The Most Dangerous Germs Without Effective Vaccines

The World Health Organization has put out a hit list of germs for future vaccines to tackle. In a report published this week, WHO scientists have identified 17 widely common pathogens that most need new or improved vaccines, including influenza, HIV, norovirus, and Staphylococcus aureus bacteria.

Vaccines have long been one of humanity’s most important public health accomplishments, helping control or even eradicate fearsome diseases like smallpox, polio, and most recently covid-19. But we still don’t have vaccines for many widespread diseases out there, while some current vaccines are only modestly effective against their target germ, like the seasonal flu shot. There’s only so much time and resources that can be devoted to developing vaccines, though, so researchers at the World Health Organization have compiled a list of priority germs that especially need to be taken down a peg.

The researchers first consulted with international and local experts to establish criteria for their selections. These included factors such as the annual deaths of children under five caused by a disease or the extent of a germ’s drug resistance (some of the most worrying bacteria are commonly resistant to frontline antibiotics). Then they cross-referenced these criteria with regional data to identify the ten diseases without effective vaccines most affecting a particular part of the world. These regional lists were finally combined to form a global list of 17 pathogens that deserve the most focus toward developing vaccines. The researchers’ work, detailing the creation of the list, was published Monday in the journal eBioMedicine.

“Too often global decisions on new vaccines have been solely driven by return on investment, rather than by the number of lives that could be saved in the most vulnerable communities,” said Kate O’Brien, Director of the Immunization, Vaccines and Biologicals Department at WHO, in a statement from the agency. “This study uses broad regional expertise and data to assess vaccines that would not only significantly reduce diseases that greatly impact communities today but also reduce the medical costs that families and health systems face.”

Five germs in particular were identified as priorities for vaccination across all WHO regions: Mycobacterium tuberculosis (the cause of tuberculosis), HIV-1 (the primary cause of HIV in most of the world), Klebsiella pneumoniae, S. aureus, and extra-intestinal pathogenic Escherichia coli. The remaining pathogens were Group A streptococcus, hepatitis C virus, cytomegalovirus, Leishmania parasites, non-typhoidal Salmonella bacteria, norovirus, Plasmodium falciparum (malaria), diarrhea-causing Shigella bacteria, dengue virus, Group B streptococcus, influenza, and respiratory syncytial virus (RSV). The three deadliest diseases on the list, HIV, tuberculosis, and malaria, are estimated to kill 2.5 million people worldwide annually.

Some of these germs already have current vaccines, such as TB and influenza, but these are only partially protective and/or need to be constantly updated in the case of seasonal flu. Some germs have new or improved vaccines that are on the cusp of being approved or widely introduced, such as dengue or RSV. Other germs have vaccines that show promise in early research but are still a while away from being clear winners, such as Shigella or norovirus, while others need much more research to develop viable candidates, such as hepatitis C, HIV-1, and K. pneumoniae.

The WHO’s list is a small part of its larger goal to substantially improve people’s access to vaccination in general by 2030—an effort known as the Immunization Agenda 2030 (IA2030). And the researchers hope their findings can guide and refine the research and development of vaccine programs, both on a local and global level.

“As a community, we can and must tackle these challenges together, and quickly, to fully realize the benefits and enable sustainable impact of existing and future vaccines,” they wrote in the paper. “By heeding these calls to action, we can steer towards the IA2030 vision of ‘A world where everyone, everywhere, at every age, fully benefits from immunization to improve health and well-being.'”