The dominance of the South African variant of coronavirus in Dhaka is a reason for concern, but experts said mass inoculation should go on although early studies suggested that the available vaccines are less effective against the variant.
Inoculation will reduce mortality and morbidity rates, they said.
There is no conclusive data in the world that says the Oxford-AstraZeneca vaccine, which Bangladesh rolled out on February 7, does not work against the SA variant, they added.
An icddr,b study, published on Wednesday, analysed 57 samples between March 18 and 24, and found 46 or over 80 percent infected with the same SA variant.
The samples were collected from 13 districts, the majority being from Dhaka.
A study in South Africa, published on February 7, found the AstraZeneca vaccine less effective against the variant. But it also said the vaccine helped reduce the risk of severity of the disease.
The World Health Organization on 15 February recommended that the AstraZeneca vaccine be rolled out, even in countries where the SA variant, also known as B.1.351, or other similar variants are circulating.
Prof Sayedur Rahman, chairman of pharmacology at the Bangabandhu Sheikh Mujib Medical University, said, "Although there are dilemmas, many countries across the world are using the vaccine. Since we don't have a choice right now, we have to make the best of the vaccine.
"Someone who has taken the vaccine has less risk of contracting the disease. The most important part is that it lowers the degree of severity of Covid-19."
Regardless of whether one has been inoculated or not, people must wear masks and maintain social distancing, because these are more effective than anything else.
Mushtaq Hossain, adviser to the Institute of Epidemiology, Disease Control and Research (IEDCR), said the clinical trial conducted in South Africa was not conclusive and had not been accepted worldwide.
"The observation is that this [Oxford] vaccine is less effective against the SA variant. But it is still very good in preventing a patient from becoming critically ill," he said.
It is scientifically evident that this vaccine works against all the variants, said the noted epidemiologist, "We are closely monitoring the situation and there is no reason to worry."
Bangladesh has inoculated 5.5 million people with the first dose of the AstraZeneca vaccine. The campaign for the second dose started yesterday. Many countries across the world are inoculating people against coronavirus with this low-cost vaccine.
The UK, SA, and Brazilian variants of the virus have spread all over the world in recent weeks, according to different studies.
These variants are said to be more transmissible and have gone through new genetic changes, which may impact clinical manifestation and vaccine effectiveness.
The SA variant was first detected in the Nelson Mandela bay area in October, 2020.
The Vaccines and Infectious Diseases Analytics (VIDA) Research Unit at the University of the Witwatersrand in Johannesburg on February 7 released findings on the effectiveness of AstraZeneca vaccine against the SA variant.
The results showed that a two-dose AstraZeneca vaccine did not protect against mild to moderate Covid-19 in case of the SA variant. The trial was conducted on 2,026 participants.
VIDA Executive Director Prof Shabir Madhi said, "This vaccine may still help protect high-risk individuals with co-morbidities from contracting severe Covid-19 disease, having to be hospitalised, mechanically ventilated, or dying."
A laboratory study suggests that the SA variant may reduce protective antibodies elicited by the Pfizer Inc/BioNTech SE vaccine by two-thirds, and it is not clear if the shot will be effective against the mutation, Reuters reported on February 18, quoting the two companies.
The study found that the vaccine was still able to neutralise the virus and there is no evidence that the variant reduces vaccine protection, the companies said.
US drugmaker Moderna said the actual efficacy of its vaccine against the South African variant is yet to be determined. The company has previously said it believes the vaccine will work against the variant, said the Reuters report.
"There was a small study in South Africa which showed the Oxford vaccine was less effective. But we do not have adequate data to reach a conclusion," Dr Mustafizur Rahman, senior scientist at the icddr,b, told The Daily Star yesterday.
"Irrespective of the vaccine's efficacy, we must follow the health safety guidelines. The virus mutates continuously and the scientists are updating the vaccines. We should not panic."