fatal arrhythmia. There’s evidence that the influenza vaccine is training the immune system to guard against more than just influenza, but the most accepted theory is that the largest cardiovascular benefit comes from simply not getting sick in the first place.
The pneumococcal vaccine, recommended for older adults, has also been associated with reduced rates of stroke and other cardiovascular events in some studies. Like the influenza vaccine, this may have to do with avoiding infection in the first place. Alternatively, more like the shingles vaccine hypotheses, it may have to do with decreasing inflammatory responses. More research is needed.
What does this all mean?
Research suggests that the protection from vaccination may run deeper than we thought — that preventing certain infections might also safeguard the brain, the heart, and the body's resilience over time. None of this is settled science yet, and researchers have been careful to distinguish correlation from causation. But the direction the evidence points is encouraging, and it fits with what we already know about how chronic inflammation contributes to disease.
Even setting aside the potential additional benefits from vaccines, the diseases are themselves a compelling reason to get vaccinated. The pain from shingles can be excruciating and disabling. Influenza and pneumococcal disease send hundreds of thousands of people to the hospital and kill tens of thousands each year.
The fact that vaccines may do more than just prevent the diseases they target only strengthens the case for getting them.
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