Two landmark studies show that double-jabbed people infected with the Delta variant can spread the virus as easily as unvaccinated individuals. Early exploratory findings from Public Health England reveal that the Delta strain causes a similar viral load in the population, regardless of vaccination status. So an infected person sheds the same amount of virus when coughing or sneezing, whether they’ve had two doses or none. 

Related research from the University of Oxford reveals you’re less likely to catch COVID if vaccinated, but it’s still possible to pass the virus to others. In the largest-ever study into vaccine effectiveness against the Delta strain, Oxford scientists found that two doses of the Pfizer vaccine cut your chances of contracting COVID by 82 per cent, while the Astra Zeneca vaccine was 67 per cent effective. The Pfizer vaccine wore off more rapidly, however. 

Is herd immunity now impossible? 

The studies stress that COVID-19 vaccines provide significant protection against death and hospitalisation. But – crucially – they also indicate that herd immunity could be unachievable. 

Professor Sarah Walker, Professor of Medical Statistics and Epidemiology at the University of Oxford and Chief Investigator and Academic Lead for the COVID-19 Infection Survey, said: 'The hope was the unvaccinated people could be protected by vaccinating lots of people… [but] the higher levels of virus that we're seeing in these infections with vaccinated people means unvaccinated people are going to be at higher risk.’

Dr Simon Clarke, a microbiology professor at Reading University, commented on the research: ‘We'll need more studies to find a definitive answer. But if the vaccine only blocks transmission by, say, 50 per cent, you'll never get herd immunity even with a 100 per cent vaccine uptake.’

Businesses must build new safety nets

The findings should trigger an urgent call to action for employers. When government eased mandatory safety restrictions earlier this summer, many businesses pinned productivity hopes on staff vaccinations and eventual herd immunity. The new research shows we can no longer depend on these defences. Unless companies implement their own COVID controls, they’ll remain in the current, costly cycle of disruption and downtime. 

Regular workforce testing gives companies a way out. By using twice-weekly screening to identify positive cases, you can halt transmission risks before they lead to outbreaks, staff absence and self-isolation requirements. 

Screening also fights the dangers of false security. Believing they’re fully protected from the virus, vaccinated people can easily write off common Delta variant symptoms – such as headache, sore throat and fatigue – as a harmless cold. That’s on top of one in three COVID-19 carriers showing no signs of the illness at all. A rolling testing programme singles out asymptomatic cases, so work can continue in a reliably risk-free environment. 

Simpler testing solutions are now available 

With the burden now on businesses to track risks within their team – whether workers have had their jabs or not – companies need simple, cost-effective testing tools. Fortunately, screening has evolved at pace since the start of the pandemic. 

With saliva-based lateral flow tests, such as KnowNow, staff can now comfortably self-screen at home using a single cheek swab. Workers receive a 100% accurate result within 15 minutes. As part of a wider biosecurity solution, test outcomes are loaded into a purpose-built app, generating a unique QR code. The code is scanned upon entry to your workplace, so you can be confident only non-infectious employees are heading onsite. 

After 18 months of uncertainty, the revelation that Delta can be transmitted by vaccinated staff is another blow for businesses. It’s confirmation that – without a clear route to collective immunity – COVID is with us for the long term. Proactive employee testing helps companies regain control and continue moving forward.  

Take a closer look at KnowNow  

The UK-made KnowNow test can detect positive COVID cases as early as day three to four of infection: the point when staff are most likely to pass on the virus. Screening is simple, speedy and non-invasive – and in more than 258 clinical tests, KnowNow has never produced a false positive. 

Learn more at knownow.com.