Over the last two decades, there has been a resurgence of pertussis though primary immunization with pertussis vaccination is widely practiced. As vaccine immunity wanes within 4–12 y of vaccination, it may not be effective in preventing outbreak cycles of pertussis which occur every 3 to 5 y [1] adversely affecting the unimmunized or incompletely immunized infants <6 mo of age, the population most vulnerable to pertussis [2]. Infant pertussis is also known to be associated with greater morbidity in view of longer hospital stay, need for ICU care and greater mortality [3].

Even though pertussis is a notifiable disease in India, there is limited data on disease burden due to the deficiency of a robust national disease surveillance system, lack of awareness among medical professionals and non-availability of diagnostic facilities. This leads to gross under-reporting and a poor estimate of its true burden and its consequences especially among infants [4]. The study by Singh et al. in this issue of the journal seeks to estimate the burden of pertussis in <6 mo old infants in multiple sites across India [5].

The study uses the revised CDC 2020 case definition for the diagnosis of pertussis, with laboratory confirmation using RT-PCR for Bordatella pertussis and also other potential viral and bacterial pathogens. The study reports 8.5% laboratory-confirmed pertussis (LCP) and 11.5% probable pertussis (PP) among the 400 infants in the study that fit the CDC clinical case definition. Among those with LCP, 19/34 (55.88%) had received at least one dose of pertussis vaccine raising concerns about primary vaccination efficacy and seroconversion, ‘interference’ or ‘blunting’ of the infant’s immune system due to maternal pertussis vaccination and differences in seroconversion with the usage of acellular pertussis vs. whole cell pertussis vaccines. On evaluation of the symptoms of those with LCP, only 9% had a cough duration of >2 wk, 15% had inspiratory whoop, 23.5% had post-tussive vomiting and 23.5% had apnea (with/without cyanosis). Over reliance on these criteria in the clinical case definition of pertussis would lead to under-diagnosis of pertussis, especially in young infants. It also emphasizes the need for molecular testing to diagnose pertussis in this vulnerable population. Another interesting finding was that only 58% these young infants had received their age appropriate vaccines and over 70% of those infected <3 mo of age were in those that did not receive age appropriate vaccination. The effect of the COVID-19 pandemic on routine childhood vaccination may have played a role in the low coverage of age appropriate vaccines. Ensuring age appropriate vaccination is as important as the availability of effective vaccines.

After decades of use of pertussis containing vaccines, this study highlights the continued burden of disease in young infants who are the most vulnerable. Maternal Tdap vaccination is the solution to curb infant pertussis and the Global Pertussis Initiative has endorsed the effectiveness of Tdap vaccination in the third trimester of pregnancy in preventing pertussis in young infants and its safety in pregnancy [6]. Further research is required to study whether immunization during pregnancy causes ‘blunting’ of the infant antibody responses for the same or related antigens after primary vaccination.