Vaccine response was higher in formula-fed infants compared to breastfed but not affected by lactoferrin or iron in a randomised controlled trial.

AIM: To examine how reduced iron content and added bovine lactoferrin in infant formula affect the antibody response following routine immunisation. METHODS: In this randomised controlled trial, 180 Swedish formula-fed infants received, from 6 weeks to 6 months of age, a 2 mg/L iron formula with (n = 72) or without (n = 72) bovine lactoferrin, or a control formula with 8 mg/L iron and no lactoferrin (n = 36). Another 72 infants were recruited as a breastfed reference. Serum immunoglobulin G (IgG) levels against Haemophilus influenzae type b (Hib), diphtheria and tetanus were assessed at four, six and 12 months of age. RESULTS: With an equal gender distribution, 180 + 72 term infants were included with a mean age of 7.0 ± 0.7 weeks. At 12 months, infants fed low iron formula showed a significantly higher geometric mean Hib IgG (1.40 µg/mL [1.07-1.83]) compared to the control formula infants (0.67 µg/mL [0.42-1.07]). For all three vaccines, breastfed infants had significantly lower IgG levels at six and 12 months of age. CONCLUSION: Except for higher Hib IgG levels at 12 months in infants fed low iron formula, the interventions did not affect vaccine IgG response. Unexpectedly, breastfed infants had significantly lower vaccine IgG levels compared to formula-fed infants.

Hybrid Immunity Improves the Immune Response after the Fourth COVID-19 Vaccine Dose in Individuals with Medical Conditions Predisposing to Severe COVID-19.

Data on immune responses following COVID-19 booster vaccinations and subsequent infections in the immunocompromised are limited. We studied antibody responses after the fourth dose and subsequent infections to define patient groups benefiting most from boosters. Fourth vaccine (booster) doses were, in Finland, first recommended for severely immunocompromised individuals, whom we invited to participate in our study in 2022. We assessed spike protein-specific IgG and neutralizing antibodies (NAb) against the ancestral and Omicron BA.1 strains one month after the fourth dose from 488 adult participants and compared them to the levels of 35 healthy controls after three doses. We used Bayesian generalized linear modeling to assess factors explaining antibody levels and assessed vaccine-induced and hybrid immunity six months after the last vaccine dose. Chronic kidney disease (CKD) and immunosuppressive therapy (IT) were identified as factors explaining sub-optimal antibody responses. The proportion of participants with a normal antibody response and NAbs was significantly lower regarding CKD patients compared to the controls. By the 6-month sampling point, one-third of the participants became infected (documented by serology and/or molecular tests), which notably enhanced antibody levels in most immunocompromised participants. Impaired antibody responses, especially NAbs against the Omicron lineage, suggest limited protection in individuals with CKD and highlight the need for alternative pharmaceutical preventive strategies. Vaccination strategies should take into account the development of robust hybrid immunity responses also among the immunocompromised.