COVID-19 pandemic: Children have a magic shield?
Since COVID-19 came, life has changed significantly regardless of our daily needs. Around 90% of working parents hit hardly by the pandemic COVID-19 because of the changes of routine. Schools, daycare centers are closed to reduce the transmission of virus through children. Although offices are closed andno need to be at work-place physically, work from home came in effect immediately for many of the families. Taking care of kids at home and attending their remote classes, to provide support seem to be the most essential job now. Parents perhaps started nagging at children more often than before COVID-19 hits. Nagging is counterproductive because repeated nagging trains kids stop listening parents. Children are complete human 'beings' not human 'becomings'.
While speaking about the virus transmission, children could be a good carrier as the nature of this virus is highly replicating and might be easily transmitted to the community. Although children are always considered as the most vulnerable group compared with adults, COVID-19 infection in children seems to be less severe and not as a big life-threatening as it shows in the elder group of people. Some COVID-19 related complications have been reported in children under 18 years old recently.
It is probably too early to say anything about this virus with respect to pathogenesis outcomes in children. One thing for sure under the limited access of diagnosis which is primarily given to symptomatic patients, children whether exposed to the virus or not are not displaying symptoms that would attract health professional attention immediately. One of the silver linings of the coronavirus pandemic is that it seems to spare children and there are numbers of theories behind this-
1. Children generally develop cold-like symptoms throughout the year after being exposed to several common cold causing pathogens. This repeated exposure perhaps make their immune system active and well-armed to fight against COVID-19?
2. Effect of relatively fresh memory due to recent vaccination program, as children usually receive multiple routine vaccines and it is possible to have their frontline immune system ready to expel any specific and non-specific foreign invaders?
3. Generally magnitude of immune responses in children are lower than adults which also suggests that children are not prone to develop excessive immune reaction against COVID-19 while fighting off the pathogen?
4. COVID-19 binding to the host cell angiotensin-converting enzyme 2 (ACE2) and internalization of the complex is a requirement in the process of establishing infection. In children, however, either differential expression or shedding of ACE2 might play an important role against COVID-19 binding and invasion. This is still a key question in relation to less severe COVID-19 outcome in children.
There are number of recent studies with COVID-19 patients in different countries primarily focused on virus transmission and disease severity. Those studies included different age group of patients with COVID-19 infection. One German study analyzed the viral load based on the PCR data from different age-group of patients and found lowest viral count in youngest children and highest viral count in oldest group of patients. 43,000 for those aged 1-10 years, 63,000 for 11-20 years, 183,000 for 21-30 years and 164,000 for 31-40 years of age.
Interestingly, lower viral count was also noted in children with underlying diseases. This is one of the fascinating observations that overwhelmingly pointing the little kids that by any mechanism of immune reaction they had better control of COVID-19 than adults. Therefore, it is probably due to one or more of the above mentioned reasons why children are likely the safest group in this current pandemic.
How much we know about the children immune system?
Immune system begins to develop as early as in the fetal stage and keep preparing as time goes on. With a great help from maternal immunity new born baby is fully covered first several months before receiving routine vaccination. Large number of studies in the literature demonstrated that neonatal or children immune responses are not robust when compared with adults. This is perhaps due to the fact that neonatal or children immune system is still developing and learning against all known and unknown pathogens. Many immune cell compartment are not yet fully matured and functional.
However, there are studies also shown that neonatal immune response could also be strong, especially when vaccines are given with strong adjuvant that potentially helps immune cells to react to a foreign antigen. One good example is the BCG vaccine, which induces strong immune responses in neonates during the first couple of months. There are also examples that shows children immune response to certain pathogen is more tolerized. This means magnitude of responses is relatively low. For example, studies on H. pylori-infected children and adults have shown that children display less inflammation that adults even with the same level of H. pylori colonization.
Children are more capable of down regulating inflammatory responses than adults. Thus, there are some striking differences between children and adults in terms of increasing immune responses against same pathogen. In the same way, both children and adults also have evolved disparate regulation of controlling excessive immune responses. Uncontrolled immune responses could drive immune pathology and to this end effective inhibitory mechanisms play important role to limit tissue pathology.
Responses against COVID-19 in children:
There are only a handful of studies conducted in children due to lower number of cases since the COVID-19 outbreak noticed. One Chinese study compiled data from 24 articles to analyze immune cell numbers in children positive with COVID-19 (2597 cases) and compared with adults COVID-19 patients. COVID-19 infection in adults clearly showed decrease in immune cell numbers and surprisingly the effect in children was either minimal or not seen. However, further investigation in children showed some of the biomarkers elevated due to COVID19 as an indication of heart injury.
Those biomarkers were normal in adult patients. Interesting observation was also seen in mouse model of COVID19 infection. Younger mice survived well with the COVID19 challenge whereas adult mice succumb to infection. It is too early to pinpoint exact immune cells that are responsible to protect children from COVID19. However, based on the studies that designed to compare younger and older population in terms of their immune cell function, it is evident that older people do have less immune cell activity than younger people.
Both T and B cell are quite important to fight against this virus and perhaps children lung immune responses are well prepared for that. There are few key articles already demonstrated both T and B cell responses against COVID-19 in human who recently recovered from COVID-19 infection. Similarly, animals with COVID-19 primary infection seem to be protected from a secondary virus challenge and correlated with increased T and B cell responses.
Therefore, it can be a hope for the younger group in this crisis where immune system might be working as a frontline first responder against COVID-19 and providing a good care of children. When the true players of the immune system will be known, it would help in evaluation of new vaccine efficacy and ultimately a great relief for everyone.
Dr Jubayer Rahman writes from