CDC COVID report ‘no cause for panic’

Jolyon Attwooll

4/08/2021 5:01:00 PM

A new study suggesting vaccinated and unvaccinated people who contract COVID have similar viral loads has been questioned.

Graphic representing transmission.
The CDC says the Massachusetts outbreak reinforces the need for ongoing prevention strategies in public places, like mask wearing.

A report released by the US Centers for Disease Control and Prevention (CDC) on 30 July has pressed for ongoing prevention measures, even as the tally of fully vaccinated people rises.
It included an analysis of an outbreak that occurred in Massachusetts last month, where a large number of infections was linked to public events and large gatherings.
It led to 469 confirmed cases of COVID-19, of which 74% were among people who had been fully vaccinated – a proportion that roughly corresponds to the area’s level of vaccination coverage, cited at 69%.
The report says the fully vaccinated were defined as a having had a two-dose course of Pfizer or Moderna, or a single dose of the Johnson & Johnson vaccine at least 14 days before they were exposed to the virus.
The Delta variant was present in 89% of those who had genomic tests.
But while the authors note that the viral load of vaccinated and unvaccinated individuals infected with SARS-CoV-2 could be similar, vaccine expert Professor Robert Booy from the University of Sydney said caution should be exercised when interpreting the report.
‘It’s an outbreak report with reasonable detail but many caveats,’ he told newsGP.
As well as the circumstances surrounding the outbreak not being representative, Professor Booy says the way viral loads were assessed in the study – by RT-PCR diagnostic tests – was not ideal.
‘It’s not the reliable way to do this. They have taken the opportunity to make a chance observation, which requires a lot more research to be confirmed,’ he said.
‘We know already that when breakthrough infection occurs, and actual viral load is measured that you can have similar viral loads in breakthrough cases as you do with primary cases.
‘However, within days of infection, the viral load in vaccinated people drops much more rapidly and therefore makes them much less likely to transmit and much less likely to be hospitalised or die.
‘At diagnosis there may be a similar load but there are dynamic occurrences after that point which lead to vaccinated people having fewer symptoms and being less likely to transmit.’
The CDC did note that further microbiological research would be needed to establish the relative viral loads in fully vaccinated people.
A separate pre-print study published on Wednesday, this time conducted by Imperial College London (ICL), has estimated that fully vaccinated people have around 50–60% reduced risk of COVID-19 infection compared to unvaccinated people. The protection rises when asymptomatic people are excluded from the figures.
Double vaccinated people are less likely than unvaccinated people of testing positive after being in contact with a COVID-19 case (3.84% vs 7.23%), the authors concluded.
Steven Riley, a Professor of Infectious Disease Dynamics at ICL, said more research is needed to understand how transmissible the virus can be among those who have received the vaccine.
‘We need to better understand how infectious fully vaccinated people who become infected are, as this will help to better predict the situation in the coming months, and our findings are contributing to a more comprehensive picture of this,’ he said.
The study, based on data collected between 24 June and 12 July, found the highest rate of infection was among young people aged 13–24 and the lowest in those aged 75 and over. Women were also found to have a lower risk of testing positive than men. Those identifying as Black were more likely to be infected compared with white people, as were people living in lower socio-economic neighbourhoods.
The study also cites an increasing number of breakthrough infections among the fully vaccinated (44% of the total), a statistic that is likely to reflect the level of vaccination in the wider population.
The latest data suggests around 73% of people aged over 18 in the UK have had two vaccine doses.
Professor Booy again stressed that more breakthrough cases are ‘no cause for panic’ as infection tends to be mild and there is a relative lack of transmissibility.
The CDC, meanwhile, said the Massachusetts outbreak reinforces the need for prevention strategies in public places. Last month, it reintroduced a recommendation for fully vaccinated people to wear a mask indoors in areas of high transmission.
‘Jurisdictions might consider expanded prevention strategies, including universal masking in indoor public settings, particularly for large public gatherings that include travellers from many areas with differing levels of SARS-CoV-2 transmission,’ the report concludes.
Professor Booy strongly agrees with that stance.
‘We should continue as a matter of course in communities observing easy-to-do social distancing and other personal protective measures like masks in crowds,’ he said.
‘You don’t just get vaccinated. You go on doing easy-to-do but effective multi-prong approaches.’
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Dr James Alistair David Freeman   5/08/2021 12:48:46 PM

With PCR for viral load and HIV/HBV/HCV the sample comes from a blood sample which is invariably well mixed.

With PCR for SARS-CoV2 the sample is inherently unreliable. I have had 2 COVID tests. In one the sample was anterior nasal. The other resembled a frontal lobotomy with scrubbing of the swab sufficient to bring a tear to my eye. The quantum of generic material on the second swab would invariably have been higher as would have been the viral load had there been one to find.

Given viral load has not been show to correlate to clinical illness it strikes me that the only value of this data is to anti-vaxers.

The way this has been reported should give us pause. It might have been more useful to run with this as the headline point....

Double vaccinated people are less likely than unvaccinated people of testing positive after being in contact with a COVID-19 case (3.84% vs 7.23%), the authors concluded

Dr Olga Pylypyak   5/08/2021 5:45:48 PM

I am struggling to get Pfizer vaccine. Over 100 patients on waiting list.
Many patients are happy to pay for vaccine.
I am happy to come on Saturday/Sunday to provide vaccinations. Is there any chance to get Pfizer vaccine for patients ?