Study examined 1,497 full-vaccinated healthcare workers for breakthrough infections

By Angela Betsaida B. Laguipo, BSNAug 2 2021

As vaccination efforts against the coronavirus disease (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), continue globally, scientists and public health officials are dealing with the threat of breakthrough infections. Scientists call such cases "breakthrough" infections because the virus has broken through the protective barrier provided by the vaccine.

A new study published in The New England Journal of Medicine found that in a very small number of cases, people with breakthrough infections might suffer long-lasting COVID-19 symptoms.

Researchers at the Sheba Medical Center in Ramat Gan in Israel and the Harvard T.H. Chan School of Public Health in Boston revealed that although the BNT162b2 Pfizer-BioNTech COVID-19 vaccine is highly effective (94% efficacy), rare breakthrough infections carry an infectious potential and pose a unique challenge. Since these infections are mostly asymptomatic, they may increase the risk of viral spread to vulnerable populations.

Study: Covid-19 Breakthrough Infections in Vaccinated Health Care Workers. Image Credit: Roman Yanushevsky / Shutterstock

Vaccine efforts and breakthrough infections

To curb the spread of the virus, vaccination efforts have commenced in most countries. Currently, nearly 4.11 billion vaccine doses have been administered across the globe.

Since its rollout in late 2020 in Israel, the BNT162b2 messenger RNA (mRNA) vaccine by Pfizer-BioNTech has been highly effective in preventing clinically significant COVID-19.

However, vaccine recipients have experienced breakthrough infections in a small number of cases, a phenomenon described in other countries and health care institutions.

The study

In the current study, the researchers studied 1,497 vaccinated health care workers at the Sheba Medical Center in Israel. They identified breakthrough infections by conducting extensive evaluations of health care workers who developed symptoms or had known infection exposure. These included epidemiologic investigations, repeat reverse-transcriptase polymerase chain reaction (RT-PCR) assays, antigen-detecting rapid diagnostic testing (Ag-RDT), and genome sequencing.

The team also matched patients with breakthrough infections who had antibody titers collected within a week before SARS-CoV-2 detection, also called the peri-infection period, with four to five uninfected controls.

The neutralizing antibody titers in patients during the peri-infection period were lower than those uninfected controls. Higher peri-infection neutralizing antibody titers were tied to lower infectivity.

The study findings also revealed that among the vaccinated health care workers in the study, only 39 were infected despite being vaccinated. Of these patients, 19 percent developed symptoms that lasted for at least six weeks, also called long-COVID. The symptoms include fatigue, muscle pain, headache, and loss of smell and taste.

"Most breakthrough infections were mild or asymptomatic, although persistent symptoms did occur," the team noted.

The B.1.1.7 variant or Alpha variant was found in 85 percent of samples tested. Also, about 74 percent of patients had a high viral load at some point during the infection. However, of these patients, only 17 had a positive result on the Ag-RDT, and there were no secondary infections reported.

In a nutshell, the researchers concluded that among the fully vaccinated health care workers, the incidence of breakthrough infections with SARS-CoV-2 was tied to the neutralizing antibody titers during the peri-infection period.

"We found that the difference in the peak titers of neutralizing and IgG antibodies between cases and controls was more strongly associated with the risk of infection than the difference in the peri-infection titers," the team concluded.

COVID-19 global case

To date, there more than 198 million infections from SARS-CoV-2 have been reported globally. Of these, over 4.22 million have died due to the infection.

The United States reports the highest number of cases, reaching over 35 million, followed by India, with a staggering 31.6 million cases. The other countries reporting surging COVID-19 cases include Brazil with 19.93 million cases, France, with 6.2 million cases, Russia, with 6.2 million cases, and the United Kingdom, with 5.9 million cases.