26/08/2020
Here's some plan simple facts about herd immunity and Covid 19 .
One of the more sincere questions I get asked by people grappling with the CoVID-19 pandemic is: “if the mortality rate is so low, why don’t we just aim for herd immunity. Surely that would be better than locking us all down?”
Herd immunity is the concept that if enough people are immune to a particular disease, either through naturally acquired immunity or vaccination, that the spread of the disease in the community is arrested, hence protecting vulnerable individuals like the elderly, babies, pregnant women and those with chronic health conditions.
The percentage of people that need to be immune to a disease in order to establish herd immunity in the community varies depending on the disease reproductive number. For CoVID-19 the percentage estimated to achieve herd immunity would be 60% of the population.
The current case mortality rate of CoVID in Australia is around 1.7%. Worldwide case mortality is double this at 3.6%. But for the sake of simplicity let’s use the Australian case mortality rate.
If 60% of the community needs to catch COVID-19 to achieve herd immunity, that means that 14.4 million Australians need to be infected. No problem.
But.....
1.7% will die of the disease. That’s 244,800 dead Australians.
But hey, 98.3% will survive, right?
But international figures show 14% of patients require hospitalisation due to extreme symptoms and complications. That’s 1.96 million Australians that will need admission to hospital.
We only have 62,000 beds available Australia-wide. So what happens to the 1.9 million Australians who need beds but can’t get the medical care to pull through?
But forget them...what’s important is that the really sick Australians get a bed, right?
International figures show that 2% of infected patients require intensive care support. That would mean that 280,000 Australians will require ICU admission.
We have 2378 ICU beds. What happens to the 276,000 critically unwell patients that cannot get an ICU bed?
Aiming for herd immunity in Australia would hence result in:
14.4 million infected Australians.
1.9 million severely infected Australians unable to get a hospital bed.
276,000 critically infected Australians unable to get an ICU bed.
Oh, and the 244,800 Australians that are going to die because ‘it’s only a 1.7% mortality rate’.
But, hey, at least we’ll establish herd immunity, right?
Except for that fact that all evidence points to waning immunity following infection, with antibodies waning after 3 months.
Herd immunity is not an option. Stay home, and stay sensible.
EDIT:
From Elaine Stevenson, Australian Infectious Disease Epidemiologist, who contacted me and is aghast by the Swedish approach:
“Herd immunity is a concept which only applies to vaccine preventable diseases as a measure of program efficacy.
It does not apply to the situation that we are currently in vis a vis COVID-19
We do not have enough follow up on the virus to be anything other than extremely cautious”.
- Sara
