The government on Wednesday approved Biological E's Corbevax as a precaution dose for those above 18 years fully vaccinated with either Covishield or Covaxin.

This is for the first time that a booster dose that is different from the one used for primary vaccination against Covid has been allowed in the country.

All necessary changes in administration of heterologous precaution dose using Corbevax to those eligible and due for precaution dose have been made on the Co-WIN portal. This provision would be live from August 12, Union Health Secretary Rajesh Bhushan said in a letter to states and Union territories.

He said that Corbevax will be available as precaution dose after completion of 6 months or 26 weeks from the date of administration of the second dose of either Covaxin or Covishield vaccines for population above 18 years.

"This enables use of Corbevax as a heterologous COVID-19 vaccine for precaution dose administration in this age group," Bhushan said.

There will be no change in existing guidelines for homologous precaution dose administration of Covaxin and Covishield, he said.

In addition to the existing homologous precaution dose, the option of a heterologous precaution dose with Corbevax would be available to all persons above 18 years of age.

The decision has been taken based on scientific evidence, global practices and the recommendations of domain knowledge experts.

"Instruction in this regard may be issued to all concerned officials and it may also be publicised widely. I look forward to your support and leadership in achieving high coverage of precaution dose to all due beneficiaries at Covid vaccination centres during the ongoing 'Covid Vaccination Amrit Mahotsav' campaign," Bhushan said in the letter.

India's COVID-19 vaccination program has achieved the historical milestone of administering more than 2 billion doses so far.

About 97 per cent of the 12 plus age population of the country has been covered with at least one dose and about 89 per cent with both doses. Considerable progress is also being made under "Covid Vaccination Amrit Mahotsav" (from 15 July to September 30), to cover eligible beneficiaries above 18 years with precaution dose, he said.