Several cases of neonates infected by SARS-CoV-2 are reported in the literature and here we have systematically analyzed and synthesized them. Our findings confirm that SARS-CoV-2 can infect neonates and that the majority of these infections occur postnatally, although vertical transmission may be possible in about one third of cases. Neonatal SARS-CoV-2 become clinically evident in half of the patients as they developed features of COVID-19. The clinical appearance of neonatal COVID-19 seems similar to those reported in older patients, both in terms of symptoms and laboratory or imaging abnormalities, and the outcome was generally favorable. Neonates who were not transiently separated from their mothers seem to have a higher incidence of SARS-CoV-2 infections occurring after the first 72 hours of life.
These findings are important as they formally describe neonatal SARS-CoV-2 infection and partially fill our aforementioned knowledge gap. There are some interesting points to be highlighted. First, transplacental transmission of SARS-CoV-2 is indeed possible and this is corroborated by a consistent background of laboratory findings, since angiotensin-converting enzyme receptors are expressed in placental tissues, with the expression reaching a peak at the end of gestation, 72 and SARS-CoV-2 may invade the placenta 6,7 potentially causing miscarriage.73 Second, neonatal COVID-19 manifestations seem similar to those observed in adults, while fever seems to be more frequent in COVID-19 than in common neonatal infections 74 and no cases of neonatal ARDS were evident.75 Third, the choice between rooming-in or mother-infant separation is an important one and the synthesis of available cases shows that the avoidance of separation may be associated with a higher risk of late onset neonatal SARS-CoV-2 infections. This is potentially important since neonatal SARS-CoV-2 infections are more commonly postnatal, through environmental exposure. There are wide differences on this matter between the clinical guidelines issued by scientific societies and authorities worldwide.76–78 Thus, we believe that correct and complete counselling should be given to families in order to allow a well-informed choice. This should factor in the benefits of mother-neonate bonding, the risk of neonatal infection and the higher maternal contagiousness during the symptomatic period.79 If rooming-in is chosen appropriate hygiene advices should be given to reduce the transmission risk. Breastfeeding does not seem to be associated with SARS-CoV-2 infections and this suggests that viral transmission through the milk, if any, should be rare. These findings seem to support the safety of expressed breast milk even during mother-neonate separation. However, since few studies have investigated this matter and have yielded conflicting results,32,80 larger studies are needed to clarify this issue.8
The results of this synthesis of neonatal SARS-CoV-2 infections are also consistent with a review performed in older children and adolescents from Asia: SARS-CoV-2 infection usually seems mild in pediatric patients presenting with same clinical features or laboratory and imaging abnormalities.5 The analyzed neonates had a quite more frequent need for NICU hospitalization compared to neonates of similar gestational age 81 and to older children.5 However, this may be influenced by many factors such as local setting, logistics and isolation policy, since the NICU could represent the only area to isolate infected babies; this should be avoided if NICU care is not actually needed, in order to avoid the shortage of NICU beds during the pandemic.82
Since a significant proportion of infections are asymptomatic, it has so far been hard to ascertain the disease burden on neonates and the possibility of transmission to healthcare providers. We shed some light on this, although our findings may change as soon as the pandemic progresses and new experience is accumulated. Meanwhile, it is suggested that evidence derived from case reports and case series is the best available and should be used to inform decision making until higher level of evidence is available.13
This work has limitations. Although the quality of the reviewed reports is intermediate-to-good, we should remember that uncontrolled case descriptions and their synthesis are at the bottom of the evidence pyramid.13 As this is a meta-analysis of mainly case series, the rating of the quality of evidence is 4, according to the JAMA-modified Oxford Centre for Evidence-based Medicine classification.[71] However, the Grading of Recommendations, Assessment, Development and Evaluation guidelines admit the decision-making process based on low-quality evidence in some particular circumstances and the pandemic surely represents an extraordinary situation. [83][82][83][82][81][80][72] The classification system for diagnosing maternal, fetal and neonatal SARS-CoV-2 infections may be cumbersome, as it requires consideration of clinical data and of the results of several virological tests: the relatively low number of confirmed infections may be due to the difficulty in obtaining the virological tests in various samples (placenta, amniotic fluid, blood, swabs).9 However, this represents so far the best tool available to correctly identify these infections for epidemiological and clinical purposes and it should be promoted. Furthermore, the classification may be adjusted, and a case can be re-classified, if its likelihood of infection changes, as more information becomes available. Similarly, the availability of new diagnostic tests may lead to changes in the diagnostic criteria. We cannot exclude that some of the clinical features presented by the analyzed cases were due to other concomitant disorders, as this level of detail is not attainable with a synthesis of published reports; however, the analyzed data are coherent and consistent with those from older COVID-19 patients. Finally, we have almost no information on neonatal COVID-19 therapies, as these will require more experience and it is unclear if the neonatal SARS-CoV-2 infection may have long-term consequences, as no follow-up studies have been performed so far.
In conclusion, the synthesis of uncontrolled cases of neonatal SARS-CoV-2 infection shows that infections mainly occur postnatally through environmental exposure, although nearly 30% of infections may be acquired vertically. Approximately half of infected neonates develop clinically apparent COVID-19, which is often characterized by febrile status and favorable outcome. Mother-neonate rooming-in is associated with a higher incidence of SARS-CoV-2 infections occurring after the first 72 hours of life.