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COVID-19 breakthrough cases more likely in people with lower antibody levels, study finds 

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People who have lower antibody antibody levels after receiving COVID-19 vaccines are more likely to suffer breakthrough cases, a new study finds.

Researchers from the World Health Organization partnered with Israeli scientists to find if there is a correlation between weak antibody responses post-vaccination and a risk of breakthrough infection.

While experts have long believed that people with weaker reactions to the vaccine have higher odds of breakthrough cases, there was little hard evidence to confirm it.

This study provides some insight into the link between antibody levels and breakthrough infections and shows why people with certain underlying conditions may need a booster shot.

Researchers found that breakthrough cases (red dots) were much more frequent among people with low antibody responses to the virus, and those with strong responses did not contract Covid

Researchers found that breakthrough cases (red dots) were much more frequent among people with low antibody responses to the virus, and those with strong responses did not contract Covid

Experts have long believed that stronger antibody responses make a person more protected from Covid, though data proving it did not exist until recently. Pictured: A man in Jerusalem, Israel, receives a shot of a COVID-19 vaccine

Experts have long believed that stronger antibody responses make a person more protected from Covid, though data proving it did not exist until recently. Pictured: A man in Jerusalem, Israel, receives a shot of a COVID-19 vaccine

‘Among fully vaccinated health care workers, the occurrence of breakthrough infections with SARS-CoV-2 was correlated with neutralizing antibody titers during the peri-infection period,’ researchers wrote. 

‘Most breakthrough infections were mild or asymptomatic, although persistent symptoms did occur.’

The study, published last month in the New England Journal of Medicine, was conducted using data from health care workers at Sheba Medical Center in Tel Aviv, Israel.

Like almost every other resident of the Middle Eastern nation, workers at the hospital were vaccinated with the Pfizer-BioNTech vaccine. 

Around 500 of the nearly 1,500 workers at Sheba Medical Center were included in the study.

Even if they were fully vaccinated, the medical center still tested employees that either were exposed to the virus or showed symptoms.

Many of the study’s participants also took an antibody test for researchers to determine how strongly their body responded to the vaccine.

Between mid-December and late April, 39 breakthrough cases were detected among the staff.

None of the cases required hospitalization and only one had a pre-existing condition that would leave them more vulnerable to the virus. 

Of the 39 patients, 22 had their antibody levels measured before they contracted the virus.

Researchers established a clear trend between those who tested positive and those who showed low antibody levels before their infection.

The vaccine was still providing some level of protection for those with lower antibody levels, though.

‘These workers included some who had been asymptomatic and thus who had infections that would not have been detected without the rigorous screening that followed any minor known exposure,’ researchers wrote.

‘This factor suggests that at least in some cases, the vaccine protected against symptomatic disease but not against infection.

‘However, no secondary infections were traced back to any of the breakthrough cases, which supports the inference that these workers were less contagious than unvaccinated persons, as has been reported previously.’

The study was conducted before the rise of the Delta variant, which experts believe that vaccinated people can transmit at the same level as unvaccinated people. 

Meanwhile, those who had stronger responses to the vaccine did not experience any breakthrough cases.

The implications of this study are important for people with certain pre-existing conditions that limit their bodies reaction to the virus, like cancer. 

It also demonstrates why health officials are so keen to roll out COVID-19 vaccine boosters. 

A person’s antibodies, whether naturally occurring through infection or from the vaccines, wane over time.

Booster shots can trigger a massive spike in antibody levels, though, and make someone near immune to infection.   

While the findings of the Israeli study only apply to the Pfizer vaccine, experts believe people who generate stronger antibody responses to the Moderna or Johnson & Johnson vaccine have more protection from the virus as well. 

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