This document discusses why early lockdown measures are more effective for slowing the spread of COVID-19. It argues that lockdowns work best when implemented earlier, before case numbers have grown very large. With fewer initial cases, a 20% reduction may leave only a handful of people still spreading the virus, rather than hundreds. It also notes that exponential growth means the virus spreads much faster when case numbers are higher. Therefore, early action through lockdown is vital to curb exponential growth before infections rise dramatically. The key message is that earlier lockdown saves thousands of cases and deaths by slowing the virus when relatively few people are initially infected.

1. WHY EARLY LOCKDOWN
MATTERED
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#covid19 #coronavirus

2. WE’VE HEARD
ABOUT
‘FLATTENING
THE CURVE’

3. AND WE’VE
HEARD HOW
DIFFERENT
MEASURES MAY
HELP… • Hand-washing
• Staying at home if we feel
unwell
• Social distancing
• Lockdown
• Etc.

4. MANY
EXPLANATIONS
SUGGEST THAT
CASE NUMBERS
FLATTEN
EVENLY,
WHENEVER THE
MEASURE IS
INTRODUCED…

5. BUT THAT ISN’T
SO.
IT MATTERS
WHEN MEASURES
ARE
INTRODUCED.
IT REALLY
MATTERS.
Here? Or here? Or here?

6. HERE’S WHY...

7. FIRSTLY, IT IS TO
DO WITH HOW
MANY CASES
THERE ARE AT
THE TIME…
(LOOK AT THE
CROSSES)
A few Many more

8. WHEN THERE ARE
FEW CASES,
LOCKDOWN CAN
BE VERY
EFFECTIVE.
• If, say, lockdown causes a 20%
reduction in cases…
• And there are just 10 cases…
• Then there are only 8 people left to
spread the infection

9. WHEN THERE ARE
LOTS OF CASES,
LOCKDOWN HAS
TO BE MUCH
MORE COMPLETE
TO HAVE THE
SAME EFFECT.
• But a 20% reduction in cases when
there are 1000 cases…
• Means there are still 800 people left
spreading the infection.
• To have only 8 people left out of 1000
would be almost impossible: you’d
need the lockdown to achieve a 99.2%
reduction.

10. SECONDLY, IT IS
TO DO WITH
HOW FAST THE
INFECTION IS
SPREADING…
(YOU CAN TELL
BY HOW STEEP
THE CURVE IS)
Slowly Faster

11. EXPONENTIAL
GROWTH MEANS
CASES INCREASE
VERY, VERY FAST.
• When every person passes the infection to 3
others within 5 days...
• 8 people will infect 24 others
• Then 24 people will infect 72 others
• 72 people will infect 216 others
• 216 people will infect 648
• 648 people will infect 1944
• And so on. You get from 8 infected people to
thousands in just a few weeks.

12. EARLY ACTION IS
VITAL TO STOP
EXPONENTIAL-
READ OF
INFECTION . • When every person passes the infection
to 3 others within 5 days...
• If only 8 people are infected, you will
have 1944 infected after 25 days.
• If 800 people are infected, you may
have 194,400 infected after 25 days.

13. THIS ANIMATION
ALSO SHOWS WHY
EARLY ACTION IS
MORE EFFECTIVE
THAN LATER ACTION

14. SO…
• Covid-19 was spreading exponentially before lockdown
• Lockdown slowed the growth
• Earlier lockdown when there were fewer cases would have
meant thousands fewer cases and deaths.
thisfionaweir 2020