Vaccines constitute the most important public health intervention in recent decades that has contributed to improving the quality of life of people, reducing maternal and infant mortality. Indeed, after the introduction of vaccines, the average age of life increased, from 29 years in the 19th century to 75 years today, and vaccines save between 2 and 3 million children worldwide each year.
Vaccination today has been extended to the pregnant population, being a public health policy in many countries, endorsed by the World Health Organization. Vaccination during gestation immunizes not only the mother but also the fetus, since it allows the placental transmission of high concentrations of protective antibodies. The mechanism by which vaccines work is based on the development of immunity expressed by immunoglobulin G in the mother, which is then transmitted to the fetus transplacentally through the syncytiotrophoblast through a process called transcytosis. The efficiency of transcytosis can be affected by the pregnancy itself, the Ig G subtype, or the presence of maternal infection. Late vaccination, that is, from 28 to 32 weeks is the opportune moment, since there will be a greater placental transfer of antibodies providing greater protection to the newborn. The 4 subtypes of Ig G that are transferred also differ in efficiency since it is known that Ig G type 1 is in higher concentration, therefore it will induce a greater immune response. This effectiveness is attenuated in IgG type 4, 3, 2 respectively.
At present, according to the working document: Field guide on maternal and neonatal immunization for Latin America and the Caribbean of the World Health Organization of 2017, the following vaccines are recommended during pregnancy: Triple vaccine against tetanus, diphtheria and pertussis, Influenza vaccine, Meningococcal vaccine, Hepatitis A and B vaccines Yellow fever vaccines (for yellow fever)
The first two of mandatory use in pregnancy and the last three only in case of epidemic or in case of travel to endemic areas. In general, inactivated vaccines are considered safe when administered during pregnancy and vaccines made with bacteria or viruses, live or attenuated, are contraindicated during pregnancy due to the hypothetical risk of perinatal infection, although there are currently no reported cases. Infection secondary to an attenuated vaccine is generally milder than natural infection and is classified as an adverse reaction.
Although there is opposition from some population groups about the application of the vaccine in pregnancy, it is necessary to emphasize that the benefit of immunization to pregnant women greatly outweighs the potential risk when the chances of exposure to a disease are high, as occurs currently in a pandemic scenario and specifically we refer to the influenza vaccine. This disease manifests itself in a torpid way in pregnant women, associated with heart failure, myocarditis, pneumonia, and in the fetus it produces intrauterine growth retardation and preterm delivery; conditions that could greatly aggravate the maternal-fetal health status if a concomitant viral infection by SARS CoV-2 occurs.
Pregnancy itself is an exclusion criterion for clinical trials evaluating the effectiveness and safety of vaccines; Therefore, it should not surprise us that in most of the tests that currently exist used to evaluate the vaccine against COVID-19, the pregnant population is not included; Many of these trials first hope to confirm the safety and effectiveness of vaccines in the non-pregnant population. The outlook for immunizations during future pregnancy is promising; Vaccines for streptococcus type B, respiratory syncytial virus, cytomegalovirus, etc, will surely be incorporated into the official immunization schedule of the countries; In this context, it is very important that health professionals recommend vaccination to pregnant women, as evidence shows that pregnant women are more likely to be vaccinated if the health professionals who care for them recommend it.
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