As awful as COVID19 has been over the last year and a half one thing has continued to perplex myself and others. Why do babies whethe term or preterm so rarely acquire the virus? Numerous studies have been able to document placental changes and infection of these tissues. On rare occasions reports have come out with evidence of neonatal infection but fortunately most are mild.
These findings have in large part contributed to the Canadian Pediatric Society practice points on three topics.
Why might babies be so resistant?
The first post on this topic was entitled What’s in your nose makes you more or less susceptible to COVID19
In this post an argument was made that the reason these infants are resistant is due to low levels of ACE-2 receptors in the nasal mucosa of children. In this study children as young as 4 years of age were found to have very low levels of this receptor (portal of entry for SARS-CoV-2) into the host. I speculated at the time that if one carried forward the findings to younger children and infants you might find there were hardly any receptors at all.
Well, someone finally did the study and confirmed what I suspected. The study report is entitled Nasal expression of SARS-CoV-2 entry receptors in newborns by Heinonen S et al. It’s not a big study but the results are consistent across 28 newborns (17 term and 11 preterm) and 10 adults. In each newborn whether term or preterm a nasal mucosal scraping was performed at 24 hours of age and used to measure by reverse-transcription quantitative PCR mRNA expression of ACE2, transmembrane serine protease 2 (TMPRSS2), neuropilin 1 (NRP1) and neuropilin 2 (NRP2) and insulin-like growth factor 1 receptor (IGF1R).
What the results show you is that babies are not just small adults. They are different yet preterm do not seem to be that different than term infants in terms of receptors. While ACE2 has garnered most of the attention when it comes to receptors for SARS-CoV-2 the others also play a role and are in general expressed to a lesser degree in neonates than adults.
In the previous post I argued what was in your nose makes a difference to your risk of contracting SARS-CoV-2. Really the point is what is not in your nose. Thankfully neonates do not have good expression of these receptors and that may be the biggest reason for the general protection they have from this pandemic. It has certainly a good time to be in the “have not” group!