ABSTRACT
Numerous COVID-19 vaccines are authorized globally. To date, [~]71% of doses are comprised of the Pfizer/BioNTech vaccine, and [~]17% the Moderna/NIH vaccine, both of which are mRNA-based. The chimpanzee Ad-based Oxford/AstraZeneca (AZ) vaccine comprises [~]9%, while the Johnson & Johnson/Janssen (J&J) human adenovirus (Ad26) vaccine ranks 4th at [~]2% [1]. No COVID-19 vaccines are yet available for children 0-4. One method to protect this population may be passive immunization via antibodies (Abs) provided in the milk of a lactating vaccinated person. Our early work [2] and other reports [3-5] have demonstrated that unlike the post-SARS-CoV-2 infection milk Ab profile, which is rich in specific secretory (s)IgA, the vaccine response is highly IgG-dominant. In this report, we present a comparative assessment of the milk Ab response elicited by Pfizer, Moderna, J&J, and AZ vaccines. This analysis revealed 86% -100% of mRNA vaccine recipient milk exhibited Spike-specific IgG endpoint titers, which were 12 - 28-fold higher than those measured for Ad vaccine recipient milk. Ad-based vaccines elicited Spike-specific milk IgG in only 33%-38% of recipients. Specific IgA was measured in 52%-71% of mRNA vaccine recipient milk and 17%-23% of Ad vaccine recipient milk. J&J recipient milk exhibited significantly lower IgA than Moderna recipients, and AZ recipients exhibited significantly lower IgA titers than Moderna and Pfizer. <50% of milk of any group exhibited specific secretory Ab, with Moderna recipient IgA titers measuring significantly higher than AZ. Moderna appeared to most frequently elicit >2-fold increases in specific secretory Ab titer relative to pre-vaccine sample. These data indicate that current Ad-based COVID-19 vaccines poorly elicit Spike-specific Ab in milk compared to mRNA-based vaccines and that mRNA vaccines are preferred for immunizing the lactating population. This study highlights the need to design vaccines better aimed at eliciting an optimal milk Ab response.
ABSTRACT
The Pfizer/BioNTech and Moderna mRNA-based COVID-19 vaccines are licensed under emergency use authorization, with millions of doses already administered globally [1]. No COVID-19 vaccines are yet under investigation for use in infants or young children. As such, the passive immunity of the antibodies (Abs) provided through milk from a vaccinated person may be one of the only ways to protect this population until pediatric COVID-19 vaccines are licensed. Our early work (as well as an expanded study being published concurrently with this report) examining the milk Ab response after SARS-CoV-2 infection demonstrated that Spike-specific IgA in milk after infection is dominant and highly correlated with a secretory Ab response [2]. Determining if secretory Abs are elicited in milk is critical, as this Ab class is highly stable and resistant to enzymatic degradation in all mucosae - not only in the infant oral/nasal cavity and gut, but in the airways and GI tract as well [3, 4]. Presently, we describe our analysis of the milk Ab response 14 days after completion of an mRNA-based COVID-19 vaccine regimen among 10 individuals. It was evident that unlike the post-infection milk Ab profile, IgG dominates after COVID-19 vaccination. One hundred percent of post-vaccine milk contained significant levels of Spike-specific IgG, with 8/10 samples exhibiting high IgG endpoint titers. Conversely, 6/10 (60%) of post-vaccine samples were positive for Spike specific IgA, with only 1 (10%) exhibiting high IgA endpoint titer. Furthermore, 5/10 (50%) post-vaccine milk samples contained Spike-specific secretory Ab, none of which were found to be high-titer. As our analyses of the immune response in milk to COVID-19 vaccination continues, it will provide a critical opportunity to address huge knowledge gaps, inform the field as to which COVID-19 vaccine, if any, is likely to provide the best milk Ab response, and highlight the need to design improved vaccines with protection of the breastfeeding infant in mind.
