April 3 — Since the beginning of this year, the number of pertussis cases in China has risen significantly, and "pertussis resurgence" once trended on social media. According to national notifiable infectious disease surveillance data released by the National Disease Control and Prevention Administration, in the first two months of this year, the number of pertussis cases was 32,380, nearly 23 times the number in the same period last year.

This phenomenon has also drawn the attention of disease control authorities. "At present, pertussis prevention and control in China requires great attention." Shen Hongbing, deputy director of the National Disease Control and Prevention Administration and director of the Chinese Center for Disease Control and Prevention, said this at the "2024 Vaccine and Immunology Conference" held on March 16.

Pertussis, this "ancient" disease, seems to have made a comeback.

The population is generally susceptible

Pertussis is an acute respiratory infectious disease caused by Bordetella pertussis and is a Class B notifiable infectious disease in China. The course of the disease is relatively long, and typical cases may present with a cough lasting 2-3 months, hence the name "pertussis" (whooping cough).

Hu Yang, deputy director of the Department of Respiratory and Critical Care Medicine at Shanghai Pulmonary Hospital, told China News Health that the early stage of pertussis infection may present with symptoms of upper respiratory tract infection such as fever, sneezing, and cough, similar to the common cold, which makes pertussis relatively easy to be missed in diagnosis. "If the cough persists, especially if the cough symptoms become increasingly severe, be sure to seek medical attention promptly," he warned.

According to the "Pertussis Diagnosis and Treatment Protocol (2023 Edition)" (hereinafter referred to as the "Protocol") issued by the National Health Commission, the incubation period of pertussis is generally 7-14 days, and patients are infectious from the start of the incubation period until 6 weeks after onset, with the highest infectivity from the end of the incubation period to 2-3 weeks after symptoms appear, and the population is generally susceptible.

Hu Yang said that among pertussis cases, children are more commonly seen and adults relatively fewer, with newborns and infants under 3 months of age being a high-risk group. "Their airways are relatively narrow to begin with, and when spasmodic coughing and the whooping inspiratory sound appear, if treatment is not timely enough, it may lead to suffocation and even death."

Why has the incidence risen significantly?

In fact, not only in China but in many regions around the world, the incidence of pertussis has shown an upward trend. The Protocol points out that due to the waning of immunity after vaccination and mutations in Bordetella pertussis, many countries with high vaccine coverage have seen "pertussis resurgence," with the peak age of onset shifting from infants and young children to adolescents and adults, and adolescents and adults becoming the main source of infection for pertussis in infants.

Experts interviewed by China News Health analyzed that the upward trend in pertussis incidence may be affected by multiple factors, including improved detection technology and the relatively short duration of protection after vaccination.

Zhao Wei, director of the Biosafety Research Center at the School of Public Health of Southern Medical University, said that pertussis epidemics occur about every 2-5 years, and its transmission had long been severely underestimated globally. The current epidemic is related both to pertussis entering an epidemic period and possibly to a marked increase in reported pertussis incidence under active surveillance. But regardless of the cause, relevant departments need to pay attention.

In Hu Yang's view, the cause of this situation is not yet clear; generally speaking, it may be related to strain mutation or a decline in host immunity against Bordetella pertussis.

Regarding the reasons for the increased incidence of pertussis among adolescents and adults, Zhao Wei analyzed that in the past, healthy adults had strong immunity, and even if infected with Bordetella pertussis, they often showed asymptomatic infection or mild symptoms, serving as an important source of hidden household transmission. "During the COVID-19 pandemic, because the public consciously took strict respiratory protection, opportunities for respiratory infectious disease infection decreased, which objectively also led to a decline in specific immunity against Bordetella pertussis. Under active surveillance, the post-pandemic period will show an expansion of the population range of pertussis infection."

"Considering adjusting immunization program strategies"

Vaccination with pertussis-containing vaccines remains an effective means of preventing pertussis. According to the national immunization program schedule, children should receive one dose of pertussis-containing vaccine at 3, 4, and 5 months of age and one dose at 18 months of age.

"Neither vaccination nor natural infection can produce lifelong immunity, but vaccination can reduce the risk of severe illness and death," Shen Hongbing said at the "2024 Vaccine and Immunology Conference."

He pointed out that since 2014, the incidence of pertussis in China has shown an upward trend. "Pertussis prevention and control requires attention. The National Disease Control and Prevention Administration needs to hold a special meeting to study whether our immunization program policies need adjustment and what changes are needed for vaccines; these are worth considering."

Zhao Wei agreed with this. He believes that China needs to further strengthen active surveillance of pertussis-like symptoms and promptly identify potential sources of infection among adolescents and adults in order to effectively interrupt the chain of transmission. Considering that the outbreak may be related to a decline in population-specific immunity, if the epidemic further expands, booster vaccination can be carried out for preschool children at high risk of pertussis infection.

Regarding personal protection, Hu Yang said that vaccines work most of the time, but that does not mean they can completely prevent infection. In addition to vaccination, staying away from infected persons, wearing masks as much as possible, washing hands frequently, and maintaining a reasonable daily routine and physical exercise are also effective means of avoiding infection.