The safety and savings depend on maintaining strong childhood vaccination rates, researchers emphasized.

“By maintaining high childhood vaccination coverage, we not only protect kids, but we may actually be able to reduce adult booster vaccinations,” said lead author Mark Slifka, Ph.D., professor of microbiology and immunology in the OHSU School of Medicine and the Oregon National Primate Research Center. “That would save $1 billion a year in the U.S. while maintaining the safety and protection of the general population.”

Slifka noted that dropping the 10-year schedule for adult boosters would more closely match guidelines recommended by the World Health Organization.

The review bolsters previous OHSU research in 2016 and in 2020 that concluded the combined vaccine produced at least 30 years of immunity, well beyond the current recommendation of every 10 years for adults from the U.S. Centers for Disease Control and Prevention. The vaccine is usually given as a combined tetanus, diphtheria and pertussis vaccine, known as DTaP.

In the U.S., childhood vaccinations are recommended six times, from infancy through age 12.

The new review suggests doing away with adult boosters altogether, as long as childhood vaccination rates remain high and the vaccine remains available on a case-by-case basis. For example, it may be necessary for someone injured in a workplace accident or car crash to receive a tetanus booster.

A natural experiment in the U.K. and France

Published recently in the journal Clinical Microbiology Reviews, the review highlights a comparison between two industrialized countries just 21 miles across the English Channel: France and the United Kingdom. Both countries have excellent childhood vaccination coverage, similar to the U.S.

“This represents sort of an experiment of nature,” Slifka said. “We have one country with over 60 million people that for decades has continued to vaccinate adults throughout their lifetime and another nearby country that also has over 60 million people, but over the past 50 years, they have never recommended adult booster vaccinations.

“The question we asked is, ‘What happens if we don’t vaccinate the adults? Are there more cases of disease or are these people protected after completing their childhood vaccination series?'”

Similar to the United States, France has a recommended booster vaccination schedule for adults. In contrast, except during pregnancy or for wound management, the United Kingdom hasn’t recommended boosters for tetanus and diphtheria beyond age 14 since the 1950s.

Yet, despite decades of adult booster vaccination, the review found that France had virtually no advantage over the U.K. in the rates of tetanus or diphtheria. In fact, the review found that the UK had a slightly lower rate overall.

In addition, “herd immunity” held strong even in 2022 when the U.K. reported an outbreak of 73 imported diphtheria cases among immigrants seeking asylum. This spike in cases was almost equal to the total number of diphtheria cases reported in the entire country over the previous 20 years combined.

“Remarkably, despite this proportionally large influx of imported diphtheria cases, there was no evidence of transmission reported among other asylum seekers who arrived by other routes or among staff or health care workers,” the authors write.

The U.K. Health Security Agency concluded that the country’s current childhood-focused vaccination program is sufficient for preventing the spread of diphtheria and that the risk to the general UK population remains low.

Strong rates of childhood vaccination are critical

The findings highlight the remarkable durability of protection following childhood vaccination against a pair of diseases that were once all but a death sentence.

In 1948, the U.S. mortality rate for tetanus was 91%. Before the introduction of antibiotics and vaccines, the mortality rate for diphtheria was roughly 50%. To this day, diphtheria kills roughly one out of 10 people who aren’t vaccinated against it.

Today, the public health threat is diminished thanks to childhood vaccinations as well as booster shots recommended in pregnancy.

“Thanks to childhood vaccinations, these diseases are incredibly rare,” Slifka said. “In fact, you’re 10 to 1,000 times more likely to be struck by lightning than to be diagnosed with tetanus and diphtheria in the United States.”

In addition to Slifka, co-authors include Archana Thomas and Lina Gao, Ph.D., of OHSU; Ian J. Amanna, Ph.D., of Najít Technologies, and Walter A. Orenstein, M.D., of the Emory Vaccine Center at Emory University.

Research reported in this publication was supported by the Office of the Director of the National Institutes of Health, award number P51OD011092. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

Now, researchers at Nagoya University in Japan and the Italian National Institute for Astrophysics (INAF) have for the first time determined how these droplets formed and accurately dated the formation of Jupiter based on their findings. Their study, published in Scientific Reports, shows how the characteristics of chondrules, particularly their sizes and the rate at which they cooled in space, are determined by the water contained in the impacting planetesimals. This explains what we observe in meteorite samples and proves that chondrule formation was a result of planet formation.

Time capsules from 4.6 billion years ago

Chondrules, small spheres approximately 0.1-2 millimeters wide, were incorporated into asteroids as the solar system formed. Billions of years later, pieces of these asteroids would break off and fall to Earth as meteorites. How chondrules came to have their round shape has puzzled scientists for decades.

“When planetesimals collided with each other, water instantly vaporized into expanding steam. This acted like tiny explosions and broke apart the molten silicate rock into the tiny droplets we see in meteorites today,” co-lead author Professor Sin-iti Sirono from Nagoya University’s Graduate School of Earth and Environmental Sciences explained.

“Previous formation theories couldn’t explain chondrule characteristics without requiring very specific conditions, while this model requires conditions that naturally occurred in the early solar system when Jupiter was born.”

The researchers developed computer simulations of Jupiter’s growth and tracked how its gravity caused high-speed collisions between rocky and water-rich planetesimals in the early solar system.

“We compared the characteristics and abundance of simulated chondrules to meteorite data and found that the model spontaneously generated realistic chondrules. The model also shows that chondrule production coincides with Jupiter’s intense accumulation of nebular gas to reach its massive size. As meteorite data tell us that peak chondrule formation took place 1.8 million years after the solar system began, this is also the time at which Jupiter was born,” Dr. Diego Turrini, co-lead author and senior researcher at the Italian National Institute for Astrophysics (INAF) said.

A new way to date when planets form

This study provides a clearer picture of how our solar system formed. However, the production of chondrules started by Jupiter’s formation is too brief to explain why we find chondrules of many different ages in meteorites. The most likely explanation is that other giant planets like Saturn also triggered chondrule formation when they were born.

By studying chondrules of different ages, scientists can trace the birth order of the planets and understand how our solar system developed over time. The research also suggests that these violent planet formation processes may occur around other stars and offers insights into how other planetary systems developed.

The study, “Chondrule formation by collisions of planetesimals containing volatiles triggered by Jupiter’s formation,” was published in the journal Scientific Reports, on August 25, 2025, at DOI: 10.1038/s41598-025-12643-x.

Funding information:

This work was supported by JSPS KAKENHI Grant Number 25K07383, by the Italian Space Agency through ASI-INAF contract 2016-23-H.0 and 2021-5-HH.0 and by the European Research Council via the Horizon 2020 Framework Programme ERC Synergy “ECOGAL” Project GA-855130.