COVID-19 vaccination begins across Australia. Health authorities are therefore keen to dispel myths about the vaccines, including any impact on COVID testing.
Do the vaccines give you COVID, or do you test positive for COVID? Does the vaccine affect other tests? Should we still have COVID tested if we have symptoms, even after we’ve had the chance? And will we still need COVID testing once the population is vaccinated again?
We look at the evidence to answer five common questions about the impact of COVID vaccines on the test.
Read more: Do I have to register for a COVID vaccine? How will I know when it’s my turn? Questions about vaccines answered
Will the vaccine give me COVID?
The short answer is no”. This is because the vaccines approved so far in Australia and elsewhere do not contain any live COVID virus.
The Pfizer / BioNTech vaccine contains an artificially generated portion of viral mRNA (messenger ribonucleic acid). It contains the specific genetic instructions for your body to make the coronavirus’ “peak protein”, against which your body provides a protective immune response.
The AstraZeneca vaccine uses a different technology. It packs viral DNA into a viral vector ‘carrier’ based on a chimpanzee adenovirus. When you deliver it to your arm, the DNA asks your body to produce the ear protein, which in turn stimulates an immune response.
Any side effects from vaccines, such as fever or fatigue, are usually mild and temporary. These are signs that the vaccines are helping to improve your immune system, rather than signs of COVID itself. These symptoms are also common after routine vaccinations.
2. Will the COVID vaccine make me test positive?
No, a COVID vaccine does not affect the results of a COVID diagnostic test.
The current gold standard diagnostic test is known as nucleic acid PCR testing. It is looking for the mRNA (genetic material) of SARS-CoV-2, the virus that causes COVID-19. It is a marker of current infection.
This is the test that the vast majority of people have when they stand at a door-to-door test clinic, or visit a COVID clinic in their local hospital.
Yes, the Pfizer vaccine contains mRNA. But the mRNA it uses is only a small part of the entire viral RNA. Nor can it make copies of itself, which would be necessary to be in sufficient quantity to be traced. It can therefore not be detected by a PCR test.
The AstraZeneca vaccine also contains only part of the DNA, but is placed in an adenovirus carrier that cannot repeat, and it cannot give you infection or a positive PCR test.
Read more: How Pfizer and Moderna mRNA vaccines work, why it’s a breakthrough and why it should be kept so cold
3. How about testing for antibodies?
While PCR testing is used to look for current infection, antibody testing – also known as serological testing – records past infections.
Laboratories check if your immune system has produced antibodies against the coronavirus, a sign that your body has been exposed to it. Since the antibodies take time to develop, it can be positive to test with an antibody test that you were infected weeks or months ago.
But your body also produces antibodies in response to vaccination. This is the way it can recognize SARS-CoV-2, the next time it does, to protect you from severe COVID.
When COVID vaccines are rolled out and people develop an antibody response through vaccine, it can become difficult to distinguish between someone who has had COVID in the past and someone who was vaccinated a month ago. But it depends on the serology test used.
Read more: Antibody tests: in order to catch coronavirus, we need to know who has had it
The good news is that testing for antibodies is not nearly as common as testing for PCR. And it is ordered only under limited and rare circumstances.
For example, if someone tests positive with PCR, but it is false positive due to the characteristics of the test, or if fragments of virus linger in the respiratory tract due to an old infection, public health experts may request an antibody test to see if that person has been infected in the past. They can also order an antibody test during contact detection of cases with an unknown source of infection.
Read more: Why can’t we still use antibody tests to diagnose COVID-19?
4. If I get vaccinated, should I have another COVID test if I have symptoms?
Yes, we will continue to test for COVID as long as the virus is circulating all over the world.
Although the COVID vaccines look promising to prevent people from becoming seriously ill or dying, they do not offer 100% protection.
Real-world data suggests that some people who are vaccinated can still get the virus, but they usually get only a mild illness. We are not sure if vaccines will be able to transmit it to others, even if they have no symptoms. It is therefore important that people keep testing.
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Furthermore, not everyone is eligible to receive a COVID-19 vaccine. In Australia, for example, current guidelines exclude people under 16 and those who are allergic to vaccine ingredients. And although pregnant women are not excluded from receiving the vaccine, it is not regularly recommended. This means that part of the population will remain susceptible to catching the virus.
We are also not sure about the effective vaccines against emerging SARS-CoV-2 variants. We will therefore continue to test to ensure that people are not infected with these strains.
Read more: UK, South African, Brazilian: a virologist explains each COVID variant and what it means for the pandemic.
We know that testing, detecting new cases and contact detection are the core components of the public health response to COVID and will continue to be a priority from a public health perspective.
A minimum number of daily COVID tests are also required so that we can trust that the virus is not spreading in the community. New South Wales, for example, aims for 8,000 or more tests a day to maintain this peace of mind.
Continued vigilance and high tests for COVID will also be important as we enter the flu season. This is because the only way to distinguish between COVID and flu (or any other respiratory infection) is through testing.
5. Will the testing of COVID stop as time goes on?
It is unlikely that our approach to COVID testing will change in the immediate future. However, as COVID vaccines are rolled out and as COVID is likely to become endemic and remain with us for a long time to come, the acute reaction phase to the pandemic will end.
COVID testing can therefore become part of the management of other infectious diseases and part of the way we respond to other ongoing health priorities.
Read more: Coronavirus can become endemic – this is how