California and New York may already have got herd immunity, study shows

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In a new study, researchers suggest that New York and California may have reached herd immunity.

The findings are based on the SIR Model of Infection Dynamics, which is being used to determine COVID-19 scenarios.

This model can show how different public health interventions may affect the spread of the epidemic, such as the most efficient technique for issuing a limited number of vaccines in a given population.

The research was conducted by a team at Ben-Gurion University of the Negev (BGU).

In late June, New York State was close to reaching herd immunity, according to the SIR model, which is defined by a disease reproduction number of less than one.

Considering a steady decrease in reported mortality rates since then, the basic reproduction number under the current social distancing restrictions was 1.14.

The basic reproduction number is the average amount of secondary infections an infected person will cause in a completely susceptible population.

At that time, New York had approximately 400,000 confirmed cases, implying 2.4 million (6x more) actual infections based on the results of serological tests conducted in the state.

The team says that these are similar to the estimates for California and Israel.

In California, it appears that herd immunity was reached around July 15 with slightly more than 10% of their population (4.05 million) being infected.

This means that their basic reproduction number R0 under current restrictions is only 1.1.

In Israel, a further lockdown is not necessary if the current restrictions are maintained and there are no unusual spreading events.

If we maintain the current restrictions, then my model predicts that we are at the end of this peak, which should tail off at the end of August or the beginning of September.

Moreover, according to the calculations, scientists need 1.16 million people with antibodies in order to achieve herd immunity and we are very close to that number.

If there is no unusual outbreak because of the return to school or mass indoor gatherings, then the infection rate will start dropping.

While another lockdown would certainly reduce infection rates, there is no need at the present time since social and physical distancing is working to lower infection rates.

However, the outlook for COVID-19 patients admitted to intensive care units in Israel for COVID-19 is dire, with an estimated 80% mortality rate.

According to the World Health Organization, the global percentage is currently about 60%.

In previous research unconnected to COVID-19, the team revealed that there is an average 20% mortality among all patients admitted to ICUs.

The team says people are heading in the right direction, but it is important not to relax the restrictions or get overconfident.

One author of the study is data scientist Prof. Mark Last.

The study was presented at the Artificial Intelligence and the Coronavirus workshop at the International Conference on Artificial Intelligence in Medicine (AIME).

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