Males and females often respond differently to vaccines, but the benefits seem to be equal until age 65. When females reach that age, some vaccines may be even more beneficial for them than they are for males.
In fact, a new study found that a new shingles vaccine, known as Shingrix, provided protection not just against shingles but also against dementia, particularly among women.
“This latest research underscores how we are discovering new ways that vaccines can benefit not just children but older Americans, too,” says Gabriela M. Andujar Vazquez, MD, an infectious disease doctor and epidemiologist at Dartmouth Health’s Dartmouth Hitchcock Medical Center (DHMC).
Here’s more about what we know about vaccines, their effectiveness, and what scientists are learning about the benefits they bring.
Who benefits
Vaccines have long been considered a simple, safe, and effective way of protecting people against harmful diseases.
The World Health Organization (WHO) reports immunizations from vaccines prevent 3.5 million to 5 million deaths every year from diseases like diphtheria, tetanus, pertussis (whooping cough), influenza (flu), and measles.
And while most vaccinations are given to children from birth up to age six, with follow-up booster doses in their preteen and adult years, some vaccines are given to prevent diseases in adults.
These include vaccines for COVID-19, flu (influenza), RSV (respiratory syncytial virus), pneumonia (pneumococcal virus), shingles, and diseases protected under Tdap, such as whooping cough and diphtheria.
As a guideline, the U.S. Centers for Disease Control and Prevention (CDC) provides a list of vaccines for children and adults by age.
In its list, the American College of Obstetricians and Gynecologists (ACOG) includes vaccines for women during pregnancy.
“Vaccines in pregnancy not only protect the pregnant patient but also their babies after birth by the transport of antibodies across the placenta. For this reason, we strongly recommend vaccinations in each pregnancy to whooping cough, which can be dangerous to babies, along with influenza and RSV vaccines during their active seasons,” says Ella A. Damiano, MD, Obstetrics & Gynecology, DHMC.
How vaccines work
According to the CDC, vaccines work by getting the body to defend itself against a disease without the dangers of a full-blown infection.
The active ingredient in all vaccines is an antigen, a substance that triggers the immune system to produce antibodies that fight disease. Depending on the vaccine, the CDC says an antigen might be:
- Weakened or killed bacteria or viruses
- Bits of the virus or bacteria's exterior surface or genetic material
- Bacterial toxin that is treated to make it non-toxic
“Because vaccines contain only killed or weakened forms of germs like viruses or bacteria, they do not cause the disease or put you at risk of its complications,” explains the WHO.
What do vaccine efficacy and herd immunity mean
A vaccine’s efficacy tells you how much the vaccine lowers risk, says the WHO.
If, for example, a vaccine has 80% efficacy, it means that 80% fewer people will contract the disease when they come into contact with the virus.
“The high rates of efficacy show just how important these vaccines are in stopping the spread of disease,” says Andujar Vazquez, who was recently appointed to the Healthcare Infection Prevention Advisory Group (HIPAG), a joint initiative of the Society for Healthcare Epidemiology of America (SHEA) and the Association for Professionals in Infection Control and Epidemiology (APIC).
For highly contagious viruses like measles, at least 95% of a population must be vaccinated to maintain what is known as herd immunity.
Herd immunity occurs when a significant portion of a population becomes immune to an infectious disease, limiting further disease spread.
“A vaccine’s effectiveness is about more than just preventing illness in the person who receives it. When vaccines reduce the chance of infection after exposure, they also reduce the opportunities for a virus to spread from person to person. This is why vaccines are such an important tool for protecting both individuals and communities,” says Andujar Vazquez.
This recently released review shows how important that protection can be, reporting that the 2025-2026 COVID-19 vaccine reduced emergency department and urgent care visits by 50% and hospitalizations by 55%.
“Even when infections occur, vaccinated individuals are often less likely to develop severe disease, be hospitalized, or experience complications,” Andujar Vazquez explains.
Vaccines and older adults
Vaccines are especially important for older adults because this age group faces increased risk from vaccine-preventable diseases, including flu, RSV, and pneumonia.
That’s in part because of changes in the immune system that make older people more vulnerable to a variety of infections.
According to the National Foundation for Infectious Diseases, respiratory infections such as flu, RSV, and pneumonia cause more hospitalizations and deaths in people over 65 than in younger people.
“Vaccines for these respiratory illnesses help reduce severe disease, prevent hospital stays, and help maintain your independence,” the foundation states.
And while the CDC found that fewer adults aged 65 and older reported getting vaccinated against flu or pneumonia in 2024 compared with 2019, recent studies like this one show that vaccines can not only prevent high-risk infections but also better balance the immune system and reduce inflammation.
“It is essential that older people get their vaccines,” says Andujar Vazquez.
Gender differences in side effects
All that said, vaccines can have side effects.
While age may reduce the strength of your immune response, females across all age groups tend to produce greater vaccine-induced immune responses and side effects than males.
Depending on the vaccine and other factors, side effects can include fever, aches and pains, fatigue, or injection-site swelling.
But doctors stress that side effects are usually not a bad thing, because they show that the vaccine is successfully getting your body to protect itself against future infection. Once more, most side effects are mild and last one to three days.
Women report higher rates of side effects from vaccines to diseases that include:
- Influenza (Flu)
- Yellow Fever
- Human Papillomavirus (HPV)
- Measles, Mumps, and Rubella (MMR)
- Hepatitis A & B
- COVID-19
- Shingles
“People just do sometimes react differently,” says Andujar Vazquez.
At the start of the COVID-19 epidemic, for example, women reported more side effects from these vaccines than men.
But a later study found no significant gender differences in the efficacy of COVID-19 vaccines, despite a greater antibody response, especially in younger populations.
Why some women have a stronger response to vaccines
Some attribute the stronger antibody response in women as being tied to an evolutionary need: providing protection to the developing embryo.
Evolutionary explanations aside, the hormone estrogen likely plays a role.
Estrogen, primarily considered a female sex hormone, is thought to make immune cells work harder, enhancing immunity.
In contrast, the presence of the hormone testosterone, which is more prevalent in males, is thought to suppress that cellular behavior.
Genetics could be a factor
Studies suggest that the X chromosome may influence immunity, playing a key role in determining how well an organism’s immune system functions.
Females have more of the X chromosome, as the XX chromosome pattern is the biological blueprint that typically directs the development of female physical traits and reproductive organs.
XY typically directs the development of male traits.
The reason we don’t know more about how women specifically respond could be attributed to a number of factors, including:
- Women of childbearing age being excluded from early-stage clinical vaccine trials
- Male-dominated animal studies with vaccines
- Clinical trials historically using a single universal dose that masks sex-specific differences in efficacy and side effects
- A lack of data separated by biological sex
Why older women might benefit from vaccines more than older men
More gender-based research is needed.
But studies like this one suggest that vaccines protect women aged 65 and older more against influenza, tetanus, pertussis, shingles, and pneumococcal infections than men at that age, and that the difference might be explained by women’s antibodies declining more slowly with age.
Experts have also noted that taking a closer look at sex-based immune differences could prove critical to developing targeted interventions for age-related disease.
The recent study of the effects of the recombinant shingles vaccine Shingrix, conducted by researchers at Oxford University, is encouraging.
It reported a 17% reduction in dementia diagnoses six years after the vaccination. That reduction, the study said, equated to 164 or more days without dementia.
What was particularly interesting to Karen E. Blackmon, PhD, a neuropsychologist at DHMC and co-director for the Brain Health Navigator program, was that the protective benefit was stronger in women than men; 22% of women versus 13% of men had more time lived diagnosis-free.
“Women are already at higher risk for both shingles and Alzheimer’s disease, and they tend to mount stronger immune responses to vaccines,” she says, pointing to the fact that after menopause, the loss of estrogen’s protective effects on the brain may make women more vulnerable to the kind of viral-driven inflammation that shingles vaccination could prevent.
“More work is needed to confirm the dementia prevention benefits through clinical trials, but the vaccine’s proven benefits against shingles, combined with its favorable safety profile, make a compelling case for broader uptake among older adults,” Blackmon concludes.
