Maternal immunization

# Overview
Immunization prevents illness, disability, and death from vaccine-preventable diseases. Vaccines are useful in reducing childhood mortality and morbidity. The standard vaccination schedule starts at early infancy and is not complete by the age of 6 months. Therefore, most children do not have immunological protection during the period of early infancy, which may predispose them to infections. This gap may result in higher infection-related hospitalization and disease complications in early infancy than in older children. Maternal vaccination has entered consideration as a potential means of closing this gap. While maternal vaccination can protect an expectant mother from acquiring infection, it is also effective for infant protection.

# Immunology
Maternal immunity changes during pregnancy, under influence of pregnancy-associated hormonal changes. Increased levels of estrogen and progesterone are the most important factors for these changes. Increased levels of estradiol are associated with increased levels of the body's T-helper type 2 cell response, compared to type 1 T-cells. However, increased levels of progesterone may result in a decrease in the robustness of the immune response and an alteration in the function of the immune system. Other aspects of the immune response, such as phagocytosis and the number of neutrophils and monocytes, remain unchanged. These changes (alterations in cell-mediated immunity) are to blame for sub-optimal immune responses to certain viral infections (e.g., influenza). Furthermore, this accounts for the need for immunization against these infections in pregnant women. Other pathways within the immune system remain intact during pregnancy; immunosuppression does not occur as a result of pregnancy. The clinical effectiveness of vaccination during pregnancy is maintained, as changes in the immune balance do not influence their effectiveness.

# Maternal immunization recommendation
Inactivated influenza and combined tetanus-diphteria-acellular pertussis (TDaP) vaccines are recommended for pregnant women in the U.S. Hepatitis B and hepatitis E vaccines are recommended in some other countries.
The following table summarizes available vaccines and current recommendations for their administration during pregnancy.

## Influenza vaccine
Administration of the influenza vaccine is now recommended for all pregnant women (during each pregnancy). The vaccine can be administered in any trimester of pregnancy because influenza causes more consequences in pregnant women than those who are not pregnant. Furthermore, infants under 6 months of age are at the greatest risk of complications and death associated with influenza. Influenza infection is associated with an increased risk of subsequent bacterial infection. particularly pneumococcal infection and disease. This potential risk can be leveraged from early infancy by maternal immunization with influenza vaccine.

## Pertussis vaccine
The reason for pertussis vaccination in pregnancy is to prevent infants from developing pertussis. TDaP is the prescribed vaccine for this purpose. Current recommendations allow for administration of the pertussis vaccination during any trimester of pregnancy, though with a preference for administration late in a pregnancy: a gestational age of 27 to 36 weeks in the United States and 20 to 32 weeks in the United Kingdom.

# Future perspective
Recently, there have been increasing efforts to develop new vaccines for pregnant women. Respiratory syncytial virus (RSV) and group B streptococcus have been areas of great progress recently.

## Respiratory Syncytial Virus Vaccine
Due to the high mortality associated with RSV infection in early infancy, it is important to develop a vaccine against it that can prevent this infection in newborns. RSV is the leading cause of viral acute lower respiratory tract illness, and the highest associated morbidity is found among preterm infants. 2 to 3% of all neonatal deaths in the United States can be attributed to RSV. Vaccines in early and preclinical development include live attenuated, whole inactivated, particle-based, subunit, nucleic acid, and gene-based vector vaccines. However, they are still in developing stages and have not been approved for clinical use.

## Group B Streptococcal Vaccine
Group B streptococcus is cosidered a potential threat in early infancy. It may cause serious illnesses, especially in preterm infants, including: sepsis, pneumonia, and meningitis. Group B streptococcus may also result in stillbirth. The most important means of transmission is from the birth canal during delivery (i.e., vertical transmission). A maternal group B streptococcal vaccine could help prevent infection in early infancy. Recently, monovalent and trivalent conjugate vaccine candidates have been evaluated in clinical trials awaiting results and approval.

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