The Monday after the federal election, my phone rang and the dreaded message popped up: “I’m so sorry Call. I have COVID.”
It came from a friend and just 36 hours before that we were sitting in her living room eating cheese and watching the polls.
Since election night was a classic, chilly Melbourne autumn night, her windows were closed and the heating was on high.
After marinating for over four hours in that virus hotbox, I was sure my COVID-free run was over and I would test positive soon too.
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After returning a questionable RAT result, I went out to do a PCR test… which came back negative.
This was not the first time I had close contact with someone with the disease and sailed on, seemingly untouched†
I’ve had three doses of COVID-19 vaccine, but Omicron seems to be bypassing even those after a few months.
That got me thinking: Have I already had COVID-19 and just didn’t know?
Estimates vary for the proportion of infected people who show no symptoms, but Omicron, which has the dominant variant in Australia this year, seems to provoke more asymptomatic infections than previous variantsso it wasn’t out of the realm of possibility.
So I went to my GP, who referred me for a blood test.
How do I know if I’ve had COVID-19?
PCR tests and RATs can tell you if you are currently infected with the SARS-CoV-2 virus, which causes COVID-19, but only a blood test can tell you if you have been infected in the past.
My blood sample was sent to a lab, where it was analyzed for vaccine-generated antibodies and actual infection.
The difference between the two comes down to what our immune system “sees” and what it responds to.
Approved COVID-19 vaccines in Australia work by activating our immune system to make antibodies against the spikes coming from the SARS-CoV-2 virus sphere.
An infection, on the other hand, triggers a much broader immune response. It generates antibodies against proteins that make up the virus sphere, called the nucleocapsid, as well as its spiny bits.
If a lab test picks up high enough levels of nucleocapsid protein antibodies, that’s a pretty good sign of a previous infection.
It’s a different story for people vaccinated with, say, China’s Sinovac or Sinopharm vaccines, said Dorothy Machalek, a senior research associate and epidemiologist at the Kirby Institute who coordinates blood tests to detect SARS-CoV-2 infection in Australia.
These are whole virus vaccines and contain killed or inactivated copies of the whole SARS-CoV-2 virus.
This means our bodies make antibodies against the bulb and spikes, Dr. Machalek says, making it “virtually impossible” to distinguish between an immune response generated by vaccination with the whole virus and one from infection.
What Can a COVID-19 Antibody Test Tell You?
Blood tests for antibodies can tell you if you’ve had COVID-19, but there are some caveats.
COVID-19 antibodies naturally decrease over time† so if they show up in your blood test, their levels can’t tell you exactly how long ago you were infected — just that you were infected sometime in the past few months.
“We’re Thinking Now” [the test] is a useful indicator of a fairly recent infection, as opposed to whether you’ve ever been infected,” says Dr Machalek.
A negative result does not necessarily mean that you have never had COVID-19. You may have had it too long before there were any antibodies left.
“If you want to know if you were infected after the introduction of COVID in Australia in March 2020, there really is no way to test that.
And if you have a positive result – show that your blood contains antibodies generated by COVID infection – that does not necessarily mean that you are protected against reinfection.
That’s because not all antibodies are created equal: just some will “neutralize” or prevent a viral infection from spreading throughout our body.
“Of some pathogens, like hepatitis B, if your antibodies are above a certain threshold, you can say you have a level of protection,” says Dr. Machalek.
“The general [tests] that we use for large-scale surveillance studies also won’t tell you which variant you have, but you can do additional tests that can give you an indication.”
And because blood tests for antibodies only measure antibodies, they can’t provide information about possible longer-term immune protection, such as types of B cells and T cells, which can help and defend us, even if our original stock of antibodies is gone.
Why large-scale blood surveillance?
These kinds of tests aren’t just for curious people like me. They are used to monitor infections on a much larger scale.
And there’s a chance my sanguine juices, taken during a regular old blood donation at Lifeblood, were included in an ongoing Australia-wide COVID-19 antibody study led by Dr. mahalek†
Earlier this year, the study analyzed blood from more than 5,000 donors. It found that at least 17 percent of Australian adults were infected with COVID-19 in early March and had enough antibodies to show up on tests.
The team, from the National Center for Immunization Research and Surveillance and the Kirby Institute, has just finished collecting samples for the next round of results, said Dr. Machalek.
They will hopefully have another report by the end of July.
Seeing how COVID-19 infections change over time, captured by such “sero-surveys,” provides insights not necessarily captured by reported data, and thus is a “key piece of pandemic intelligence,” she adds. .
“We can use the results of the latest serosurvey to plan for what we are seeing now in terms of the increase in cases and the potential impact that could have on hospitalizations and deaths.
“We know there is widespread community transmission, but we need to continue to understand how widespread it is.
My results came back a few days later
So I haven’t had COVID-19 – so far, at least not this year.
That was a real surprise to me.
I have spike protein antibodies in my blood, but very few nucleocapsid protein antibodies.
Maybe I’ve been incredibly lucky, or maybe I’m one of the few who is genetically resistant to COVID-19†
My GP had a more pragmatic answer: “Those are your vaccines that work.”
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