Experts have stressed the need for including all aged 50 and above in the priority list for the first phase of Covid-19 vaccination to maximise the effectiveness of the inoculation campaign.

Besides, they have suggested a longer gap between the administration of the first and second shots, arguing that it will make the vaccine more efficient. 

The government is set to roll out its coronavirus vaccination programme in the first week of next month. It has purchased 3 crore shots of the Oxford-AstraZeneca vaccine, branded Covishied, from Serum Institute of India, and plans to vaccinate 1.5 crore people in the first phase.

The first consignment of 50 lakh doses is expected to arrive next week, and online registration for the campaign starts on January 26.

Ahead of the inoculation campaign, the government has prepared a priority list, in which frontline health and social-care workers, along with different other professionals, have been included. The list also includes people aged 64 and above, and those under 65 with comorbidity. 

Officials of Directorate General of Health Services said they prepared the priority list in line with guidelines from the World Health Organisation, a scientific advisory group of experts and taking the current context of the country into consideration.

But experts said people aged between 50 and 63, especially in the Covid-19 red zone districts, should also be vaccinated in the first phase, considering the current Covid-19 situation. They said it would save lives.

DGHS data show more than 80 percent of those who died after contracting the virus in the country were aged over 50, and more than half of the deceased lived in Dhaka, Chattogram, Narayanganj and Gazipur.

Among the 7,950 dead so far, more than 25 percent or 1,994 people were aged between 51 and 60. Of the total 529,687 Covid positive cases, 11 percent belonged to the 51-60 age group, shows the IEDCR website, which contains data of till January 18.

"The existing vaccination plan of the government is good. But maximizing the outcome should be the key. For doing so, the government should include those aged 50 and above in the priority list," Prof Sayedur Rahman Khasru, chairman of pharmacology at the BSMMU, told The Daily Star.

"If we can administer a single dose on those from the most vulnerable age groups in the risky zones, it will protect them, resulting in fewer deaths and infections," he said.

Dr Mushtuq Hussain, a consultant at the IEDCR, said the vaccination plan could be modified considering the availability of vaccines. "The WHO's scientific conference [on Friday] advised the authorities to vaccinate the people with higher risks  and in the infection-intensive areas if the number of vaccine doses are limited."

He also said with fewer vaccine shots in hand, the government should be open to inoculating people who came in contact with any positive cases.

"This is called ring vaccination which was applied during the smallpox inoculation campaign," said Mushtuq.

Infectious disease expert Prof Ridwanur Rahman too opined that people aged 50 and above can be included in the priority list.  "People aged 50 and above can be included in the priority list, if there are necessary supplies. If supplies are limited, the people with comorbidity should get priority," he told The Daily Star on Tuesday.

Health Minister Zahid Maleque told reporters on Thursday that the government had decided to increase the minimum age limit for the vaccination to 50 in the priority list.

But a DGHS official, preferring not to be named, said the minister actually asked to include people from the 50-63 age group in vaccination campaign, subject to the availability of eight lakh Pfizer vaccines from the Covax.

Bangladesh is supposed to get 6.8 crore vaccine shots from Covax, a global vaccine alliance. But the authorities have said the country's existing cold chain system cannot support the ultra-sub-zero vaccines like Pfizer which are needed to be stored at temperatures below -70 degrees Celsius.

Dr Shamsul Haque Mridha, line director of Maternal Neonatal Child and Adolescent Health at the DGHS, said they were still not considering to include people aged between 50 and 63 in the priority list for the first phase.

"They are not included in the first list of 1.5 crore people," he said.

Shamsul, however, said everything would depend on the availability of the vaccines. "We cannot say right now how many doses we will get, apart from those from Serum."

He said a total of 50 lakh people -- drawn from 18 professional and age categories -- would get the first dose of Oxford-AstraZeneca vaccine in the first month. The second dose would be given eight weeks after the first shot.

Prof Sayedur Rahman, however, recommended increasing the gap to 12 weeks or more from eight weeks.  "We will get only 3 crore doses of vaccine in the next six months. If we go for the single-dose policy, we can protect more people. The UK has extended the interval between two doses to 12 weeks. It means they want to give protection to more people -- even if it is for a few months."

Financial Times newspaper of England has reported that extending the interval could give better immunity in case of Oxford vaccines.

Data from the Oxford/AstraZeneca trials also showed that antibody levels were nearly three times higher in participants who had waited 12 weeks between doses, compared with those where the gap had been under 6 weeks.