Why vaccinated people are catching COVID

They are known as “vaccine breakthrough cases’’. And while they are rare, experts say they are to be expected because no vaccine is 100 per cent effective.

But the emerging issue poses significant implications for when and how Australia and other countries reopen international borders, particularly if new strains of the virus emerging in India and South Africa may be more resistant to first generation vaccines.

The good news? Experts say they also confirm the vaccine is working because in most cases the vaccinated people who get COVID don’t have symptoms and don’t get sick.

But there are concerns of thousands of vaccine breakthrough cases that are starting to pop up in the United States, where more than 115 million people are fully vaccinated.

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According to the Centre for Disease Control in the United States there were 9245 “vaccine breakthrough” cases as of April 26.

One-in-four of those people tested positive but never had symptoms.

But 132 people, or 1 per cent of the breakthrough infections, died. Twenty of those deaths were in asymptomatic people or probably not related to COVID-19.

Those that died were generally older or immunosuppressed making them more vulnerable to COVID.

In the Seychelles, a COVID outbreak in one of the most vaccinated regions on earth is also causing concern for world health experts.

More than a third of people who tested positive for COVID-19 in the week to May 8 had been fully vaccinated.

Epidemiologists warn it is only a matter of time before more so-called “vaccine breakthrough” cases are detected in Australia when international borders reopen.

University of Melbourne professor Tony Blakely explains it as basic maths. Even if a vaccine is 95 per cent effective, that still means as many as one-in-20 people who are vaccinated could still contract and spread the virus, even if they don’t get sick or die.

“If a vaccine is 90 per cent effective and the majority of your population is vaccinated, at some point you’re going to start seeing more cases in the vaccinated,’’ Prof Blakely told news.com.au.

“As you get more and more people vaccinated you will see more cases.

“No vaccine is perfect. But you’ve got much less chance of catching COVID and dying.”

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Indeed, earlier this month six overseas travellers who reported they were fully vaccinated have tested positive for COVID-19 while in hotel quarantine in Sydney.

It’s also a reminder to get both jabs, because experts say people who have had a single dose of a COVID vaccine and have never been infected are more vulnerable to catching COVID.

In recent days, the Oklahoma State Department of Health has identified 258 vaccine breakthrough cases.

CNN recently reported in one week, there were nine cases of COVID-19 in fully vaccinated members of the New York Yankees organisation.

Of those who tested positive, eight of those nine cases were asymptomatic. They were only picked up because of strict team testing protocols, raising the prospect that the numbers in the community could be higher.

“It’s preventing serious infections in those staff and players with the Yankees,” Dr Costi Sifri, an infectious disease physician and hospital epidemiologist at the University of Virginia, told CNN.

“Those infections that occurred, the so-called breakthrough infections, importantly were for the most part mild to moderate infections.”

Experts say the lesson is that the US and the world needs to do more research into the vaccine breakthrough cases.

US virologist Rick Bright recently told MarketWatch that more genomic testing was required.

“I’ve worked in pandemic response for decades. Every time something bad happens, we just never seem to appreciate that it’s going to happen and how bad it’s going to be,’’ he said.

“Every time we get through it, we always say, ‘We’re going to do all these things and make it better [and] make sure it never happens again.’ And we don’t do it. There’s this cycle of panic, and then regret, and then forget.

“We have the capability now to do the [genomic] sequencing, but we’re just not doing enough of it, and we’re just not doing it smartly.

“We need to look at those vaccine breakthrough cases.”