Pertussis, also known as whooping cough, comes back unbidden. New federal data show that cases of vaccine-preventable disease this year have reached their highest level in a decade.

As of December 14, there were 32,085 cases of pertussis reported to the US Centers for Disease Control and Prevention this year. That’s a five-fold increase from the tally recorded in 2023, which saw just 6,500 cases. There are many factors to blame for the surge, experts say, including declining vaccination rates.

Pertussis because of bacteria Bordetella pertussis. The infection usually causes respiratory symptoms, especially the coughing that inspired its nickname (“whooping” refers to the noise people often make when trying to breathe after coughing). Although pertussis is usually mild in adults, the infection can be more severe in young children or other vulnerable populations, such as people with weakened immune systems.

While the first pertussis vaccine was invented more than a century agoit was not widely recommended and used until the late 1940s, when it was paired with vaccines for tetanus and diphtheria. The combination shot has been a mainstay of US immunization programs ever since, and it has helped greatly reduce the burden of pertussis. Before mass vaccination, for example, there were between 100,000 and 300,000 cases of pertussis reported annually in the US

Since 2000, the US has had tens of thousands of reported cases of pertussis. But like many infectious diseases, the covid-19 pandemic has indirectly reduced the spread of pertussis, thanks in part to people practicing social distancing. Since the world and people’s social practices have largely returned to normal, the incidence of these diseases has also increased. So at least part of the rise in cases this year may be a return to pre-pandemic trends, According to the CDC.

That said, this year’s tally is unusually high for the modern era. This is the highest number of cases seen since 2014, when there were 32,971 cases. And in some states, experts and health officials have blamed lowering the vaccination rate of residents and their children for the increase.

Another important factor has to do with the vaccine itself. In the US and many other countries, people have switched to a new, different form of the pertussis vaccine. While this the vaccine is safer than the older, whole-cell version, evidence shows that it provides less immediate and long-lasting protection from pertussis overall. As a result of this switch, experts argue that future outbreaks of pertussis are likely to be larger if they occur.

However, vaccination remains the most important tool in the prevention of pertussis, and the fewer people who are vaccinated against it, the greater the risk of persistent attacks. Worldwide—especially in countries with low vaccination coverage—pertussis CAUSE 24 million annual cases, with 161,000 deaths of children under five each year.

In the US, about 80% of children under two have it RECEIVES the recommended full series of DTaP shots, 90% of teens have received at least one shot of Tdap vaccine, and only 43% of adults over 18 have received a Tdap shot in the past ten years (recommended the boosters per decade).