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The 24 – 30 April is World Immunisation Week with the focus of this year’s WHO campaign is “Close the immunisation gap”.  NDM and Paediatrics spoke to Professor Calman MacLennan, Professor of Vaccine Immunology (University of Birmingham) and Jenner Investigator and Dr Manish Sadarangani Clinical Lecturer and Honorary Consultant in Paediatric Infectious Diseases and Immunology at The Children’s Hospital, Oxford about vaccinations and how we can “close the gap” and get more people vaccinated to prevent deadly diseases.  

 

Cal MacLennanTo mark World Immunisation Week, Professor Calman MacLennan, Professor of Vaccine Immunology (University of Birmingham) and Jenner Investigator discusses the importance of vaccination and developing new vaccines.

Q: Why should we vaccinate children?

Calman MacLennan: Vaccination has proven over the years to be the most effective and cost-efficient medical intervention we have available. Vaccines have had a greater impact on disease prevention and lives saved compared to anything other than improved water supplies and sanitation. Time and again, the incidence of specific infectious diseases has fallen dramatically after national introduction of a new vaccine. For example, the Haemophilus influenzae  b vaccine, otherwise known as the Hib vaccine. Children under 5 years of age are often the age group most susceptible to infectious diseases. Therefore, for vaccination strategies to be most effective, it is important to target this age group. This is the reason why so many routine vaccinations are given in the first year of life.

Q: Can you still catch a disease if you have been vaccinated?

CML: Although vaccination will reduce the likelihood of developing the disease, the degree of protection varies from vaccine to vaccine and there is rarely 100% protection. There are several reasons for this. Natural variation among infectious agents, such as bacteria and viruses, means that the immune response triggered by vaccination will not recognise all the various forms of that infectious agent. This natural variation is a problem for current flu vaccines and for groups trying to develop vaccines against malaria and HIV. Also, the immune response following vaccination will wane with time and so an individual can change from being protected against an infection, back to a state of being susceptible. This is the reason why we often use vaccine booster doses.

Q: Are there any differences between naturally-acquired and vaccine-acquired immunity?

CML: Yes, depending on the vaccine and infection. Naturally-acquired immunity will tend to be against the whole of an infectious agent, since that is what is triggering the immune response. Many modern vaccines are known as subunit vaccines, because they only contain one or a few components of an infectious agent. For instance, the surface sugars of certain bacteria may be altered by being linked to other molecules or mixed with agents known as adjuvants that help the body make a more protective immune response. With such subunit vaccines, the chosen components of the bacterium or virus are usually those that are most likely to result in protection. Interestingly, naturally-acquired immunity does not always lead to protection against re-infection, while vaccines are designed to result in a protective response in as many people as possible.

Q: How is your research helping to develop vaccines?

CML: I’ve recently returned to the University of Oxford after 4 ½ years running research at a global health vaccines institute in Italy. During that time, I was involved in research to develop vaccines against different forms of Salmonella infections, including typhoid, paratyphoid and non-typhoidal Salmonella; Shigella dysentery; and meningococcal meningitis. The typhoid and paratyphoid vaccines have now been licenced to a major vaccine manufacturer. Back in Oxford, my research follows two main themes. The first is directed towards understanding the science behind the vaccines I was developing in industry. This involves field work in various African countries, studying immunity in patients with the diseases the vaccines aim to prevent, particularly Salmonella infections, and in population groups that are known to be highly susceptible to these diseases. Such work can help improve the vaccines currently in development and help design better 2nd generation vaccines. The other theme involves the development of new vaccines against key diseases for which there are currently no vaccines available. One such project is to develop a vaccine to protect people against gonorrhoea, a disease which is becoming an increasing problem due to high levels of resistance to antibiotics.

Q: What do you think we can do to ‘close the immunisation gap?’

CML: Although in industrialised countries, such as the UK, there are very well developed systems to ensure that all people receive the routine vaccines they require in childhood and throughout life, this is not the case throughout the world, particularly in low and middle income countries. Many thousands of lives are lost each year in the developing world, particularly among children under five years of age, to infectious diseases for which vaccines are already available. Closing this immunisation gap between the developed and developing world requires a combination of political will and availability of funding, in order to ensure that these licenced vaccines are made accessible to all. However, there are many key diseases that particularly affect the developing world for which no vaccines are available, or current vaccines are sub-optimal, including malaria, HIV, TB and a range of diarrheal diseases. The Jenner Institute is working to develop vaccines against many of these diseases, and in this way, we can contribute to closing the immunisation gap.

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