Why the same measures may not have the same effect on different countries
- there would be some difference too between regions of a country, e.g. London vs NW
e.g. some countries have more "innate SD",
from low population density both within a country & within the average household
Adam Kucharski @AdamJKucharski
... another feature of Sweden that stands out is household size
- it's smallest average in Europe, with majority single occupant
(ec.europa.eu/eurostat/web/p…).
What effect could this have on transmission? 1/
The estimated risk of transmission per contact is higher within household than outside household
(thelancet.com/journals/lanin…).
This means it can be helpful to think of an epidemic as a series of within-household outbreaks,
linked by between household transmission... 2/
If the average size of an outbreak in a household is H,
and each infected person within a household spreads infection to C other households in community on average,
then we can think of the
'household' reproduction number as equivalent to H x C 3/
So if household size is smaller in a particular location,
we'd expect H to be smaller,
and hence lead to a lower reproduction number,
even if C is the same... 4/
Now, of course, there are many, many other factors that influence transmission
(behaviour, control measures, immunity, perhaps other seasonal effects).
And it's important to compare countries & understand what might be happening
– and what control measures could be adapted... 5/
But before claiming 'what country X is doing would have same effect here',
we need to consider whether there are key differences in population stucture between countries that might change effectiveness if same measures used elsewhere. 6/6