Younten Tshedup 

People who have been fully vaccinated against Covid-19 can still contract the disease. This is a reality, say experts.

So far, a total of 11 individuals who have received both the dose of Covid-19 vaccine in either of the regimens — homologous or heterologous — have been infected with the virus in the country. These cases are called ‘breakthrough’ infections.

A member of the National Immunisation Technical Advisory Group (NI-TAG), Dr Sonam Wangchuk, said that the fact that no vaccines are 100 percent effective meant there were always possibilities of people contracting the disease even after being fully vaccinated against a disease.

“A person is considered fully vaccinated against Covid-19 once he or she completes 14 days after receiving both the doses of the vaccine,” said Dr Sonam Wangchuk. “A breakthrough infection happens if a person contracts the disease after being fully vaccinated.”

He said that breakthrough infections are a possibility, not just in case of Covid-19 but in other infections, as well. “No Covid vaccines, or for that matter any vaccine we have today, are 100 percent effective. Meaning there is a certain percentage that shows people can be infected even after the vaccine.”

Dr Sonam Wangchuk said that of the 11 breakthrough cases in the country so far, eight had received vaccines in a homologous regime.

He explained that the efficacy of two AstraZeneca doses was about 63 percent compared to 86 percent in a homologous mRNA vaccination. “While there is no specific efficacy percent for a heterologous vaccination, in our case, where we provided a mRNA vaccine as the booster dose, the efficacy is expected to be equivalent to a homologous mRNA vaccination if not more. 

It will not be less than that.”

Therefore, he said that the reason why there was proportionately more people experiencing breakthrough infection among the homologous regime (both doses AstraZeneca) recipients, was because the efficacy was comparatively lower than the heterologous (mRNA booster) recipients.


Delta variant threat

One of the major reasons behind the breakthrough cases is the highly infectious Delta variant of the SARS-CoV-2 virus.

Dr Sonam Wangchuk said that the Delta variant of SARS-CoV-2 is the predominantly circulating variant today, which is highly transmissible with an infectivity rate more than eight. This means that a person infected with the Delta variant can transmit the infection to at least eight more people.

The Delta variant, Dr Sonam Wangchuk said, is also known for effectively escaping the immune response. “Because there is an ongoing infection triggered by the Delta variant in our community, we will see breakthrough cases.”

Vaccination is still effective and significant   

Although the country is recording a few breakthrough cases, the rate of infection is comparatively higher in those who remain unvaccinated or have received only a single dose of the vaccine, including children.

Dr Sonam Wangchuk said that when it comes to infection from the Delta variant of the SARS-CoV-2 virus, there is usually ‘very high’ viral load in the respiratory tract of the patient. “But in a vaccinated person, the viral load clearing from the respiratory tract is very fast. This means that the person can transmit the virus to others but only for a short duration compared to those who are unvaccinated.”

Irrespective of the breakthrough cases, he said that vaccines are still effective in preventing people from developing severe disease from the infection including hospitalisation and mortality. “In the US, the severity among breakthrough cases is very low — the hospitalisation rate is about 0.004 percent, and the mortality rate is about 0.002 percent.”

Dr Sonam Wangchuk said that even after being fully vaccinated, there are a few groups of people including those with pre-existing medical conditions and the elderly population who will not develop adequate levels of antibodies from the vaccine. “Some people in these groups will not have an immune system strong enough even after both the doses, making them more vulnerable to infection and severe disease.”

He added: “For these groups of population and our children who have not received the vaccines, it is of utmost importance that people follow Covid protocols at all times and get vaccinated.”

Edited by Jigme Wangchuk