`All of them are healthy, have no Covid-19 symptoms, no fever, no cough, no sore throat, no loss of taste, no loss of smell, psychologically stable,` said Dr. Nguyen Van Vinh.

Common symptoms of Covid-19 are fever, cough, and difficulty breathing.

According to Dr. Chau, these 55 employees have been fully vaccinated with two doses of AstraZeneca’s Covid-19 vaccine.

The Hospital for Tropical Diseases is coordinating with the Oxford University Clinical Research Unit to monitor the clinical progression and virus levels of these positive employees to evaluate the effectiveness of the vaccine.

The military sprayed and disinfected the entire Ho Chi Minh City Tropical Diseases Hospital on the afternoon of June 13.

To date, almost no country has published specific, large-scale, long-term studies on vaccine effectiveness against new strains, except statements from manufacturers.

Since the beginning of 2021, emerging variants have become a challenge to the global vaccination program.

To date, preliminary studies show that Covid-19 vaccines generally recognize variants, but effectiveness is significantly reduced when exposed to the virus.

There are a number of reasons why vaccine-induced immunity recognizes the variant but does not protect against it.

Current key vaccines such as Moderna, Pfizer, and AstraZeneca react differently to each nCoV variant.

The AstraZeneca vaccine is prepared using vector technology, using a harmless cold virus (adenovirus) from chimpanzees, cultured in the laboratory.

According to data from AstraZeneca, the vaccine is 76% effective in reducing the risk of symptomatic disease, meaning the risk of vaccinated people getting Covid-19 is 76% lower than that of non-vaccinated people.

Research published in February in the UK showed that the vaccine was 74.6% effective against the Alpha variant, but decreased effectiveness when encountering the Beta variant.

For the Indian Delta variant, two doses of the vaccine were 60% effective.

The Pfizer vaccine is prepared using mRNA technology, carrying genetic information of nCoV into the body, instead of the original inactivated or reduced virulence virus.

A vial of Pfizer’s Covid-19 vaccine is used in the US.

On April 2, Pfizer announced final-stage trial results showing that the vaccine is 95.3% effective, preventing even severe cases of nCoV infection.

In early May, Pfizer announced that the vaccine was 95% effective in preventing severe or fatal disease in people infected with the Alpha and Beta variants.

Like the Pfizer vaccine, the Moderna vaccine uses mRNA technology.

According to research by New York University School of Medicine and NYU Langone Center, USA, the Moderna vaccine is still highly effective against the Delta variant.

To date, the number of people using the Moderna vaccine is much smaller than AstraZeneca and Pfizer.

Johnson & Johnson (J&J) vaccine is prepared using vector technology, similar to the AstraZeneca vaccine.

In South Africa, vaccine protection dropped to 64% due to the circulating Beta variant.

In Ho Chi Minh City, according to Dr. Chau, experts are closely monitoring and studying more closely the effectiveness of the vaccine on 55 medical staff infected with Covid-19 despite having received two full doses.

According to the Ho Chi Minh City Center for Disease Control (HCDC), the screening results of 107 F1 family members of positive cases detected 7 positive cases, the remaining are still negative.

Le Phuong – Thuc Linh