COVID-19: About the Delta variant

The SARS-CoV-2 virus that causes COVID-19 has undergone genetic mutations over time as it adapts to humans, leading to the development of new variants of the virus. One of these new variants, the Delta variant, is swiftly becoming the dominant variant globally.

The Delta variant has spread rapidly worldwide and is now the main variant in many countries. It is the most transmissible variant, spreading a lot more easily than the original version of the COVID-19 virus and other variants.

How Delta is different from earlier variants

Science is telling us the Delta variant has a number of differences compared to earlier iterations of the virus. These differences mean that the Delta variant is a greater threat to the health of individuals who contract the infection and a greater challenge to contain the spread of the virus in an outbreak. For example:

  • Delta can cause people to develop more serious COVID-19 illness than other variants of the virus
  • People with a Delta infection are at higher risk of needing hospitalisation.
  • The chance of infecting others such as within your household or other contacts is very high because Delta is so transmissible. It is estimated that on average, one person infected with Delta may infect 5 or 6 other people. This is how Delta outbreaks in places overseas have grown so rapidly.
  • People with Delta infections seem to carry much more virus (have a higher viral load) and for a longer period of time than those infected with the original virus or other variants.
  • The time from exposure to the virus until first symptoms is shorter for the Delta variant. Some people may have no symptoms (asymptomatic) when infectious.  

How we can protect ourselves: vaccine effectiveness and health measures

Globally, and here in New Zealand, it is so important to stamp out any community outbreaks as quickly as possible and to ensure very high rates of vaccination.

Being fully vaccinated gives you a high degree of protection against Delta infection, and an even higher degree of protection against severe illness, hospitalisation and death. Evidence currently shows the effectiveness of two doses of the Pfizer vaccine against illness due to Delta infection is about 88% and the protection against hospitalisation due to Delta infection about 96%.

However, no vaccine is 100% effective so there is some chance that a vaccinated person may become infected with the Delta variant and may transmit the virus to other people. Taking other precautions will remain important in order to continue to protect our communities.

As well as vaccination, early detection of cases and swift contact tracing, as well as isolation of cases and contacts, will be critical due to the shorter incubation period of Delta.

It will also be important to continue to protect ourselves and our whānau and stop the transmission of the disease by following health habits such as:

  • Physical distancing of 2m where possible
  • Wear face coverings on public transport and indoors in busy places such as supermarkets
  • Keep indoor rooms well ventilated (eg, by opening windows and doors) where possible
  • If you feel unwell, stay home
  • If you show any symptoms, call Healthline and get a COVID-19 test
  • Keep a record of where you’ve been or scan in wherever you go using the COVID Tracer app and turn Bluetooth on your phone so you can be contacted if you have been near a case.

Further information on Delta and other variants of interest or concern may be seen on our Science News page, updated weekly. 

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