Abstract
Vaccination is one of the most cost-effective successful public health interventions. Maternal vaccination protects both mother and baby from the morbidity of certain preventable diseases.
Introduction
Vaccination is one of the most cost-effective successful public health interventions. Maternal vaccination protects both mother and baby from the morbidity of certain preventable diseases.
Basics of Immunology
Immune response is the ability of the body to identify, recognise and defend against harmful toxins, infections or disease by making specific antibodies or sensitised white blood cells.1, 2
The different antibodies produced by plasma cells as classified by isotype are five major isotypes (IgA, IgD, IgE, IgG and IgM).3
Immunity is produced by one of two body reactions:
1. Active immunity is the ability to produce immunity either by exposure to the disease, infection, organism or by vaccination (killed or weakened form of organism).4 The protection is provided by a person’s own immune system, is natural and often lasts for life.
2. Passive immunity involves administration of immunoglobulins which provides a quick but short-term immunity that wanes with time. These include varicella zoster hepatitis B immunoglobulin or transplacental transfer of antibodies from the mother.
Vaccination
Vaccination stimulates immune response against a specific antigen and provides protection from contracting the disease by forming antibodies.5
Types of Vaccines
1 Live Attenuated Vaccines
These vaccines contain pathogens, which have been weakened to diminish their infectivity and pathogenicity by repeated culturing. They do not cause illness, but retain their ability to replicate and stimulate production of antibodies. The immune response is virtually identical to the naturally produced long-term immunity with one dose, except oral vaccines which need repeating.6
Side effects of live vaccines are:
The organisms might revert to a virulent form resulting in infection although of milder form
Contraindicated in pregnancy as they have the potential to infect the fetus
In immunocompromised individuals they cause uncontrolled replication of organisms, which may cause fatal reaction
Vaccine can become ineffective by heat, light, presence of antibodies from other sources (transplacental or blood transfusion)6
Examples of a live attenuated vaccine are measles–mumps–rubella vaccine (MMR combined vaccine), varicella, measles, rotavirus, smallpox, chickenpox, yellow fever or the antibacterial vaccines, Bacillus Calmette-Guérin (BCG) vaccine and oral polio vaccine.
2 Live Inactivated Vaccines
These vaccines are produced by growing bacteria or the virus in culture media and then inactivating it with heat or chemicals. They are not alive and cannot replicate, and are therefore unable to cause disease even in an immune-deficient person.
Unlike live vaccines, these are not affected by circulating antibodies and hence can be given when antibodies are present in the blood, e.g. in infancy or following receipt of antibody-containing blood products. They require multiple doses. The first dose only primes the immune system. A protective immune response develops after the second or third dose.
Antibody titres diminish with time and, as a result, may require to be boosted with periodic supplemental doses.
Examples of inactivated vaccines: hepatitis A, flu, polio, rabies.
3 Recombinant Vaccines
Recombinant vaccines are produced by genetic engineering technology. Currently eight such vaccines are available:
1. Hepatitis B vaccine
2. HPV (human papillomavirus) vaccine
3. Live typhoid vaccine
4. Live attenuated influenza vaccine (LAIV)
5. Whooping cough (part of the diphtheria, tetanus and pertussis (DTaP) combined vaccine)
6. Pneumococcal vaccine
7. Meningococcal vaccine
8. Shingles vaccine
Vaccination in Pregnancy
Vaccination during pregnancy is not a routine event, and attenuated live virus vaccinations are generally contraindicated. A woman should be up to date with her routine immunisation before pregnancy against preventable diseases.
Vaccination during pregnancy is warranted when:
1. The risk of exposure is high
2. Infection poses risk to mother/fetus
3. Vaccine is unlikely to be harmful
The benefits to mother and fetus should outweigh the risk of vaccination. It is preferable to delay immunisation until the second trimester to avoid the period of organogenesis unless medically indicated; however, no evidence exists of risk to fetus from inactivated vaccines or toxoids.7, 8 [evidence levels EL 2 & 3]
In the clinical context, vaccines can be broadly divided into three groups.
1. Vaccines contraindicated during pregnancy: live attenuated vaccines could cross the placenta and result in viral infection of the fetus, e.g. MMR and the varicella vaccines.
2. Vaccinations specially recommended during pregnancy, e.g. the trivalent inactivated influenza vaccine during the influenza season.
3. Vaccinations recommended for women at risk of exposure (hepatitis B).8
Rubella
Vaccine against rubella is routinely given to all as part of childhood immunisation, and 97 per cent of women in the UK are immune.
Rubella vaccine is contraindicated during pregnancy as it is presumed to cause fetal anomalies; however, if the vaccine is inadvertently administered to a pregnant woman, or pregnancy occurs within 28 days of vaccination, it should not be the reason for termination of pregnancy. She should be counselled about the theoretical risks to the fetus and the need for close follow-up.9
At the preconception counselling, a non-immune woman (immunoglobin (IgG) levels <10 IU/mL) should be offered MMR vaccine as a single dose and counselled to avoid pregnancy for 28 days after vaccination.
A pregnant non-immune woman should be offered vaccination during the postpartum period even if she is breastfeeding. Rubella virus is secreted in breastmilk; seroconversion without serious infection is reported in breastfed infants.
Varicella Zoster (VZV)
Approximately 90 per cent of women are immune because of childhood vaccination or exposure.
Universal screening to check immune status is not recommended; however, in certain situations the immune status should be checked.10
1. Women with an uncertain or no previous chickenpox infection
2. Those who come from tropical or subtropical countries
3. Those who had an exposure to the infection
Varicella vaccine contains live attenuated virus derived from the Oka strain of VZV and is contraindicated in pregnancy due to theoretical risks of fetal infection.
If a woman is sero-negative, she should be offered postpartum immunisation of two separate doses four to eight weeks apart and advised to avoid pregnancy for four weeks after the second dose. She should be reassured about its safety during breastfeeding.
Women are advised to avoid contact with chickenpox or shingles and to inform a health care worker in case of significant contact. Contact with pregnant women should be avoided if a post-vaccination rash occurs. [EL 2]
If the pregnant woman is not immune to VZV and she has had a significant exposure, she should be offered varicella zoster immunoglobulin (VZIG) as soon as possible.10
Inadvertent exposure to vaccine in pregnancy is not an indication for termination as there has been no increase in the risk of fetal abnormality above the background risk.
A review of the Pregnancy Registry for VARIVAX following 362 pregnancies inadvertently exposed to varicella vaccine showed there was no case of congenital varicella syndrome and no abnormal features or birth defects in the infants. [EL 2]
Whooping Cough (Pertussis)
This is an acute bacterial infection. It is highly contagious, caused by Bordetella pertussis spreading through droplets (coughing and sneezing).
Vaccinating pregnant women against whooping cough has been highly effective in protecting newborn babies. It offers immediate protection to cover the newborn until they can have their first vaccination at two months of age.
Babies born to women vaccinated at least a week before birth had a 91 per cent reduced risk of becoming ill with whooping cough in their first weeks of life, compared with babies whose mothers were not vaccinated.11
In 2012, the UK experienced a nationwide epidemic of pertussis, resulting in serious complications (pneumonia, encephalitis, seizures, brain damage) including death, especially in young babies. A programme for the vaccination of pregnant women between 28 and 32 weeks against pertussis was introduced in October 2012.11
However, it can be given at any time until the start of labour, although after 38 weeks the fetus is less likely to be protected by maternal immunity.
The Joint Committee on Vaccination and Immunisation (JCVI) of the Royal College of Obstetricians and Gynaecologists (RCOG) recommended that from April 2016 the vaccination should be offered from 20 weeks (after the anomaly scan).12
Many countries including the United States, Spain, Australia, New Zealand, Belgium and Argentina currently recommend vaccination against whooping cough in pregnancy.
Pregnant women need to be vaccinated even if they have been vaccinated in childhood or in a previous pregnancy. Both randomised clinical trials and cohort studies support its safety (no increase in pregnancy complications, preterm birth, low birthweight, congenital anomalies, spontaneous abortion, or stillbirth).13 [EL 1]
Vaccination of the close contacts of the neonate (mother’s partner) is recommended as a strategy for newborn prevention, when the mother has not been timely vaccinated.13
Tetanus
Worldwide, each year, tetanus kills an estimated 180 000 neonates (about 5 per cent of all neonatal deaths, 2002 data) and up to 30 000 women (about 5 per cent of all maternal deaths).
Tetanus vaccine is a toxoid vaccine and protects against both maternal and neonatal tetanus.
All pregnant women should receive a tetanus toxoid vaccine during each pregnancy, irrespective of any previous history of immunisation.
The optimum time for passive antibody transfer is from the 27th until the 36th week. A booster dose is indicated if a pregnant woman is exposed to the risk of tetanus infection during or immediately after delivery.
Diphtheria
Diphtheria can lead to breathing problems, heart failure, paralysis and death. The Tdap vaccine has a dose of tetanus toxoid, reduced diphtheria toxoid and acellular pertussis.
All pregnant women should get a Tdap vaccination in each pregnancy.
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