A new study in the Lancet reports on a large scale randomized sero-prevalance study in Spain. Spain had been hit hard by COVID-19 with a quarter million diagnosed cases and approximately 28,000 deaths. We think that for herd immunity to be established, a population needs between two thirds and five sixths to have been infected and recovered with persistent immune capacity built up.
The study did not find that:
Seroprevalence was 5·0% (95% CI 4·7–5·4) by the point-of-care test and 4·6% (4·3–5·0) by immunoassay, with a specificity–sensitivity range of 3·7% (3·3–4·0; both tests positive) to 6·2% (5·8–6·6; either test positive), with no differences by sex and lower seroprevalence in children younger than 10 years (<3·1% by the point-of-care test). There was substantial geographical variability, with higher prevalence around Madrid (>10%) and lower in coastal areas (<3%)….
The majority of the Spanish population is seronegative to SARS-CoV-2 infection, even in hotspot areas… These results emphasise the need for maintaining public health measures to avoid a new epidemic wave.
This increases the confidence in the results out of New York City and other regions that had overwhelmed hospital systems and unconstrained spread: herd immunity in the worst hit areas is not even in vague reach. Lightly hit regions are still at least an order of magnitude of recovered individuals away from talking about herd immunity.
The only ways out are either vaccines, pervasive aggressive and effective public health measures or immense suffering.