Covid-19 cases have now topped 13 million cases worldwide with several countries, including the US, still seeing a steep rise in the number of new cases each day. With the rapid spread of the virus, the question of when and if will herd immunity provide a protective effect, continues to be asked. New data suggests that some hard-hit communities may be better protected for Covid resurgence, while other communities are not.
Figure 1 presents the estimated percentage of seroprevalence in a community in Queens NY, Spain, and Geneva, Switzerland.
Figure 1: Covid-19 Serological Prevalence Estimates
Source: GlobalData; Goldstein, 2020; Stringhini et al., 2020; Pollan et al., 2020
*Extrapolated to Queens, NY based on data from one clinic in Queens, NY
Knowing the number of new cases, recoveries, and deaths are vital to understanding the ongoing spread of this current pandemic. However, these data do not provide a total percentage of the population that has been infected. In order to capture this metric, serological prevalence studies need to be conducted to test for the presence of antibodies towards the novel virus. The results of these types of studies can then help estimate the level to which a community or an entire country has been infected by the disease and provide predictive insights as to what may happen if the virus resurges.
Given that two of the hardest-hit countries in Europe only show between 5–10% serological prevalence for Covid-19 despite the high infectivity provides a grim outlook for many of the countries that have been unable to curb the spread of the virus in this first wave. Although, results of testing data from Queens, NY suggests that some smaller communities, that have been very hard hit, may indeed be at the level of the population infected, thought to be around 70%, needed to offer some protection through herd immunity. Some more general estimates, however, suggest that New York City, on the whole, is nowhere near the 70% mark and could be as low as 20% population prevalence despite being an epicentre for this disease.
As the pandemic continues to spread, data will continue to be collected and shed light on the current situation. Additionally, herd immunity will only work if an immunity to the virus can be maintained sufficiently long and if the virus does not mutate in a way that prevents the previous infection from providing a protective effect. Both of these key details still remain unclear. Based on these data, the failure in the US to adopt the widespread use of preventive measures and the early reopening of the economy is likely to only increase the number of cases of Covid-19 but whether or not this will provide enough immunity in the country to prevent resurgence seems unlikely.
As this is a continuously developing situation globally, more research and data is needed to truly understand the impact of Covid-19.