Dialog Box

How effective are the vaccines against the Delta strain?

Dr Emily Isham is a GP with qualifications in Women's & Children's Health, and Public Health.

Before Delta, the increasing global data caused most doctors and scientists to be cautiously optimistic that COVID-19 vaccines would cut SARS-CoV-2 transmission by half. But now,  with the development of new variants, Delta appears to be spreading in both unvaccinated and vaccinated people.   

Studies coming out of the UK, Singapore and the USA are showing that vaccinated people who become infected with the Delta strain of COVID-19 can carry and shed the virus like unvaccinated people – in other words, they have virus particles in their noses and throats, and can transmit it unknowingly to others. These are called “breakthrough infections”.  

So what is the point of getting vaccinated against COVID-19?  

We know, however, that even though people who are vaccinated can get breakthrough infections and carry virus in their noses and throats, they carry less virus, and their viral loads decrease much more quickly. This means that vaccinated people who are infected aren’t contagious for nearly as long as those who are unvaccinated and infected, according to researchers in Singapore.  

We can also see from very good data right around the world that, although the vaccines don’t work quite as well as they did against the original Alpha strain, they continue to protect from severe disease, hospitalisation and death when it comes to the Delta strain. In fact, if you get infected with Delta COVID-19 after having two doses of either AstraZeneca or Pfizer BioNTech vaccines, your disease will be milder, shorter, and your risk of needing hospital and dying from COVID-19 is reduced by 95-96%.  

We need to adapt to a world where we live with COVID-19 and it doesn’t overwhelm the health system, so our goal is to stop hospitalisations and deaths and vaccines can help us to do this.  

Getting vaccinated also contributes to wider herd immunity, and the quicker we build a herd immunity “wall” around the community, the less likely more variants will develop. Herd immunity means that the virus is less likely to grab hold within a community, and the chain of transmission will be more disrupted, meaning that those who are vulnerable will be protected, including those who have cancer or who have previously been on cancer treatment.  

How can we stay protected?

All of this points to the need for continued protective measures, even when vaccination targets are reached, and especially so those in our cancer community who are immunocompromised or otherwise vulnerable can stay safe.  

We’ve already discussed the need for those who have cancer or have previously been on cancer treatment to get vaccinated, however, until we have better data on transmission and long-term immunity, and until we have assured access to vaccine boosters, those people need to continue behaving like they haven’t been vaccinated for added protection – wearing a mask, especially indoors, maintaining good hand hygiene, physical distancing here possible, and isolating if COVID-19 positive.  

References:  
  • Brown, C. M. et al. MMWR Morb. Mortal. Wkly. Rep. 70 1059–1062 (2021) 
  • Musser, J. M. et al. Preprint at medRxiv  https://doi.org/10.1101/2021.07.19.21260808 (2021) 
  • Chia, P. Y. et al. Preprint at medRxiv  https://doi.org/10.1101/2021.07.28.21261295 (2021) 
  • Riemersma, K. K. et al. Preprint at medRxiv  https://doi.org/10.1101/2021.07.31.21261387 (2021)
02 September 2021
Category: News
Tags: Cancer, cancer and covid, Coronavirus, COVID, covid and kids, Covid-19, delta strain, Rare, Rare Cancer, Rare Cancers Australia, sars-cov-2, vaccine, young people and covid,
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