That same 7-day Covid test positivity rate has also increased over roughly the same time frame in the state’s most populous county, Los Angeles. LA hit its last low in early June at just over 0.4%. As of Wednesday, the county’s test positivity rate had risen to 0.8%. (See table below – which does not include the last week of data.)
Covid-19 update in the United States: a more transmissible Delta variant now 20% of new cases; Children most at risk
The test positivity rate is, as the name suggests, a measure of the prevalence of new infections. It is calculated as the number of positive tests divided by the total number of tests performed. Averaging the rate over a week eliminates data problems and, since the statistic is relative to the number of tests, it is not affected by peaks and troughs in the raw number of tests administered.
This is important, given that the number of tests administered in the state has declined and is now lower at any time during the past year. Fewer tests can mean fewer identified cases and provide an incomplete view of a pandemic. Test positivity is a more accurate measure of the increase and decrease in cases.
The increase in test positivity is admittedly small, but it is of concern when viewed alongside data indicating a growing increase in the highly infectious Delta variant of Covid-19 in the state.
In the same week that Gov. Gavin Newsom abandoned statewide Covid restrictions, Delta grew by around 40%. Last week, the state also declared Delta a “variant of concern” for the first time.
The strain had barely registered on the weekly variant tally released by the HQ Department of Public Health. But on Thursday, the number of cases related to Delta and associated variants discovered in the state rose from 286 to 399. That represents an increase of about 40% week-over-week.
The CDC announced earlier this week that the percentage of Covid infections in the United States represented by Delta had doubled every two weeks to 20% on Tuesday.
Los Angeles County Public Health Director Barbara Ferrer noted again on Wednesday that the variant was also spreading locally, particularly among unvaccinated people.
As of last week, 64 cases of Delta have been detected in LA County, and their number has been increasing steadily since late April. Ferrer is expected to release updated figures on Thursday and she expects a “significant increase”.
“Because we, like every other place in the United States and indeed other places in the world where they see the Delta variant, it’s actually proliferating very quickly,” she told the board. . “This is the most infectious variant that has been identified to date here in California, and that means for unvaccinated people it will pose a big risk because it spreads so easily. “
According to figures released on Monday, the county officially surpassed the 10 million doses of the Covid vaccine administered, with 58% of the population aged 16 and over considered fully vaccinated, and 67% of the population aged 16+ at least partially vaccinated. State numbers are roughly comparable, which is important given that Pfizer shots, at least, are said to be 88% effective against the Delta variant. This makes the population as a whole the most vulnerable, children under 12 who are not yet eligible for vaccination.