This paper summarises the data available on both maternal and neonatal vaccination to prevent disease in newborns and early infancy and considers the key challenges and next steps for research in the field.
The last decade has witnessed important reductions in under-five mortality thanks to vaccine intervention. Consequently, as we move into the new post- 2015 sustainable development agenda, child survival strategies that aim to reduce mortality in early infancy in low- and middle-income countries, have some of the greatest potential for life-saving impact.

The pneumococcal vaccine field has continued to evolve since the PCVs were licensed and first introduced into routine infant immunisation schedules. Initial introduction in high-income countries has now been followed by routine use in many low- and middle-income countries, thanks to WHO endorsement and GAVI purchasing with 126 countries using PCV to date. Geographical differences in pneumococcal epidemiology, dominant carriage and disease-causing serotypes, and prevalence of nasopharyngeal carriage in different age groups have meant that the impact of PCV in diverse settings has not been uniform.

Contributing factors to diverse outcomes have included the presence of a catch-up campaign targeting children too old to have been vaccinated according to the routine schedule, largely implemented only in high-income countries. Different vaccination schedules, including two or three infant priming doses with or without a booster dose, have also been used and variable levels of vaccine coverage within the target age groups have been achieved. All of these factors have complicated the analysis of optimal strategies for PCV introduction and maintenance of control of VT disease. Consequently, a significant volume of work both in the form of clinical trials and post-introduction disease surveillance continues.

Indirect protection has played an important role in the demonstrated effectiveness of the PCVs so far and has impacted on disease, not only in older children and adults, but also in infants too young to have been vaccinated. Such effects have predominantly been seen in high-income countries where PCV coverage has been high, a booster dose of PCV in the second year of life has been used, and where carriage is relatively low and largely confined to infants less than 5 years of age.

Five-year view
Trials underway or planned are expected to provide definitive safety data on maternal pneumococcal conjugate vaccination and further strengthen the existing data set related to newborn vaccination, although the safety profile of the latter is already supportive.

Thus, within 5 years, new questions related to the role of maternal and newborn pneumococcal vaccination are also likely to have been generated while existing questions are addressed.It is hoped that the next 5 years will bring significant progress in this area which could also impact on the questions related to maternal and neonatal pneumococcal vaccination.

Within the next 5 years, the potential utility of both maternal and newborn pneumococcal conjugate vaccination is likely to become much clearer.The level of indirect protection from infant immunisation delivered according to the EPI schedule in low-income, high-carriage settings over the initial months of life is likely to be established as programs become embedded.

Key issues
• Numerous trials of maternal vaccination with the 23-valent pneumococcal polysaccharide vaccines have been undertaken, but a recent systemic review concluded that based on these trials there was insufficient evidence to determine a role for maternal pneumococcal vaccination in pregnancy.
• Further clinical trials are currently underway or being planned to examine both maternal and neonatal pneumococcal- conjugate vaccination in low-income settings.
• Due to differences in pneumococcal epidemiology, the indirect protection seen in newborns in high-income settings are unlikely to be translated consistently into low-income countries and residual disease in early life seems likely to persist in the absence of additional interventions.
• The 7-, 10- and 13-valent PCVs have been highly effective at preventing infection and carriage of the included pneumococcal serotypes in infants and children following their rollout in high-, middle- and low-income countries.

Authors
Ed Clarke, Beate Kampmann and David Goldblatt

Read more about the study on the Taylor & Francis online website
http://www.tandfonline.com/doi/full/10.1586/14760584.2016.1167602