Why the gap between live vaccines?
AThere are two reasons. First, a simultaneous challenge to the immune system may result in reduced immune response to both vaccines.
Even if it does occur, it may not be a sufficiently large reduction to impair the protective effect significantly.
There is evidence combining Hib vaccine
with certain types of DTP results in a reduction in response to Hib.
MMR is the best example of simultaneous administration of multiple live attenuated viral vaccines. Here, the combination is known not to reduce the protective effect of each component, as the combined vaccine is as effective as spaced injections of individual components.
The second reason is additive side-effects, as live vaccines tend to cause systemic symptoms. Some, such as yellow fever and Japanese B encephalitis, have very high risks of significant side-effects. Yellow fever vaccine has been associated with multi-organ failure in the elderly, while Japanese B encephalitis is associated with severe allergic reactions. It is prudent to administer these separately.
There does not appear to be a problem about simultaneous administration of inactivated viral and bacterial vaccines, such as influenza and pneumococcal polysaccharide, or a live vaccine with an inactivated vaccine.
If viral vaccines are pre-packaged together it will be safe to administer simultaneously. If they are not, one should not assume it would be safe to administer them together without seeking further advice.
Dr Gavin Spickett is a consultant immunologist at the Royal Victoria Infirmary, Newcastle-upon-Tyne