An official panel in India on Thursday recommended that the gap between the two doses of the Covishield Covid-19 vaccine be extended to 12-16 weeks.
No changes were suggested in the dosage interval for Covaxin, the second of two vaccines in use in India at this time, which remains at four to six weeks, reports NDTV.
The panel - the National Immunization Technical Advisory Group - also said pregnant women could choose their vaccine and that lactating women would be eligible any time after delivery.
The NTAGI also advised those with proven SARS-CoV2 illnesses (the virus that causes the Covid-19 disease) should defer vaccination till six months after recovery.
These recommendations will be sent to NEGVA - the National Expert Group on Vaccine Administration - for approval before the changes and suggestions are implemented.
This is the second time in three months Covishield dosage intervals have been widened; in March states and UTs were told to increase the gap from 28 days to six-eight weeks "for better results".
The changes prompted a sarcastic swipe from Congress leader Jairam Ramesh, who flagged the ever-widening recommended interval between doses.
"First, it was four weeks for the 2nd dose, then six-eight weeks and now we are told 12-16 weeks. Is this because there are not enough stocks of the vaccines for all who are eligible or because professional scientific advice says so?" Mr Ramesh asked.
"Can we expect some transparency from the Modi government?" he added.
The widening of Covishield dosage intervals has been linked to increased efficacy of the vaccine.
A study published in international medical journal The Lancet on February 19 claimed a 26.2 per cent increase - from 55.1 per cent to 81.3 per cent - if doses were spaced 12 weeks apart.
However, recommended changes to intervals also come amid an acute shortage of doses as the manufacturer - Serum Institute of India - struggles to keep pace with demand.
Earlier today SII officials told the centre Covishield production will be increased to 10 crore doses - but only from August - and that June-July production "may also increase by some quantity".
India is struggling to contain a devastating second wave of Covid-19 infections and deaths, with daily numbers now over three lakh for more than 21 consecutive days. The flood of cases has brought the country's healthcare system to its knees, and stressed the need for rapid vaccination.
The national vaccination drive began on January 16 and over 17.5 crore doses have been administered so far, but vaccine coverage is still less than 2.5 per cent of the population.
With manufacturers Serum Institute and Bharat Biotech (makers of Covaxin) still struggling to match demand, states have been forced to look abroad for doses.
A number of them, including national capital Delhi and Maharashtra, Kerala and Karnataka - three of the worst-affected - have floated global tenders for direct import of vaccines.
Serum Institute and Bharat Biotech have submitted to the Centre their production plan for the next four months, informing they can ramp it up to 10 crore and 7.8 crore doses respectively by August, official sources said on Wednesday.