COVID Odyssey: Worldwide Winter Windup 10 ~ Vaccine hesitancy ~ is herd immunity possible?

The vaccine hesitant includes a range of people ranging from people fearful of getting a jab, those fearful of the consequences of getting a jab, to anti-vaxxers.

‘Herd immunity’, also known as ‘population immunity’, is the indirect protection from an infectious disease that happens when a population is immune either through vaccination or immunity developed through previous infection. WHO supports achieving ‘herd immunity’ through vaccination, not by allowing a disease to spread through any segment of the population, as this would result in unnecessary cases and deaths.


For more definitions see:


A large theoretical literature shows how to derive R0 for
different infections, often implying that the 1 – 1/R0
threshold be used as a target for immunization coverage
and that its achievement can lead to eradication of target


Recent research into New Zealanders’ attitudes to vaccination suggest positions have become more polarised over the last decade, with 60% identifying as “vaccine believers” and 30% as “vaccine sceptics”.

In New Zealand

The overall potential uptake, including those already vaccinated and those who are likely to get a vaccine is estimated to be 79%, from 77% in June, 80% in May and 77% in April. The difference from June is not statistically significant and the result should be regarded as “no change”.

Similarly in the USA A study of more than 1,000 demographically representative participants found that about 22% of Americans self-identify as anti-vaxxers, and tend to embrace the label as a form of social identity.

According to the study by researchers including Texas A&M University School of Public Health assistant professor Timothy Callaghan, 8% of this group “always” self-identify this way, with 14% “sometimes” identifying as part of the anti-vaccine movement.

. . .

“The fact that 22% of Americans at least sometimes identify as anti-vaxxers was much higher than expected and demonstrates the scope of the challenge in vaccinating the population against COVID-19 and other vaccine-preventable diseases,” he says.


‘Concerning’ number of Americans identify as anti-vaxxers

Below is a graph showing the percentage of the population that needs to get vaccinated to achieve herd immunity:


This version may be easier to read:


Ro (R0) is the number of people that one person may infect on average in a population where no one is immune.

For the Delta variant of COVID-19 Ro has been estimated between 5 and 8 people.

We have used the same range to estimate Ro for the initial outbreak of COVID-19 in early 2020.

For the Delta variant we have estimated Ro to be between 9 and 12.75.

Regardless, when Ro = 5, from the graph, 80% of a population would need to be vaccinated to achieve herd immunity.

When Ro = 8, the percentage rises to 87.5%.

When Ro =9, we need almost 89% to be immunised.

When Ro =10, we have about 90% and when Ro = 12.75, over 92%.

The graph is created from this table:


Clearly herd immunity is unlikely even when Ro = 8 unless many of the vaccine hesitant get immunised or get a level of immunity when they get infected with COVID-19.

We do not wish anyone to get COVID-19.

At least half of the vaccine hesitant may need to get vaccinated before we get anywhere near a 90% vaccination level in New Zealand.

Do you think a 90% vaccination rate is achievable in NZ?

If you do think 90% is achievable, how soon do you think this may be achieved?

Also see the NZ Herald on Sunday 19 September p6:


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