Herd immunity and the coronavirus

Stephen Leeder

The first preliminary (Phase 1) trial in humans of a coronavirus vaccine in the US is a good moment for reflection on the immunology of this illness.

We need to be cautious. It is not the virus that leads to interstitial lung disease and death. It is our immunological response, the “cytokine storm”, that causes severe illness.

This is comparable to the devastation of the respiratory syncytial virus, persistently responsible for bronchiolitis in the very young, killing tens of thousands worldwide each year.

If the vaccine is both effective and safe, enough people will be immune, and transmission from them to the rest of us will be much diminished. Indeed, if enough people are immune — generally about 60% (“herd immunity”) — either through exposure or vaccination, transmission ceases.

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IEA Statement on the Novel Coronavirus (COVID-19) Pandemic

The Council of the International Epidemiological Association, its affiliate bodies and members have viewed with concern the rapidly evolving situation with the novel Coronavirus (COVID-19) pandemic. Since the onset of the outbreak in December 2019, this disease has affected 162 countries and territories (as of 17/03/2020) with over 184,000 people affected and 7,000 deaths. With countries at various response stages of anticipation, early detection, containment, and mitigation, we commend the efforts of the WHO, various national governments, non-governmental organizations, health workers and advocates in addressing this health crisis.

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