In 2020, the rapid spread of the newly identified SARS-CoV-2 coronavirus led various global public health institutions to establish strategies to stop transmission and reduce mortality. Nonpharmacological measures – including social distancing, regular hand washing, and the use of face masks – contributed to reducing the impact of the COVID-19 pandemic on health systems in different regions of the world. However, because of the implementation of these measures, the transmission of other infectious agents also experienced a marked reduction.
Approximately 3 years after the start of the pandemic, , generating phenomena ranging from an immunity gap, which favors the increase in some diseases, to the apparent disappearance of an influenza virus lineage.
Understanding the phenomenon
In mid-2021, doctors and researchers around the world began to share their opinions about the side effect of the strict measures implemented to contain COVID-19.
In May 2021, along with some coresearchers, Emmanuel Grimprel, MD, of the Pediatric Infectious Pathology Group in Créteil, France, wrote for Infectious Disease Now, “The transmission of some pathogens is often similar to that of SARS-CoV-2, essentially large droplets, aerosols, and direct hand contact, often with lower transmissibility. The lack of immune system stimulation due to nonpharmaceutical measures induces an ‘immune debt’ that may have negative consequences when the pandemic is under control.” According to the authors, mathematical models evaluated up to that point were already suggesting that the respiratory syncytial virus (RSV) and influenza A epidemics would be more serious in subsequent years.
In July 2022, a commentary in The Lancet led by Kevin Messacar, MD, of the University of Colorado at Denver, Aurora, grew in relevance and gave prominence to the phenomenon. In the commentary, Dr. Messacar and a group of experts explained how the decrease in exposure to endemic viruses had given rise to an immunity gap.
“The immunity gap phenomenon that has been reported in articles such as The Lancet publication is mainly due to the isolation that took place to prevent SARS-CoV-2 infections. Although this distancing was a good response to combat infections, or at least delay them while coronavirus research advanced, what we are now experiencing is the increase in cases of respiratory diseases caused by other agents such as respiratory syncytial virus and influenza due to lack of exposure,” as explained to this news organization by Erandeni Martínez Jiménez, biomedicine graduate and member of the Medical Virology Laboratory of the Mexican Institute of Social Security, at the Zone No. 5 General Hospital in Metepec-Atlixco, Mexico.
“This phenomenon occurs in all age groups. However, it is more evident in children and babies, since at their age, they have been exposed to fewer pathogens and, when added to isolation, makes this immunity gap more evident. Many immunologists compare this to hygiene theory in which it is explained that a ‘sterile’ environment will cause children to avoid the everyday and common pathogens required to be able to develop an adequate immune system,” added Martínez Jimenez.
“In addition, due to the isolation, the vaccination rate in children decreased, since many parents did not risk their children going out. This causes the immunity gap to grow even further as these children are not protected against common pathogens. While a mother passes antibodies to the child through the uterus via her placenta, the mother will only pass on those antibodies to which she has been exposed and as expected due to the lockdown, exposure to other pathogens has been greatly reduced.”
On the other hand, Andreu Comas, MD, PhD, MHS, of the Center for Research in Health Sciences and Biomedicine of the Autonomous University of San Luis Potosí (Mexico), considered that there are other immunity gaps that are not limited to respiratory infections and that are related to the fall in vaccination coverage. “Children are going to experience several immunity gaps. In the middle of the previous 6-year term, we had a vaccination schedule coverage of around 70% for children. Now that vaccination coverage has fallen to 30%, today we have an immunity gap for measles, rubella, mumps, tetanus, diphtheria, whooping cough, and meningeal tuberculosis. We have a significant growth or risk for other diseases.”