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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, it is evident that SARS-COV-2 has also impacted the dynamic of other infectious agents, 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 co-researchers, 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 Boulder School of Medicine in Denver, grew in relevance and gave prominence to the phenomenon. In the commentary, 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 Medscape Spanish Edition by Erandeni Martínez Jiménez, biomedicine graduate and member of the Medical Virology Laboratory of the Mexican Institute of Social Security (IMSS), at the Zone No. 5 General Hospital (HGZ/MF), 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, MHS, PhD, of the Center for Research in Health Sciences and Biomedicine (CICSaB) of the Autonomous University of San Luis Potosí (UASLP) School of Medicine in 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.”
Lineage Extinction
Three types of influenza viruses — A, B, and C — cause infections in humans. Although influenza A virus is the main type associated with infections during seasonal periods, as of 2020, influenza B virus was considered the causative agent of about a quarter of annual influenza cases.
During the onset of the COVID-19 pandemic, cocirculation of the two distinct lineages of influenza B viruses, B/Victoria/2/1987 (B/Victoria) and B/Yamagata/16/1988 (B/Yamagata), decreased significantly. According to data from the FluNet tool, which is coordinated by the World Health Organization, since March 2020 the isolation or sequencing of viruses belonging to the Yamagata lineage was not conclusively carried out.
Specialists like John Paget, PhD, from the Netherlands Institute for Health Services Research (Nivel) in Utrecht, have indicated that determining the extinction of the B/Yamagata lineage is critical. There is the possibility of a reintroduction of the lineage, as has occurred in the past with the reemergence of influenza A (H1N1) in 1997, which could represent a risk in subsequent years.
“In the next few years, research related to viruses such as influenza B and the impact on population immunity will be important. Let’s remember that influenza changes every year due to its characteristics, so a lack of exposure will also have an impact on the development of the disease,” said Martínez Jiménez.
Vaccination Is Essential
According to Comas, the only way to overcome the immunity gap phenomenon is through vaccination campaigns. “There is no other way to overcome the phenomenon, and how fast it is done will depend on the effort,” he said.
“In the case of COVID-19, it is not planned to vaccinate children under 5 years of age, and if we do not vaccinate children under 5 years of age, that gap will exist. In addition, this winter season will be important to know whether we are already endemic or not. It will be the key point and it will determine if we will have a peak or not in the summer.
“In the case of the rest of the diseases, we need to correct what has been deficient in different governments, and we are going to have the resurgence of other infectious diseases that had already been forgotten. We have the example of poliomyelitis, the increase in meningeal tuberculosis, and we will have an increase in whooping cough and pertussis-like syndrome. In this sense, we are going back to the point where Mexico and the world were around the ’60s and ’70s, and we have to be very alert to detect, isolate, and revaccinate.”
Finally, Comas called for continuing precautionary measures before the arrival of the sixth wave. “At a national level, the sixth wave of COVID-19 has already begun, and an increase in cases is expected in January. Regarding vaccines, if you are over 18 years of age and have not had any vaccine dose, you can get Abdala, however, there are no studies on this vaccine as a booster, and it is not authorized by the Mexican government for this purpose. Therefore, it is necessary to continue with measures such as the use of face masks in crowded places or with poor ventilation, and in the event of having symptoms, avoid going out and encourage ventilation at work and schools. If we do this, at least in the case of diseases that are transmitted by the respiratory route, the impact will be minimal.”
Martínez Jiménez and Comas García have disclosed no relevant financial relationships.
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This article was translated from the Medscape Spanish Edition.
