COVID-19 vaccination | Longer inter-dosage interval may offer better immunity

By Special Correspondent

COVID-19 vaccination with an inter-dosage interval of 10-14 weeks elicits a stronger immune response than when the vaccine is delivered at an interval of 4-6 weeks, a study done amongst a closely followed patient cohort in Kochi has reported.

The difference in immune response, when the interval between shots is extended, is more than three-fold. The longer the gap between the two shots, the higher the levels of anti-spike protein antibody response produced. This essentially means that two doses of vaccine delivered at a longer interval is likely to give stronger and longer-lasting immunity against COVID-19, says Padmanabha Shenoy, a clinical immunologist and rheumatologist at Kochi, who led the study.

The study to measure the immune response was conducted recently in a group of 213 patients, from amongst a cohort of 1,500 patients with autoimmune rheumatic diseases, who were vaccinated and regularly followed up.

The patients, in their 50s, were grouped into those who took Covishield vaccine at a gap of 4-6 weeks (102) and those who received the same but at a dosage interval of 10-12 weeks (111). The anti-spike antibody levels were measured in both groups a month after the second dose.

The antibody levels were found to be 255 in the first group, while it was 879 in the second group.

The data are important as there are not many studies measuring the immune response derived from Covishield. The results from a study at the University of Birmingham with Pfizer vaccine had similar data, says Dr. Shenoy.

“In Israel and the U.S., Pfizer vaccine was administered at an interval of three weeks while the U.K. had extended this interval to 4-6 weeks. It is probably because of the shorter interval and waning immunity that Israel had to go in for the booster doses,” he says.

While a longer interval between doses gives longer individual protection, one also stands the risk of contracting COVID infection in between this long gap.

Earlier studies have shown that a single dose of Covishield provides only about 33% protection against the Delta variant. Thus there has always been this confusion whether the inter-dosage interval should be reduced so that both doses can be administered at a faster pace, reducing the chances of people contracting COVID in between doses.

It thus seems to be a trade-off between the options, early but short-term immunity or a late but long-term immunity.

“The study answers the question, what is the ideal inter-dosage interval when it comes to vaccination using Covishield. An interval of 8-10 weeks between the doses will be ideal and a gap less than that might not give the individual adequate protection against COVID-19,” Dr. Shenoy said.


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