Top 3 COVID-19 vaccine questions – Rapid COVID-19 tests, herd immunity and what causes virus to change

Department of Health

Top 3 news

Top 3 - Michael Kidd

8:13

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Hello and welcome to today’s Top Three. My name is Michael Kidd, I’m the Deputy Chief Medical Officer here at the Department of Health in Canberra. I’m very pleased to be joined today by my friend Linda. Firstly, my shout out today is to people in Australia who donate blood. At the moment, we have a shortage of blood supplies in our blood banks across Australia, and it is very important that people are continuing to make blood donations, obviously blood donations save lives right around Australia. If you are a regular blood donor or if you are thinking about making a donation for the first time, now is a good time to go to your local blood bank and make a donation. And indeed in most of our states and territories, even if you are in lockdown, travelling to make a donation is one of the reasons why you may be allowed to leave your home. And so to our top three questions.

The first question today is: how many people need to be vaccinated against COVID-19 in Australia in order to achieve herd immunity?

Now, we hear a lot about herd immunity and at the moment we actually don’t know how many people will need to be vaccinated in order to achieve herd immunity in Australia. Herd immunity is when we have had either enough people exposed to a disease or vaccinated against a disease to prevent further transmission of the disease occurring among other people and particularly people who are not able to be vaccinated. In Australia this includes newborn babies, it includes people who may be immunocompromised and at the moment, of course, with COVID-19 it includes anyone under the age of 16 years because we don’t yet have vaccines which are registered and available to children in Australia. With some other diseases herd immunity can occur when up to 60% or 70% of the population has been immunised against serious infectious disease. But we don’t know if that rate is going to be enough to protect people against COVID-19 and especially as new variants of COVID-19 continue to appear around the world, variants which may be more easily transmissible or may cause more severe disease. So we are still learning a lot about herd immunity from research being carried out in Australia and overseas, but I don’t have a definitive answer to the question about what actual percentage of people need to be vaccinated before we get herd immunity in this country.

The second question is: what causes the COVID-19 virus to change?

The virus which causes COVID-19 can undergo small changes in its genetic make up, as it is transmitted from person to person. Usually these changes which occur in the virus are not significant and they do not cause any change in the way the virus behaves. But sometimes we can get changes which can lead to the virus becoming more transmissible or even the virus being able to cause more severe disease, and when this occurs, we describe that new variant of the virus as being a variant of concern. And the current Delta variant of the COVID-19 virus, which is occurring in Australia at the moment and has led to the current lockdowns across the country, is one of these variants of concern. The other thing we can do with the testing is we can actually do genomic sequencing of the virus from different people. And because of these slight changes in the virus we can actually determine who infected who, and this can be very helpful when we are following up the contact tracing and when we are following up the sources of outbreaks of COVID-19 occurring across Australia. It does though reinforce the importance of vaccination, because the more people who are vaccinated against COVID-19, the less opportunity the virus has to change and for these new variants to start appearing. Vaccination helps to protect us all against both infection with COVID-19 but also against the possible developments or development of these variants of concern.

The third question is: how do rapid COVID-19 tests differ from other tests?

You may have heard a bit about rapid tests for COVID-19 being developed both in Australia and around the world. At the moment, the gold standard test in Australia is the PCR test, and if you have been tested for COVID-19 in Australia, chances are that you have had a PCR test. This is the test we are familiar with: you have a swab put in the back of your throat and a swab in the back of your nose, and then the swab is sent off and tested for the presence of the COVID-19 virus in those swabs. The advantages of these PCR test is that they are very accurate, and so if someone has a positive result with one of the PCR tests, then that person is highly likely to have been infected with COVID-19. If we do a test and it is too early in someone’s course of infection, even with the PCR test, we may get what is called a false negative test and if we retest that person in two or three days they will have a positive test. That is why it is important if you have been exposed to COVID-19 and you have been told to isolate and get tested, that you follow the instructions of the public health authorities in your state or territory. The rapid tests, which are being developed, have an advantage in that they can give a result within 15 to 20 minutes of the test having been carried out. The challenge with the test is that they are not quite as accurate as the gold standard PCR test. This means there is the risk that someone may have COVID-19 but may have a negative result or someone who does not have COVID-19 may have a positive result. And it is very important when we are dealing with outbreaks like we are dealing with at the moment that we actually can have total confidence in the tests which we are carrying out. And so that is why we continue to use the PCR tests. The rapid test though may start to have more utility as the pandemic changes, particularly if we are doing daily tests of people in certain industries or in certain situations, but it remains to be seen how these test are going to be used during the pandemic in Australia. And that’s our Top Three for today. Thank you for joining me. And always thank you to Linda.

Top 3 questions

  1. How do rapid COVID-19 tests differ from other tests?
  2. How many people need to be vaccinated for Australia to achieve herd immunity?
  3. What causes the COVID-19 virus to change?

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