More than two years since COVID-19 was detected in Malta, an increasing number of people are questioning their immunity, after contracting the virus multiple times.

Sarah Carabott asked epidemiologist NEVILLE CALLEJA: are some more susceptible to it than others?

COVID mutation over the past months, coupled with a waning immunity among the older population, increases the risk of reinfection, according to Calleja, who told Times of Malta this risk could be mitigated with vaccination.

Earlier this week, Superintendent of Public Health Charmaine Gauci reassured people that studies about reinfections were ongoing.

Still, many are questioning their own immunity after contracting the virus more than once. One reader said he tested positive for the virus three times in just 18 months, despite being vaccinated.

Although the first time the symptoms were not too heavy, and it felt more like a bout of flu, by the second time around he also developed a fever that lasted for some days.

When contacted, Calleja said the risk of reinfection had increased considerably by the time the Omicron variants surfaced.

Danish and UK data suggests that by March 2021, those who had contracted COVID had a 20 per cent chance of contracting the Delta variant. In the UK, the risk of being infected with Omicron is now 5.4 times more likely than it was with Delta.

“The risk of reinfection tends to be heavily influenced by the variants involved. It is evident that exposure to a specific COVID variant does not guarantee protection from a different variant. 

“Recent Danish research also confirmed that reinfection with the BA.2 variant has also been observed among individuals previously infected with the original Omicron (BA.1),” Calleja added.

The same Danish researchers have also observed that vaccinated people are less at risk of reinfection. This has been corroborated also by various other studies, including the US Centers for Disease Control and Prevention.

Needless to say, immune escape still happens, even with vaccines, but it appears to be much likelier with natural immunity- Epidemiologist Neville Calleja

“This makes sense as vaccines are inherently designed to provoke an immune response to various specific parts of the viral particle, with a view to reduce the risk of immune escape as much as possible. 

“Needless to say, immune escape still happens, even with vaccines, but it appears to be much likelier with natural immunity.”

Additionally, vaccines are tested to ensure that the required immune response does happen in those who are vaccinated. This is not necessarily the case with natural infection. 

“It has been documented that the milder the infection, the less the generated natural immunity and, consequently, the less the immune protection against future COVID infection,” he said.

That said, there are other factors affecting immune response in general, not just against COVID, Calleja added. 

Immune protection is known to be lower in those aged 65 and over, which complicates further the known phenomenon of waning immunity for coronaviruses in general – be it natural immunity or vaccine-induced immunity. This also applies to those who are immuno-suppressed.  

The same March 2021 Danish data estimated that less than 50% of the 65+ recovered population was protected against reinfection with the Delta variant, as opposed to just under 80% at whole population level.

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