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As cases of the new coronavirus continue to sweep across the nation, more is being learned about the populations for whom the infection is most dangerous and deadly.

While very few cases have been reported in infants, newborns are a population in which there is a unique form of risk — direct spread from an infected mother to the infant before birth, called “vertical transmission.” Additional data was released Monday suggesting vertical transmission may not occur, which may bring some relief to expectant mothers living through this pandemic.

Dr. Asim Ahmed, pediatric infectious diseases physician at Boston Children’s Hospital, notes that even small data is important to report. “People publishing even their observational data is key — that way you have an accruing aggregate of what the risk is,” he said.

Limited new data

To date, only two small studies have been published focusing on newborns born to mothers with confirmed COVID-19. Both of these reports, while drawn from limited data, provide evidence that vertical transmission of SARS-CoV-2 did not occur.

The first published study described nine mothers in their third (final) trimester who developed COVID-19 and gave birth to healthy infants via cesarean section. Not only did the babies test negative for coronavirus, but so did the mother’s breast milk and fluid that surrounds infants in the womb.

The most recent report of infants born to mothers with COVID-19 was released yesterday. Again, it suggests that infants may do well in spite of maternal illness.

The four infants described were born full term to mothers with COVID-19, immediately isolated, and fed formula. None of the infants developed fever or symptoms, including the only one of four that was not born via C-section. Although one family declined testing, the other three infants tested 72 hours after birth were negative for coronavirus. One infant did have some mild breathing difficulty early on, but this was diagnosed as a common newborn illness often seen in babies born via C-section (“transient tachypnea of the newborn”). Two had rashes that resolved on their own. All infants were discharged healthy with their mothers.

“The novelty is that there was one infant born via vaginal delivery who did not contract the virus. Obviously this was just one case and would need to be followed,” notes Ahmed. “In terms of guidance on what to do in terms of requirements for C-section, it’s too limited to make any statements about it.”

Drawing from similar virus outbreaks

While this coronavirus is a new strain, MERS and SARS are related coronaviruses from which researchers can learn. In both of these epidemics, there were also no documented cases of vertical transmission.

However, infections earlier in pregnancy did cause significant complications for offspring, including prematurity or smaller birth weight. It is too early to tell if this will be true for COVID-19.

Do infants remain safe after the newborn period?

Like newborns, older infants and children have infrequently been observed to have COVID-19. Even so, all released information has been encouraging.

According to the research released Monday, the largest to date focusing on infants and children, this population can be infected but generally have less severe symptoms than adults. Out of all 2,143 patients aged 1 day to 18 years with suspected or confirmed COVID-19, only one child died and most cases were mild. Almost 6% had severe symptoms, with more of these occurring in infants, but this is comparatively much less than the approximately 18% of adults that have severe illness.

It remains unclear why children generally have a milder illness. There is some speculation that it may be due to their immune systems or the receptor that scientists currently think is the target of the virus, but it is too early to be certain.

Can current and soon-to-be mothers rest easy now?

While expectant mothers and families may breathe a sigh of relief, Dr. Ahmed notes this data is extremely limited.

“The limited data is reassuring, but it’s observational and small. More studies, even observational, will be useful to clarify the risk.”

None of the reported mothers had severe symptoms requiring breathing support nor underlying health problems that would have otherwise placed them at risk for severe disease. Similarly, all infants were previously well and had no documented underlying disease. More importantly, it is still too early in this pandemic to provide evidence on mothers who were infected earlier in pregnancy.

Cautious optimism is key, Ahmed notes, and — as is true for most of what is known about this new disease — there remains very little data. “It’s difficult to know which way this will go. You also don’t want to be giving false hope.”

Social distancing is also important for infants

Equally important to remember is infants are clearly not immune from the disease. Babies may have mild or no symptoms, making them silent carriers of the virus able to infect vulnerable close contacts. Adult caregivers should take precautions, washing hands frequently, sterilizing toys, and disinfecting household items. Infants may not lead much of a social life, but should be practicing social distancing along with the rest of society.

Dr. Ahmed stresses the need for population-wide social distancing. “While you may not be taking actions to specifically protect yourself or your kids, it’s really to save the vulnerable population that you may not be directly connected to. By the time you think it makes sense it’s too late.”

The future role of vaccines

Dr. Ahmed thinks there is another subplot specific to children that’s been lost in discussions on this pandemic. “If I were to tell you that there was a virus as (or more) dangerous that primarily affects kids and the only reason we don’t act this way is because we have a vaccine against it – and that virus is measles – that should highlight how important vaccines are.”

“If we already had a vaccine, we wouldn’t be doing this – all of this is in place of a vaccine,” he said.