12 week dosing interval for the two COVID-19 vaccines in the UK – an analogy

Saad Shakir on Pharmacovigilance:

Obviously hepatitis A is a different virus with a different vaccine platform. However, analogies are very useful in science.

This is an abstract from the Summary of Product Characteristics (SmPC) of Avaxim – an inactivated hepatitis A vaccine:

“The first dose is for initial protection and the second dose, which can be given somewhat flexible time after that is for long term protection
Initial protection is achieved with one single dose of vaccine. Protective levels of antibody may not be reached until 14 days after administration of the vaccine.

In order to provide long-term protection, a second dose (booster) of an inactivated hepatitis A vaccine should be given. The second dose is preferably given between 6 and 12 months but may be administered up to 36 months after the first dose. It is predicted that HAV antibodies persist for many years (beyond 10 years) after the second dose.”

The exploratory analyses and assumptions about the 12 week dosing interval for COVID-19 vaccines (which I agree with) need to be quickly supplemented by antibody measurements and epidemiological observations during weeks 5 to 12 after the first dose.