The decision to increase the interval between Covishield doses based on scientific evidence

New Delhi: Dr. NK Arora, President, COVID-19 Working Group of the National Technical Advisory Group on Immunization (NTAGI) i.e. National Immunization Technical Advisory Group, interacted with Doordarshan on the COVID-19 vaccination campaign in India.

Increasing the interval between two doses of Covishield based on scientific evidence

Dr. NK Arora said that the decision to extend the interval between two doses of Covishield is based on the basic scientific reasons for the response to Adenovector vaccine. Under this, the interval of 4-6 weeks between doses has been increased to 12-16 weeks. He said, “In the last week of April 2021, the ‘Public Health’ of England released the figures. This organization is the official agency of the Department of Health. These data showed that if the interval between two doses is increased to 12 weeks, the vaccine effect is between 65 and 88 percent. On this basis, they controlled the epidemic spread due to the alpha variant. The UK managed to come out of the pandemic because it maintained a 12-week gap between the two doses. We also thought it was a good approach, because we had enough basic scientific reason to suggest that when the interval is extended, the adenovector vaccine works better. Hence, the decision to increase the interval between two doses to 12-16 weeks was taken on May 13.” He further said that space has also been left for people in this, because not every person can come for the second dose at exactly 12 weeks.

Emphasizing on this fact, Dr. Arora said that the decision to increase the interval between two doses of Covishield has been taken on the basis of scientific evidence. He said, “We have a very open and transparent system where decisions are taken on scientific basis. The Kovid Working Group has taken this decision unanimously. There is no difference in this. After this, every detail of this issue was discussed in the meeting of NTAGI. There was no difference here either. It was then recommended that the interval between two doses of the vaccine should be reduced to 12-16 weeks.”

Dr. Arora said the earlier four-week decision was based on the trial data available at that time. Citing examples, he said that the decision to increase the interval between two doses is based on studies that show that increasing the interval increases the effectiveness of the vaccine. He said, “The results of the initial study on Covishield were very mixed. When the Covishield vaccine came out in December 2020, some countries, such as the UK, decided to have a 12-week gap between doses. We had access to these data. When we had to decide on the interval, we decided to make the interval four weeks based on a bridging trial (which takes into account the genetic composition of the particular breed). It gave good results. Later we got more scientific and experimental data. These data showed that the potency of the vaccine increases further after six weeks. Then we came to the conclusion that the interval should be increased from four weeks to six weeks. The data during that period showed that when the interval is of four weeks, the effect is about 57 percent and by eight weeks, 60 percent.

When asked why the NTAGI had not already made the interval 12 weeks, Dr. Arora said, “We had decided that we should wait for the basic data from the UK (the second largest user of the Astra-Zeneca vaccine) “

He also said that there is precedent for Canada, Sri Lanka and some other countries, which are giving two doses of Astra-Zeneca vaccine between 12-16 weeks. Astra-Zeneca is the only Covishield in India.

Single-dose versus two-dose protection

Dr. Arora said that there was evidence and reports coming in about the effect of taking only one dose of the vaccine and taking two doses. NTAGI was also looking into this issue. He said, “When we decided to increase the interval between doses, 2-3 days later there were some reports from the UK that a single dose of Astra-Zeneca provides 33 percent protection. When two doses are taken, 60 percent protection is provided. From mid-May onwards, there was discussion on whether India should re-impose the gap of four or eight weeks or not.

He also said that it was decided to create a tracking platform to assess the impact of the vaccination programme. He said, “When NTAGI took this decision, we also decided that India would also create a vaccine tracking platform, so that not only the effectiveness of the vaccination program was assessed, but the vaccine type and the interval between doses and the entire Or what is the effect on people who are partially vaccinated, it can also be evaluated. This is very important in India, because in our country about 17-18 crore people have taken only one dose, whereas about 40 million people have received both the doses.”

Dr. Arora mentioned a study by PGI, Chandigarh. In this, a comparative study of the effect of partial and complete vaccination has been done. He said, “The study of PGI, Chandigarh clearly states that when one dose of vaccine and two doses were administered, the vaccine was 75 percent effective in both the cases. In this way, it was found that at least in the short term, the effect of the vaccine is the same, whether it is given in one dose or both. The study was quoting from the Alpha variant, which moved to Delhi after wreaking havoc in Punjab, North India. It also meant that even if you had only one dose, you were still protected.”

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