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Our current understanding of COVID-19 infection leads us to believe that people who've recovered from the virus end up developing natural immunity.
What's not known about post-infection immunity is precisely how long it lasts, assuming that it is indeed finite. However, past observations of some recovered COVID-19 patients tell us that re-infection can occur, with some people being infected twice.
This indicates that natural immunity can actually weaken over time.
Experts now believe that people who have previously been infected with COVID-19 should get at least one vaccine dose.
They say it's a reasonable precaution.
IMAGE: Reuters / Nikkei Asia
"In a way, we are regarding the actual infection as the first dose of a vaccine, therefore only one jab is needed," said Dale Fisher, senior infectious disease consultant at Singapore's National University Hospital.
This recommendation comes as Singapore announces that every person who has recovered from COVID-19 will be given priority for a single vaccine dose, given that they've waited more than six months post-infection. It's believed that within the six months following infection, the person's immune response will still be quite strong – strong enough to defend against another infection.
And encouragingly, as of July 15, more than 51,000 people who previously recovered from COVID-19 received their allotted single vaccine dose.
IMAGE: Reuters / World Economic Forum
There may even be a slight advantage for previously-infected people who get a vaccine dose – a similar or higher level of neutralizing antibodies compared to uninfected people with two doses. But this only applies to people who have taken mRNA vaccines, namely Pfizer and Moderna.
Interestingly, previously-infected people who receive a second vaccine dose don't end up developing anymore protection from it, no more than the first dose, according to observations by Hsu Li Yang, infectious disease specialist at the National University of Singapore's Saw Swee Hock School of Public Health.
Hsu also notes that people who have recovered from COVID-19 end up developing varying levels of immunity. That means some individuals may be conversely more or less immune, depending on their own bodies.
There's no unified agreement among health experts globally about whether recovered patients should get both doses, or just one.
For example, countries like France and Italy are in agreement with Singapore in that recovered patients are only recommended to get one dose. On the other hand, the U.S. is of the opinion that recovered patients should get both doses, as soon as they can.
IMAGE: AFP / New Straits Times
Singapore, with its single dose recommendation, has a few reasons why it's asking people to wait at least six months after infection before getting their jab.
One reason people are being asked to wait that long is the possibility of immune exhaustion. If people get their jab too soon after infection, experts believe there won't be enough "fresh immune cells" to respond to the vaccine. Giving the body enough time to develop these immune cells is key to maintaining a high level of immunity, according to Asia Pacific Society of Clinical Microbiology and Infection president Paul Tambyah.
At the same time, people might face the risk of immune enhancement, which is the phenomenon that occurs when "an already primed" immune system overreacts to a vaccine.
Do you think recovered COVID-19 patients should get one or two doses, if at all?
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Cover image sourced from Reuters / The Straits Times and Hari Anggara / Malay Mail.
