Mass vaccinations can't prevent Ebola outbreaks

The World Health Organisation (WHO) has announced a new Ebola virus outbreak in the Democratic Republic of Kongo. However, a recent research suggests prophylactic mass vaccination programmes are not a realistic option in the battle to prevent the disease.

Ebola virus outbreak control depends on surveillance and the isolation of cases, according to the study.

It revealed that very high proportions of potentially affected populations would need to be protected by vaccination to establish herd immunity, i.e. the level of immunity that prevents virus transmission within a population.

At this level, 80 percent of a population would need to be immunised to prevent outbreaks, even if a highly effective vaccine that protects 90 percent of individuals after vaccination was available.

Such vaccination rates are currently unachievable. In a vaccination trial during the West African Ebola virus epidemic, only 49 percent of individuals who had been in contact with Ebola virus patients could be vaccinated. 34 percent of contacts refused vaccination although they had been exposed to the disease.

There are currently no clinical vaccine candidates available that protect against all four human-pathogenic Ebola viruses.

A large vaccination programme would also be costly and impractical, the study points out. Some 462 million people are living in the areas affected by Ebola virus outbreaks, many of them in very remote rural areas.

The study pointed out that the clinical vaccine candidates will need to be focused on health care workers who are often involved in disease transmission, potentially in combination with the vaccination of patient contacts.

The study appeared in the journal Frontiers in Immunology.