A research comprising of 15 years, conducted in Kilifi, Kenya and funded by the Wellcome Trust and Gavi, the Vaccine Alliance has dismissed the need to give booster doses of influenza type b (Hib) vaccines to toddlers. The study supposedly provides sufficient evidence for health professionals to be certain that the spread and incidence of Hib in Kenya is under control.

No Need For Hib Booster For Vaccinated Infants In Kenya

Hib bacteria cause meningitis, pneumonia and other possibly fatal infections, especially in children under the age of five. In 2001, Kenya introduced a vaccination program designed to provide immunity against the bacteria during infancy, and to prevent its spread among young children. The babies are vaccinated at the ages of six, 10 and 14 weeks.

In high-income countries, such as the UK and Australia, it is a fairly common practice to administer an additional booster dose after immunity via the previous doses begins to fade away. However, Kenya, along with many other low-income countries, had adopted the World Health Organization (WHO) vaccination regime without a booster dose.

“We’d expected that with time population immunity would decline, but even after 15 years this still hasn’t happened”, reassured lead researcher Professor Anthony Scott, who is based at the KEMRI-Wellcome Research Programme in Kilifi, Kenya and the London School of Hygiene & Tropical Medicine, UK. He added that despite concerns that arose from episodes in other countries, no fourth dose of the Hib vaccine was required to control the bacterium in Kenya.

After analyzing blood samples of more than 38,000 children under the ages of 13 for 15 years to monitor the trend of invasive Hib disease, researchers concluded that the current vaccination regime reduced the risk of disease by 93 percent. They also evaluated healthy vaccinated children and saw that after eight years of being vaccinated, 79 percent of children in the risk group (between four and 35 months) had a sufficient titer of antibodies for long-term protection. Moreover, an assessment of nose swabs from the general public found Hib in only one child out of 600.

What Makes Vaccination In Kenya Stand Out?

First author Dr Laura Hammitt, from Johns Hopkins Bloomberg School of Public Health stated that the findings of the study suggest that the vaccination program in Kenya is extremely efficient and hence requires no booster doses. However, continued surveillance is required to determine whether this remains true.

Researches have stated various reasons for the results obtained. They believe that bacteria similar to Hib are present in the environment and provide a natural boost to the immune system and antibody titers. Secondly, a more vigorous antibody response to the vaccine has conferred long-term protection to infants in Kenya as opposed to developed countries such as the UK. The same findings could also be seen in other tropical regions of Africa.

Providing Booster Doses: Different Countries Adopt Different Stances

Conjugate Haemophilus influenzae type b (Hib) vaccination is among the major global health achievements in the last 40 years. At the time of its introduction, the main impact of the disease was seen in low-income countries, particularly targeting infants and young children.

The study conducted in Kenya assesses the effectiveness of the Hib vaccine, its nasopharyngeal carriage and population immunity. After receiving a three-dose primary vaccination of conjugate Hib, a significant reduction in invasive Hib disease was seen in the Kilifi district of Kenya over a period of 13 years. A similar sustained long-term control of disease following the same schedule was also seen in The Gambia, Africa.

Currently, more than 90 percent of countries routinely vaccinate their children; however, the statistics revealed in Kenya have started a worldwide debate about the dosing schedule: developed countries provide booster doses at the age of 12-23 months, whereas many low-income countries adopt the WHO vaccination regime of three doses without booster. For health agencies and experts, this difference in vaccination regimes is proving to be a real problem.

Reasons For Alarm: Why Booster Doses Must Not Be Ignored

So why shouldn’t we simply abandon the need for booster doses and adopt the three-dose vaccination regime? There are many significant reasons.

  • Although The Gambia saw a success with the three-doses without a booster dose regime, eastern Gambia experienced an unexpected and unexplained resurgence of the disease in 2015 – more than 10 years after following the no booster program.
  • Effective long-term control has not been seen in all countries adopting the three-dose primary schedule. Take the UK for example. They introduced the vaccine in 1993 without scheduling a booster dose. Despite excellent initial control ( influenzaetype b was eliminated from the upper respiratory tract), a resurgence was seen after several years. This made the UK introduce a booster dose in 2003, which resulted in better control and prevention of the disease. A similar experience occurred in Ireland as well.
  • A theoretical reason to worry is the fact that immunity to the bacterium may wane over many years. In this state, the vaccinated group might develop a new reservoir of Hib carriage that could cause mild disease, and develop into a more severe infection later on. Such an instance occurred in Mexico, where waning immunity forced health officials to introduce a booster dose in 2007.
  • The Hib vaccine hasn’t been used long enough in low-income countries to adequately assess the possibility of dwindling immunity and resurgence. Hence, the results of the study conducted in Kenya are not enough to completely dismiss booster doses.

Concluding Recommendations On Influenza Vaccines

There is sufficient evidence suggesting that the general image of booster doses being unsafe and unnecessary is rather unreasonable. Developed as well as developing countries must understand that by denying the public these additional vaccinations they are exposing them to severe resurges that could take years to develop, but could be fatal.

The solution seems to be enforcing a unified global policy of booster doses, but budget constraints, competing priorities, complicated logistics, and, most importantly, a lack of sufficient evidence are all key factors that need to be accounted for. Hence, the following steps may be taken:

  • Countries need to firstly establish vigilant disease surveillance to effectively measure the incidence and prevalence of influenzae type b infections.
  • Importance of control and the threat of resurgence must be better comprehended to avoid any unprepared outbreaks.

Via long-term evaluation, researchers conclude that children in different countries have slightly different levels of response to a single vaccine. Using this key finding, they are now taking initiative to develop and enforce the most suitable and personalized vaccination regime for each country.