Unvaccinated, Omicron-infected individuals vulnerable to reinfection

Unvaccinated individuals show only very weak antibody responses to Omicron infection and may be susceptible to reinfection, while vaccinated individuals develop robust and broadly reactive antibody responses against SARS-CoV-2 variants, researchers from the University of Hong Kong (HKU) and the Chinese University of Hong Kong (CUHK) have reported.

“Omicron caused the fifth wave of COVID-19 in Hong Kong. This variant acquired novel mutations in its spike protein and allowed breakthrough infection in vaccinated individuals … BA.2 appears to have even higher transmissibility than BA.1,” wrote the researchers. “It is of public health importance to assess how well existing vaccines [ie, BNT162b2 and CZ02] protect against BA.2.”

In the study, the 50 percent plaque reduction neutralization test (PRNT₅₀) was used to correlate the protection against SARS-CoV-2 infection. The findings showed that in unvaccinated individuals, BA.2 infections induced only very weak antibody responses to BA.2 (ie, low PRNT₅₀ titre of ≤80), with little cross-neutralization, indicating that they may be susceptible to infection by BA.1 or other variants. [Euro Surveill 2022;doi:10.2807/1560-7917.ES.2022.27.18.2200178]

“In contrast, a breakthrough infection caused by Omicron [BA.1 or BA.2] in fully vaccinated individuals leads to a more potent antibody response, which is [at least] six times higher than the response in unvaccinated COVID-19 patients,” the researchers highlighted. “More importantly, such an antibody response found in vaccinated individuals is broadly reactive … implying that individuals with [vaccine] breakthrough infections have broad cross-immunity to SARS-CoV-2 variants [such as Beta, Delta, and BA.1].”

“Do not assume that an Omicron infection alone in unvaccinated individuals can induce strong immune protection against future variants,” said Professor David Hui of the Department of Medicine and Therapeutics, CUHK. “These patients are highly recommended to get vaccinated after full recovery from infection [ie, ≥1 month after the infection].”

HK’s first clinical trial of novel oral COVID-19 treatment

The fifth wave of COVID-19 in Hong Kong saw a death toll exceeding 9,000, with the majority being elderly or patients suffering from chronic conditions. “New variants will constantly emerge and spread in our community. Therefore, we need new treatment options that can help prevent progression to severe illness and complications, especially in [these] vulnerable populations,” said Dr Andrea Luk of the Department of Medicine and Therapeutics, CUHK.

In view of this, CUHK is conducting Hong Kong’s first clinical trial of a novel oral treatment specifically developed for COVID-19. The drug, known as JT001 (VV116), is for early treatment of COVID-19 in patients with mild-to-moderate infection. In the study,  a total of 2,000 adults with recently confirmed COVID-19 will be recruited from CUHK and other study sites in China. Study participants will be randomized to receive JT001 (VV116) or placebo for 5 days, and closely observed for disease progression for up to 29 days, to evaluate the effectiveness of JT001 (VV116) in preventing progression to severe illness. [NCT05242042]

Previously, JT001 (VV116) has been shown to reduce viral load and inflammation in the lungs of infected animals, and has demonstrated a good safety profile in phase I clinical studies in healthy volunteers.

“We hope that the research data can be used by the Hospital Authority as a reference to provide more options for clinical treatment of COVID-19 patients in the future,” said the researchers.