Impending measles outbreak in London?

Impending measles outbreak in London?

by | Sujit Rathod -
Number of replies: 4

A rare post about an infectious disease model, in The Guardian.

"In a population with no immunity, a single case of measles will infect between 10 and 20 others.

To maintain herd immunity, the World Health Organization set a target of 95% vaccination uptake."


Explain how these two statements are mathematically related.

In reply to | Sujit Rathod

Re: Impending measles outbreak in London?

by | MARIA LORA CABRERA TUPAS -

The first statement refers to the R0 or the basic reproduction number, which is the number of secondary infectious individuals resulting from the introduction of a single infectious person into a completely susceptible population. 

The second statement refers to the herd immunity threshold (0.95 or 95%), which is the minimum proportion of the population that need to become immune to measles (through natural immunity or vaccination) in order to decrease measles transmission in the community. The formula for HIT is:

HIT = [1 -  (1/R0)] * [vaccine efficacy]

thus showing how it is related to the basic reproduction number.


In reply to | MARIA LORA CABRERA TUPAS

Re: Impending measles outbreak in London?

by | Sujit Rathod -
Welcome Maria, and well done!

I'll be curious to see how Londoners are encouraged get this vaccine in the coming weeks.
In reply to | Sujit Rathod

Re: Impending measles outbreak in London?

by | RANMINI SUMUDITA KULARATNE -
R0 (average number of secondary cases arising from an index case in a totally susceptible population) = 10-20 (will take average as 15).

Herd Immunity Threshold (HIT): the proportion of population that must be immune to infection in order for disease to remain stable in population (ie R = 1) - each index case produces only one secondary case.

HIT = 1 - (1/R0)

HIT = Vaccine Efficacy * Vaccine Coverage. Can calculate VE if HIT and VC known.

1 - (1/R0) = Vaccine Efficacy * Vaccine Coverage

1- (1/15) = VE * 0.95

VE = 98% (it is known that the efficacy of one dose of measles vaccine approx 95%; efficacy of two doses approx 99%),
In reply to | RANMINI SUMUDITA KULARATNE

Re: Impending measles outbreak in London?

by | Sujit Rathod -
Well done Ranmini!

It's kind of cool how with a couple bits of information like R0 or VE, it's possible to create a policy target.
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