Monday, February 14, 2022

COVID-19 vaccination in pregnancy may protect infants

 Jennifer Middleton, MD, MPH

COVID-19 vaccination is safe and beneficial in pregnant persons, a group that is especially vulnerable to complications from COVID-19 infection. Emerging research now suggests that these protections may extend to infants through at least the first 6 months of life. Building on earlier studies that demonstrated COVID-19 antibody transmission from mother to infant in utero and in breastmilk, a small study found antibodies against the SARS-CoV-2 spike protein persisted in infants whose mothers received COVID-19 vaccination in pregnancy. 

Researchers at Massachusetts General Hospital followed pregnant persons from their 2nd trimester who either received COVID-19 vaccination or had COVID-19 infection between weeks 20-32 of pregnancy. They chose this time frame because "previous studies have demonstrated superior transplacental transfer of antibodies during this window compared with vaccination closer to delivery." They then measured antibodies against the SARS-CoV-2 spike protein in the enrolled participants' infants for their first 6 months of life. 77 pregnant persons who received COVID-19 vaccination and 12 pregnant persons with symptomatic, documented COVID-19 infection were included in the study:

Vaccinated mothers had significantly higher titers at delivery with a mean (SD) of 2.03 (0.47) optical density (OD450-570) compared with mothers after infection with a mean (SD) of 0.65 (0.76) OD450-570 (P < .001)....Vaccination resulted in significantly greater antibody persistence in infants than infection. At 6 months, 57% (16 of 28) of infants born to vaccinated mothers had detectable antibodies compared with 8% (1 of 12) of infants born to infected mothers (P = .005). 

This study's findings suggest that "natural" immunity from disease is not superior, and may be inferior, to immunity induced by vaccination, though it's important to note that titer levels are a disease-oriented evidence (DOE) outcome. There is no evidence yet that COVID-19 vaccination in pregnancy reduces infants' risk of illness or hospitalization (POEM-level outcomes) compared to COVID-19 infection in pregnancy. Given that other established vaccines have demonstrated a link between infant titers and disease protection, however, this study offers hope that maternal COVID-19 vaccination may offer some protection to infants. 

Protecting infants is important despite conventional wisdom that COVID-19 infection is less severe in children than in adults. Infants appear to be at the highest risk of complications from COVID-19 among children under the age of 18 years. A study from China early in the pandemic (before vaccines were available), found that the prevalence of "severe" or "critical" COVID-19 complications in children under the age of 1 year was 8.8% and 1.9%, respectively. This information is important to share with pregnant persons and parents; yes, overall children have a lower risk of complications from COVID-19 infection, but infants have the highest risk among children under the age of 18 years.

No ongoing or planned COVID-19 vaccination trials include infants under the age of 6 months, so maternal vaccination - along with vaccination of all household members and close contacts - will likely be critical to protecting this age group from COVID-19 infection and its potential complications. Future studies are needed to establish maternal vaccination's benefit for preventing infections, hospitalization, and mortality in infants, but this newest study may inspire future research to answer those questions. In the meantime, we should continue to advise pregnant persons to receive COVID-19 vaccination, and perhaps the potential of benefit for their infant may sway some vaccine-hesitant individuals toward vaccination.

If you'd like to read more, the AFP By Topic on COVID-19 continues to be regularly updated, and this AFP editorial reviewing "Strategies for Addressing and Overcoming Vaccine Hesitancy" has many useful tips.