Questions on vaccine efficacy as Karnataka prepares to give second dose to healthcare workers

As many as 13,594 health workers in Karnataka will be eligible for a second dose of the Covid vaccine on February 13, day 28 of vaccination. However, questions are being raised on how effective the vaccine will be if the second dose is taken this early.

On February 10, the World Health Organisation (WHO), for the first time ever released interim guidance on the use of Astra Zeneca-Oxford University Covid vaccine (Covishield).

It said, “In light of the observation that two-dose efficacy and immunogenicity increase with a longer interdose interval, WHO recommends an interval of 8 to 12 weeks between the doses.”

As per Serum Institute of India too, the manufacturer of Covishield, vaccinating after four weeks will provide 53% efficacy as against waiting for three months that will provide 78% efficacy.

Health department officials say though the matter was raised with the Government of India in their video conferences, the Drugs Controller General of India has approved only a 0-28 day schedule for the two doses and the state is not at liberty to change this even if beneficiaries request for a later date.

An official working closely with immunisation programmes in the state told DH, “Even in WHO’s interim guidance issued on Wednesday, it says, the second dose should be preferably given after eight to 12 weeks of the first dose, but can be given after four weeks also.”

“The question of efficacy isn’t being addressed in the case of Covaxin as we don’t even have data on its efficacy. Yet, the second dose will be administered after four weeks. Once, the safety and the fact that the vaccine generates antibodies was established approval was given without waiting for any further data. The government’s focus now is only on preventing Covid deaths and reducing the severity of the disease, which a vaccine helps in reducing, notwithstanding efficacy rates,” he said.

Covid-19 technical advisory committee member Dr C N Manjunath, who is due for his second dose on February 19, said, “As per the manufacturer, the second dose taken later the better. But the state is bound to follow the protocol set by the union government. If the state starts obliging requests of health workers, which includes doctors in the know of efficacy rates, to reschedule the second dose for a later date, the entire vaccination programme will go haywire with targets spilling over to the next month.”

Currently, Covid vaccines have an expiry date of May with a shelf life of only six months, as manufacturers did not have a lot of time to check its stability.