A study in Vietnam suggests that giving children fewer doses of the pneumococcal conjugate vaccine (PCVs) is as effective as the current standard schedule of doses, potentially making vaccination programmes more affordable for low- and middle-income countries (LMICs).

The pneumococcal conjugate vaccine (PCV) helps protect against bacterial infections such as meningitis and pneumonia which are a major cause of illness and death for babies and children worldwide.

The World Health Organization (WHO) currently recommends three doses of PCV are given to children in early infancy. However, high costs of the PCV programme have been a significant barrier in implementing and maintaining the programme within low- and- middle-income countries (LMICs). As a consequence, there has been interest in PCV programmes with fewer vaccine doses.

The researchers involved in this study, from the London School of Hygiene & Tropical Medicine with partners in Vietnam, Nagasaki University and the Murdoch Children’s Research Institute, compared colonisation frequency of bacteria among children who received different numbers of doses.

The findings, published in the New England Journal of Medicine, suggest that a PCV schedule for infants of one primary dose and one booster dose could provide similar health benefits as programmes which administer two primary doses and one booster, or three primary doses.

The study was carried out between 2016 and 2020 in the city of Nha Trang in Vietnam, where PCV had not been used previously. The authors focus on whether reduced number of vaccines in PCV programmes can maintain herd immunity i.e. community-wide protection and prevent infections. Since the beginning of the trial, a reduced PCV programme has been introduced in the UK.

The results showed that giving one primary and one booster dose of PCV had a similar impact as providing more vaccine doses in controlling the carriage of Streptococcus pneumoniae – the bacterium responsible for pneumococcal diseases like meningitis and pneumonia.

Carriage is when the bacteria colonise an individual’s nasopharynx (the top of the throat). Although this doesn’t cause symptoms, it creates a reservoir that can cause pneumococcal disease and spread infections to other people. Measuring changes in carriage is, therefore, an important indicator of how the disease burden may change at a community level.

As noted in the publication, concerns have been raised about whether PCV programmes are financially sustainable for LMICs that transition out of support from Gavi, the Vaccine Alliance, for vaccine costs.

The researchers hope that these findings can inform future vaccination policies and programs. In particular, they hope it helps make PCV programmes more financially feasible for LMICs who have successfully controlled pneumococcal bacteria with their current programmes and can now shift to vaccine programmes to maintain community-wide protection against pneumococcal transmission and disease.

Stefan Flasche, Professor of Vaccine Epidemiology at LSHTM, said: “We were pleased to find that our hypothesis from 10 years ago was true and that this trial could add to the growing evidence base on options for more cost-effective pneumococcal conjugate vaccine (PCV) use in settings with high vaccine coverage.”

Billy Quilty, Postdoctoral Researcher at Charité - Universitätsmedizin Berlin, said: “The use of pneumococcal conjugate vaccines (PCVs) has been incredibly successful in reducing the burden of pneumonia and other pneumococcal diseases, yet PCV remains one of the most expensive vaccines in a country’s infant immunisation programme.

“This trial provides evidence that in countries with mature PCV programmes, control of carriage can be maintained with fewer doses given, ensuring the sustainability of PCV programmes into the future.”

Kevin van Zandvoort, Research Fellow at LSHTM, said: “Controlling pneumococcal carriage, and therefore pneumococcal disease, through fewer PCV doses can reduce the costs for national immunization programmes and may make PCVs accessible in settings where it is not feasible to deliver multiple PCV doses such as in certain humanitarian crises.”

Publication:

Yoshida, L-M. et al. Effect of a Reduced PCV10 Dose Schedule on Pneumococcal Carriage in Vietnam. New England Journal of Medicine. DOI: 10.1056/NEJMoa2400007