New US study shows profound impact of COVID-19 vaccination

Jolyon Attwooll

31/08/2021 3:28:02 PM

Analysis of more than 40,000 cases suggests unvaccinated people are almost 30 times more likely to be hospitalised.

Doctors attending to ICU patient
Results of the studies add to existing real-world evidence of the efficacy of the vaccination program.


A wide-ranging analysis in California has given detailed, real-world results highlighting the protection offered by COVID-19 vaccines.
The study, which was carried out in Los Angeles County, found unvaccinated people are almost 30 times more likely to be hospitalised by COVID-19 once the results are adjusted for age.
The Los Angeles County Department of Public Health carried out the research, which has now been published on the US Centers for Disease Control and Prevention (CDC) website.
Researchers tracked infections from 1 May to 25 July this year, a period that coincided with the Delta variant becoming the dominant strain in the US.
Of 43,127 COVID-19 cases, 10,895 (25.3%) were identified in fully vaccinated residents, 1431 (3.3%) were recorded among the partially vaccinated, while 30,801 cases (71.4%) were found among unvaccinated people.
Calculations, made to show the level of cases per 100,000 residents among the different groups, were designed to account for the rapidly increasing vaccination rates during the time of the study.
Once adjusted for age, results indicated that rates of hospitalisation were 29.2 times higher among the unvaccinated compared to the vaccinated as of 25 July.
The differences were substantial but less dramatic for infectious cases, with the rate of COVID-19 infections among unvaccinated people tracked at 4.9 times the proportion of those who had completed a full vaccination program.
Professor Robert Booy, a vaccine expert at the University of Sydney, said the results add to existing real-world evidence of the efficacy of the vaccination program.
‘Vaccination works. It’s safe, it’s effective – but it’s not perfect,’ he told newsGP. ‘What vaccination does is provide 90–95% protection against serious disease, hospitalisation and death, which all doctors know.
‘What [vaccination] can’t do is prevent a high proportion of infection.
‘When you get a “breakthrough infection” – that is to say evidence of COVID even though you have been vaccinated – it almost always is mild.
‘You see an increasing effect on more severe illness, and that’s what you would want. You wouldn’t want something to prevent mild illness and not prevent the severe end.
‘What you are getting is the maximum bang for your buck at the severe end of the spectrum of the disease.’
In the Los Angeles public health research, Pfizer was the most used vaccine among the study cohort (55 %), followed by Moderna (28%), and the one-dose Johnson & Johnson vaccine (16%).
As from the earliest stages of the pandemic, age was a crucial factor. There were more hospital and intensive care admissions among older vaccinated people, where the median age was reported as 64. The median age for hospitalisations among unvaccinated people was substantially lower at 49.
Recent outbreaks in Australia have shown a similar trend, with more people from younger age groups admitted to hospital. The NSW Department of Health reports that around a quarter of those currently in hospital are aged under 40.
The most recent COVID-19 weekly surveillance report from NSW showed 21 deaths linked to COVID-19, including five who were fully vaccinated. All of those who died after being fully vaccinated were in their 70s and older.
The Los Angeles study reported 24 deaths among fully vaccinated people, compared to 176 among the unvaccinated. At least six of the 24 deaths were among those who already had underlying health conditions.
While the results from the Californian study show the early efficacy of the vaccines, they do not allow any conclusions to be drawn on how long the protection will last.
‘We’ve never done better surveillance, so we will never know sooner the ongoing real-time impact of vaccination,’ Professor Booy said.
‘By Christmas, we should have important data and know whether we need boosters for at-risk people [next year].’
The lineage of the SARS-CoV-2 variant was also tracked through whole-genome sequencing. The Los Angeles study, which included those aged 16 and older, indicated the cycle threshold (CT) values were broadly comparable in vaccinated, unvaccinated, and partially vaccinated people.
This was a trend which shifted as the Delta strain became the most common variant, with more variation in CT values found among those tested earlier in the study.
On the other side of the US, New York City health authorities have also recently published the results of an analysis of infections, hospitalisations and deaths since the first residents became fully vaccinated in the area.
These echoed the findings of the Los Angeles County research, showing marked differences between the health outcomes of those who contracted COVID-19 after vaccination, and those who got ill without vaccine protection.
The study concluded that 96.1% of all COVID-19 cases, 96.9% of COVID-19 hospitalisations and 97.3% of COVID-19 deaths between 17 January and 17 August were among people who did not have any vaccination protection.
The age-adjusted hospitalisation rate in that study was less dramatic than that found in the Los Angeles research, but still striking. It stood at 23.5 per 100,000 unvaccinated residents compared to 2.4 among those who had gone through the full vaccination process.
This article was updated on 2 September at 10:30 am to include the most recent details on the vaccination status of people who have died from COVID-19.

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Dr W Fischer   1/09/2021 7:14:22 AM

Thankfully those vaccines are so effective that they now need booster shots as a matter of urgency for everybody