Herd immunization or community quarantine?
READER’S VIEWS (The Freeman) - April 24, 2020 - 12:00am

When COVID-19 hits a country the society is unprepared, one infected spreads the virus to three others. The number of infected grows exponentially to 9, 27, 81, 243 etc. Experience shows: The COVID-19 Basic Reproduction Number R(0) is 3. For mumps and influenza it is 2, for the highly contagious measles it is 15.

Since no vaccine is available yet the only way to break the rapid spread is non-pharmaceutical intervention i.e. isolation, community quarantine.

First target is to reduce the R(0) to 1. If 1 infected infects only one person, the number of sick remains constant. But the initially infected two persons hopefully cure and are now immune. In every infection cycle the number of immune people gets bigger in comparison to the unhampered spread under R(0) = 3 and also in comparison to the infected persons under R(0) = 1.

Scientists say: When the number of immune people reaches 60 to 70 % of a given society, the remaining 30 to 40 % still infected and sick are unlikely to meet unimmunized people. They hopefully also cure and the society is healthy again.

The “herd” has lost some members but it has survived the epidemic and is immune now against COVID -19.

If in an even more disciplined society the R(0) is smaller than 1, the 60 to 70 % target is reached earlier. The last coughing and sneezing throws the virus to the ground where it dries in the sunlight and perishes as happened in China.

The formula for Herd Immunity is H = 1 minus (1 divided by R(0)) in case of COVID-19: H = 1 minus (1 divided by 3)  or H = 1 minus 1 third which is H = 2 thirds or 66% right within the 60 to 70 % target.

Herd Immunization is used in Israeli kibbutzim kindergartens as soon as measles break out. Within 2 days all kids are infected and within a week or so all are through and naturally immune for life without vaccine. Since the measles virus is far less virulent than COVID-19, no kid dies.

In the United Kingdom Prime Minister Boris Johnson initially proposed herd immunization on the British Island. That would have meant to let 40 million people get infected and sick with a chance to recover or die. But the Queen’s subjects protested and Johnson dropped his plan within the day.

So, what do we prefer in the Philippines in the absence of a vaccine and medicines? Herd immunization or community quarantine?

Erich Wannemacher

Lapu-Lapu City

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