The U.S. Vaccine Risk Factor: Trends and Disparities

Vaccines are a key preventive medical tool that keep millions of adults and children safe from potentially debilitating or even fatal diseases and afflictions. But some vaccines can cause serious adverse effects.

With 10 children reportedly dying following vaccination against COVID-19, vaccine safety, continuous safety monitoring, further investigation of side effects, and transparent communication are all paramount issues.

In this study, we’ll consider the link between some vaccines and severe side effects, and who is most at risk; we’ll also look at public confidence in vaccines, and who is rejecting them (and where); and we’ll examine the connection between vaccine skepticism and a spike in cases of some dangerous diseases.

Let’s first consider the links between COVID-19 vaccines and serious illness (and fatalities).

The COVID-19 Vaccine and Links to Myocarditis

U.S. Centers for Disease Control and Prevention (CDC) data confirms that, since the onset of COVID-19, the virus has claimed the lives of over 2,000 children and teenagers, 700 of whom were just one year old or younger.

Additionally, a member of the U.S. Food and Drug Administration (FDA) has linked COVID-19 vaccines to the deaths of 10 children.

In doing so, Dr. Vinay Prasad referenced myocarditis (a rare heart inflammation linked to mRNA COVID-19 vaccines) as the key factor. Dr. Prasad also disputed the widely accepted notion that the overall benefits of vaccination are greater than the potential risk of side effects.

Studies have revealed that young males (in particular, those between the ages of 12 and 30) have a disproportionate chance of developing myocarditis after receiving the vaccine. Data also confirms that 81% of the people who experienced myocarditis completely recovered within around 3 months.

That said, one study found that people who suffer from COVID‑19 are over seven times more likely to subsequently develop myocarditis than people who get the vaccine. Additional key study assertions included the following.

• About 61% of all myocarditis cases occurred in men, with younger people also disproportionately likely to be affected.
• Myocarditis cases after vaccination were extremely rare and usually mild: only 1.07% of cases required a hospital stay, and just 0.015% resulted in death.
• Among the vaccines studied, Moderna’s showed the highest myocarditis rates, though still far below levels due to COVID‑19 infection.
• Studies from the U.S. and Mexico reported nearly three times higher myocarditis rates than studies from Europe and other parts of the world.

Following such reports of some severe vaccine side effects (even when reports are offset by studies that play down such effects), it’s unsurprising to discover diminished confidence in vaccines.

Levels of Vaccine Confidence

According to a KFF poll, most U.S. adults suggest they’re at least ‘somewhat confident’ in the safety of most vaccines, including those used to combat measles (83%), pneumonia (82%), shingles, and the flu (74%).

Yet this public confidence does not extend to the COVID-19 vaccine, with contrasting expert opinion adding to the equivocation, and worries around vaccines prompting a surge in public health complaints.  

Just over half (56%) of canvassed adults say they’re at least ‘somewhat confident’ about the safety of COVID-19 vaccines. In terms of a political spread of that 56%, nearly nine in ten Democrats (87%), just over half of independents (55%), and only three in ten Republicans expressed confidence.

This national ambivalence has already begun to influence vaccine take-up.

Vaccine Exemptions

Study data show that an increasing number of kindergarten children are getting nonmedical vaccine exemptions. For the 2024-25 school year, 3.6% of kindergarteners were exempted from vaccination, up from 2.2% in 2014-15.

Medical exemption rates for all reporting states for the 2024-25 school year were below 1%, reflecting the fact that nonmedical exemption rates are rising due to parental personal choice. 

Nonmedical exemption rates remained at around 2% between 2014 and 2020, before slowly rising thereafter in each successive year.

To pinpoint the areas featuring the most nonmedical vaccine exemptions, here are the percentages of vaccine exemptions for the top ten states, with Idaho ranking first by a significant margin.

ABC News suggests that a combination of rural states lacking enough medical providers and hesitancy over COVID-19 ‘inadvertently spilling into concerns about other vaccines’ are at the root of high exemption rates.

Top Ten States Featuring the Most Nonmedical Vaccine Exemptions (2024-2025 School Year)

In the U.S., vaccine exemptions fall into two categories: medical and nonmedical. States set their own exemption laws, with medical exemptions usually granted if a child has a health condition that makes vaccination unsafe, like a severe allergy to a vaccine ingredient or a weakened immune system from cancer treatment. 

When it comes to nonmedical exemptions, they’re often due to a family’s beliefs and might be religious (when vaccination conflicts with a family’s faith) or philosophical (when parents object for personal or moral reasons).

All states now allow medical exemptions, whereas rules for nonmedical exemptions vary. Most states permit religious exemptions, fewer allow philosophical exemptions, while some states allow both.

Whatever the motivations behind the rise in vaccination exemptions, there’s a clear link between the declining number of vaccinated children and another rise: national cases of measles.

A Rise In Measles Cases

During the 2024-2025 school year, vaccination coverage among U.S. kindergartners decreased (for all reported vaccines) compared to the 2023-2024 school year.

Levels of coverage ranged between 92.1% for diphtheria, tetanus, and acellular pertussis vaccine (DTaP) to 92.5% for the measles, mumps, and rubella (MMR) and polio vaccines.

Other key data points include:

• The number of kindergartners who attended school without documentation confirming the completion of the MMR vaccine series rose to about 286,000 during the 2024-2025 school year
• Vaccine exemptions increased in 36 states and in the District of Columbia, while 17 states reported exemption rates that exceeded 5%
• 138,000 kindergartners were exempt from one or more vaccines during the 2024-2025 school year.

As of December 16, 2025, a total of 1,958 confirmed measles cases were reported in the United States (1,934 across 44 jurisdictions; 24 by international visitors to the country). The age breakdown of the 1,958 people who contracted the disease is as follows.

• Under 5 years-old: 512 (26%)
• 5-19 years-old: 808 (41%)
• Over 20 years-old: 625 (32%)
• Unknown: 13 (1%)

And the vaccination status of those who contracted the disease was as follows.

• Unvaccinated or Unknown: 93%
• One MMR dose: 3%
• Two MMR doses: 4%

In 11% of cases, those suffering from measles were hospitalized (222 of the 1,958), and three people died. The age proportion of those with measles who were hospitalized was:

• Under 5 years-old: 20% (103 of 512)
• 5-19 years-old: 6% (48 of 808)
• Over 20 years-old: 11% (71 of 625)
• Unknown: 0% (0 of 13).

As a comparison that highlights the rise in cases, the number of measles cases reported in the United States during recent years was:

• 285 in 2024
• 59 in 2023
• 121 in 2022
• 49 in 2021.

Additionally, 49 outbreaks were reported in 2025, with 88% of confirmed cases (1,713 of 1,958) being outbreak-associated. 

For comparison, 16 outbreaks were reported during 2024, and 69% of cases (198 of 285) were outbreak-associated.

A measles outbreak is defined as three or more related measles cases that lead to a rapid expansion of case numbers. Most outbreaks start as small clusters of affected people, usually residing in the same household.

When this cluster then mixes with their local community (especially one featuring a low vaccination rate), the disease can spread quickly. 

This was exemplified by what happened in Ohio in 2022, when 85 locally acquired cases were confirmed over a 42-day period. During the previous year (2021-2022), kindergarten-entry 2-dose MMR vaccination coverage in Ohio (88.3%) was around 5% lower than the national average (93%).

But what does an up-to-date national measles picture look like? Here are the U.S. states that featured the highest number of measles cases in 2025.

States With The Highest Number Of Measles Cases (2025)

The Texan measles outbreak (the largest measles outbreak in the U.S. for several years, and which has extended into 2026) began in a close-knit Mennonite community in West Texas, before subsequently spreading to other under-vaccinated areas. It offers the perfect example of how quickly an outbreak can occur in low-vaccination areas. 

At the other end of the scale, some states (eight) reported no cases of measles. Here are those states, plus two states that recorded a single case of measles apiece.

States With The Lowest Number Of Measles Cases (2025)

Delaware, the District of Columbia, Maine, Massachusetts, Mississippi, New Hampshire, North Carolina, and West Virginia are all effectively tied in first place with no cases of measles. Alabama and Connecticut, with one measles case apiece, were also virtually measles-free.

Regarding comparative susceptibility and immunity, one study found a direct correlation between state political inclination and the reporting of Adverse Events (AE) pertaining to the COVID-19 vaccine. The study suggests that Republican states disproportionately feature vaccine recipients and clinicians much more likely to report AEs

The cross-sectional study of 620,456 AE reports found that a 10% increase in state Republican voting was associated with a 5% increase in the likelihood that a COVID-19 vaccine AE would be reported, and a 25% increase for severe AEs reported. In terms of state political affiliations, the number of unvaccinated and measles-affected people augments this correlation.

When we look at a breakdown of gender differentials regarding adverse effects to vaccines, we can see a clear disparity.

Gender Side-Effect Disparities

A quick look at the figures for a female/male share of adverse side effects reported after one dose of a vaccine (that resulted in recovery) of 45,843 recorded adverse cases:

• 31,018 were female
• 14,688 were male
• 137 were unconfirmed or unaccounted for.

35,368 of the total side effects were due to the COVID-19 vaccination, with 684 due to the measles vaccination.

There were 7,259 fatal one-dose cases recorded between 2020 and 2025, with 4,348 males dying. The five main states for male deaths were as follows.

Of the 2,847 females who died following one vaccination dose, the main states involved were as follows.

Kentucky is a major outlier with 757 total deaths from the first COVID-19 dose, numbers three times higher than projected, based on the state’s population.

Overall, while more men died following a single vaccine dose, women suffer far more adverse events following vaccination. And, if we focus on post-vaccination fatalities among the 3-17 age group, of 34 recorded fatalities, 23 were female, 11 male.

And such data varies across different vaccination producers/suppliers. Here’s a rundown of vaccine brands and their associated fatality numbers.

And here are the ten states that featured the highest number of deaths following a single dose of vaccination between 2020 and 2025.

Conversely, here are the states with the least number of vaccination deaths.

Beyond fatalities, here are the states that reported the highest number of side effects from the first COVID-19 dose, with California far ahead in first place, and other large metro areas also highly placed.

And here’s the flipside list of states subject to the lowest number of adverse dose effects.

 

Vaccines and Side Effects in the U.S.

So, there’s a clear correlation between vaccination levels, confidence in or adherence to the use of vaccines, and outbreaks of diseases such as measles.

Additionally, a state’s political affiliation will in some way determine the likelihood that its residents will both use and report adverse effects regarding vaccines.

And although more men than women suffer fatalities after taking a vaccine, some studies suggest that more female children suffer from fatalities than male children, and that more women suffer from adverse responses to vaccines.

Whatever the motivations behind the rise in vaccination exemptions, there’s a clear link between the declining number of vaccinated children and another rise: national cases of measles

Ultimately, it’s a situation wrought with complexity. Depending on someone’s state of residence and belief system, their fear around vaccines may be amplified, which may subsequently influence their trust in the kind of medical protections that can make all the difference between serious illness (or even death) and good health. One result is a still ongoing measles outbreak in Texas, the biggest the U.S. has seen in many years.

And yet, despite this, there’s also compelling data to suggest that vaccines can cause multiple serious issues, such as myocarditis (offset by contrary data suggesting the affliction the vaccination is meant to repel is far more dangerous).

Overall, until vaccine trust is universal across the United States, such problems may well persist. Since vaccines have historically featured a built-in risk element, this seems unlikely, and with a rising number of children exempt from vaccination, the potential for further outbreaks is a significant worry.