22 March 2021 Blog: COVID-19 Metrics at Historic Lows in Los Angeles County

There is increasing discussion across the US about the potential for a 4th wave of COVID-19 infections – but there is no indication of such occurring at this time in Los Angeles County.  

Such an instance would occur due to the intersection of increasingly contagious variants and inadequate population immunity.  Because population immunity is a function of natural infection and vaccination, any such 4th surge in COVID-19 cases would be the direct result of a failed vaccine rollout.  Why?  Because, without exception, all known variants have been shown to be susceptible to the neutralizing antibodies provided by the three vaccines on the market – Pfizer, Moderna and Johnson & Johnson.

Earlier this week, published in Lancet, a Danish study estimated that the net effectiveness of natural COVID-19 infection against a subsequent re-infection was about 80% at six months.  However, among those over the age of 65 years, this rate of protection dropped to 47%. While Los Angeles experienced its greatest surge in early January (Figure 1), during which at least 25% of the population became infected, our chief defense against a 4th surge is a swift, effective and encompassing vaccination effort.

As a County, we are currently in our 10th straight week of decline.  Prevalence (the estimated proportion of individuals with active infection) in Los Angeles is now less than 1 in 1,000 (actually 0.98 per 1000 population for those keeping score at home) which is the lowest rate it has been in 52 weeks (Figure 1).

New (incident) cases are at a level also not seen since March 2020 – 4.7 new daily cases per 100,000 population (Figure 2). 

Mortality is down to 0.2 daily deaths per 100,000 (Figure 3), a rate last seen in April 2020.

Yes testing rates are falling but so are positivity rates which are beneath 2% – a historic low. The most recent estimate for Rt (effective reproduction number) for Los Angeles County stands at 0.59 (source: http://metrics.covid19-analysis.org) indicating that each new COVID-19 case will lead to less than one additional case – meaning that on its current trajectory, COVID -19 will eventually disappear.

So, at this writing, there is no evidence that we are heading for a 4th wave here in Los Angeles.  Continued improvement in case numbers, however, will be dependent on a County government led vaccine rollout which, once again, will only focus on delivering second shots this week..

𝗦𝗶𝗴𝗻 𝗨𝗽 𝗳𝗼𝗿 𝗢𝘂𝗿 𝗡𝗲𝘄𝘀𝗹𝗲𝘁𝘁𝗲𝗿

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