A new study shows that people who have lower levels of antibody after receiving COVID-19 vaccinations are more likely than others to develop breakthrough cases.

Researchers from the World Health Organization worked with Israeli scientists in an effort to determine if weak antibody responses following vaccination are linked to a higher risk of breakthrough infections.

Experts believe that people with weaker reactions to vaccines are more likely to have breakthrough cases. However there was not enough evidence to support this belief.

This study gives some insight into the relationship between antibody levels, breakthrough infections, and why people with certain underlying conditions might 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 discovered that breakthrough cases (red dots), were more common in people with low antibody responses to HIV than those with strong immune responses.

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 believed for years that stronger antibody responses are more effective in protecting against Covid. However data to prove this was not available until recently. Pictured: A COVID-19-vaccinated man in Jerusalem, Israel receives a shot

Researchers found that breakthrough infections with SARS-CoV-2 were more common among fully vaccinated health workers. This was in correlation with the presence of neutralizing antibody levels during the periinfection period. 

“Most breakthrough infections were mild to asymptomatic, but 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.

The Pfizer-BioNTech vaccine was administered to all employees at the hospital, just like every Middle Eastern citizen. 

The study included 500 of the approximately 1,500 workers at Sheba Medical Center.

Even though they had been fully vaccinated the medical center still tested any employees who were either exposed to the virus or were showing symptoms.

Many participants took an antibody test to help researchers determine how strong their body was responding to the vaccine.

From mid-December to late March, 39 breakthrough cases among the staff were discovered.

None of these cases required hospitalization. Only one case had a pre-existing condition which would make them more vulnerable to the virus. 

22 of the 39 patients had their antibody levels tested before contracting the virus.

Researchers found a clear trend in the proportion of those who tested positive for antibodies versus those with low levels before they were infected.

However, the vaccine still provided some protection for those with lower levels of antibody.

‘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 suggests that the vaccine protected against symptomatic diseases in some cases but not against infection.

“However no secondary infections were traced back from any of the breakthrough patients, which supports the conclusion that these workers were less infectious than unvaccinated individuals, as has been previously reported.

The study was completed before the emergence of the Delta variant. Experts believe that vaccinated individuals can transmit the virus at the exact same rate as unvaccinated. 

However, those with stronger immune responses to the vaccine did NOT experience breakthrough cases.

People with certain pre-existing conditions, such as cancer, that limit their body’s reaction to the virus are advised to read this study. 

It also shows that health officials are eager to distribute COVID-19 vaccine boosters. 

Over time, antibodies in a person’s body, whether they are naturally acquired from infection or from vaccines, decrease.

Booster shots can cause a huge increase in antibody levels and make you nearly 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.