What policy makers need to know about COVID-19 protective immunity

“Few would disagree that science should guide the clinical therapeutic approach to an infected person. Science must also guide policy decisions.”

This is the central message of a new commentary from researchers at Imperial’s Faculty of Medicine and the National Institute of Allergy and Infectious Diseases (NIAID) published in The Lancet.

The paper highlights how research should inform the response from policy makers to the coronavirus pandemic, particularly with respect to balancing socioeconomic costs against further spread of the disease. The authors also emphasise the importance of using “the best possible data” to underpin policy, given the growing level of interest in understanding the decision-making process behind new public health measures.  

Back to work?

With governments around the world looking to rapidly mitigate the economic impact of the pandemic, the commentary outlines the risks in staggering when individuals return to work based on their risk of being severely impacted by the virus: “[These strategies] do not take account of how exposing even lower-risk individuals…to the virus so as to increase herd immunity can still result in pandemic spread…The only selective pressure on SARS-CoV-2 is transmission—stop transmission and you stop the virus.”

The paper also highlights the need to resolve outstanding issues with the accuracy and practicality of at-home antibody tests before they are used to inform decisions about who can return to work. In addition, the authors underline the risk in assuming that the antibodies measured by these tests equate to effective protection against the virus: “Caution is needed because total measurable antibody is not precisely the same as protective, virus neutralising antibody. Furthermore, studies in COVID-19 show that 10–20% of symptomatically infected people have little or no detectable antibody.”

Defining protective immunity

The commentary emphasises that our understanding of what constitutes effective protective immunity against the virus is patchy and more data are needed to build a clearer picture. Although it may be possible to conclude from current data that individuals who have recovered from severe COVID-19 may have protective antibodies, the authors note that “similar data are urgently needed for individuals with SARS-CoV-2 infection who have not been hospitalised.”

Based on coronaviruses that are closely related to SARS-CoV-2, the authors estimate that immunity to COVID-19 may last for at least twelve months. The paper also suggests monitoring the frequency of reinfection could help to clear up some of the uncertainty surrounding protective immunity to the virus. 

Achieving herd immunity

The commentary explores key questions surrounding herd immunity, a term that refers to when a large proportion of a population has immunity to an infectious disease, thereby providing a degree of protection for those who are not immune.

Using the current estimated R number – or ‘effective reproduction number’ – which signifies the average number of people to which one infected person will transmit the virus, the authors state “the herd immunity calculation suggests that at least 60% of the population would need to have protective immunity, either from natural infection or vaccination.” Crucially, the researchers add that, based on the current data, “it seems likely that natural exposure during this pandemic might, in the short to medium term, not deliver the required level of herd immunity and there will be a substantial need for mass vaccination programmes.”

The commentary emphasises that “safety evaluation of candidate COVID-19 vaccines will need to be of the highest rigour” and that the “delivery of efficacious vaccines is not a competitive race to the finish, but a considered evaluation of a safe, potent, global response.”

‘What policy makers need to know about COVID-19 protective immunity’ by Daniel M Altmann, Daniel C Douek and Rosemary J Boyton is published in The Lancet.

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