Chickenpox. Whooping cough. Measles. You may have heard about outbreaks of these illnesses and thought, Didnt we end those with vaccinations?

But the only communicable disease that we have eradicated using vaccines is smallpox, which explains why you likely never received a shot for it if you were born in the U.S. after 1972.

Measles , which infected almost half a million people annually before the vaccination was licensed in 1963, was declared eliminated from the U.S. in 2000, a historic public health achievement. This means that outbreaks happen only when someone brings the virus into the U.S. from another country, which, given the high rate of international travel, does occur.

In 2019, there was a sharp uptick in the number of cases of measles reported in the U.S. 1,274 that calendar year. This was the highest number of cases reported in one year since 1992, and the majority of these were among unvaccinated individuals.

So far in 2024, there have been 269 reported cases of measles, including 14 outbreaks (consisting of three or more related cases). Again, the majority of people who got sick (88%) were unvaccinated or their vaccination status was unknown. Forty-one percent were under 5 years old. It makes sense that young children would be most affected, since most babies do not receive their first dose of the MMR (measles mumps rubella) vaccine until they are 12 months old.

This year, whooping cough (pertussis) has been in the news. The number of cases has risen to five times that of 2023 rates. However, it should be noted that this increase marks a return to pre-pandemic numbers. Cases of whooping cough dropped dramatically during the pandemic when social-distancing measures were in place. Unlike measles, whooping cough is considered endemic, or common, in the U.S. Though vaccines against whooping cough (DTaP and Tdap) work well, their effectiveness wanes over time, meaning that older children may be able to spread the disease again if they do not receive booster shots. (Note that it is recommended that pregnant people receive a vaccine in order to provide their infant with short-term protection from the illness.)

Vaccines are an essential tool when it comes to preventing outbreaks of disease, yet vaccination rates have been going down. From the 2019-2020 to the 2022-2023 school years, the number of kindergarteners who had received all of their recommended vaccines dropped from 95% to less than 93%. The number of students who received exemptions from vaccine requirements also rose from 3% in 2022-2023 to 3.3% in 2023-2024. This is the fourth year in a row that rates have missed the Department of Health and Human Services Healthy People 2030 goal of 95% of kindergarteners having received the MMR vaccine. For measles, experts say that 95% is the rate of vaccination necessary to achieve herd immunity, meaning that enough people in the community are vaccinated to protect the minority (such as babies) who are not. (The rate needed to achieve herd immunity is different for other diseases.)

With declines in routine childhood vaccination, more communities across the U.S. may be at risk for experiencing outbreaks of vaccine-preventable diseases, Jasmine Reed, a spokesperson for the Centers for Disease Control and Prevention, told HuffPost.

Vaccination is the best way to prevent these outbreaks and their devastating impact on children, Reed said.