While the time gap between Covishield’s first and second dose has come under the scanner yet again, Public Health Foundation of India (PHFI) president Srinath Reddy in an exclusive interview to The Hindu said Indian experience on the issue is still being gathered. “There are reassuring reports of good protection being provided to healthcare workers. However, it is not yet clear how effective one dose is against the Delta variant, which is the dominant variant now in many parts of the country. We still need that data, especially for high risk older age groups,” he said. He said India has not vaccinated enough numbers as yet. “There are many susceptible individuals still,” Dr. Reddy said.
The time gap between Covishield’s first and second dose has come under the scanner in India yet again. Should we be reverting to a shorter time gap?
The time gap issue initially surfaced due to the way the AstraZeneca trials were conducted internationally. The British-led international trial accidentally created two strands among the trial participants — a larger group which received the vaccine shots at a 4-week interval (as per trial protocol) and a smaller group which received the second shot after 12 weeks. Interestingly, the second group showed higher efficacy (81%).So, Britain decided to adopt a 3-month dosing interval. A later large U.S. trial of the same vaccine, with 32,000 participants, also showed a high efficacy (76%). The WHO recommended an 8-12 week spacing.
Those trials were conducted when the ancestral wild virus was in circulation. Then came the variants, against which most vaccines showed lower efficacy. Even then, the first dose of the AstraZeneca vaccine offered adequate protection against the Alpha variant. Against the Delta variant, however, the first dose provided only 30% efficacy against symptomatic infection, according to recent data from Public Health England.
Against serious illness and death, the vaccine seems to provide reasonable protection with one dose. A second dose demonstrably increases efficacy against both mild and severe infections. Hence, the U.K. switched to an 8-week interval. Concerns have been raised about inadequate protection of a single dose against the Delta variant, in a French study. Two doses do provide better protection. Hence, the suggestion from international experts that the people at risk of severe disease must be provided that level of protection early rather than late.
Indian experience is still being gathered. There are reassuring reports of good protection being provided to healthcare workers. However, it is not yet clear how effective one dose is against the Delta variant, which is the dominant variant now in many parts of the country. We still need that data, especially for high risk older age groups and persons with co-morbidities — not just in relatively younger and healthier healthcare workers.
I would like to close this by pointing out the National Technical Advisory Group on Immunisation (NTAGI) has stated it will review recent evidence. Let us leave it to that expert body, to review all available national and international evidence. In the meanwhile, people need to be assured that vaccines are protective even against the delta variant. They should get both shots, whenever scheduled. If there is a limited supply till July, let us use the available vaccines to provide maximum protection to the most vulnerable. There is no reason for vaccine hesitancy. Let both scientists and media focus on building vaccine confidence. That will serve India best.
Has India vaccinated enough of its population? Is the pace of vaccination steady enough to allow opening of the country?
We have not vaccinated enough numbers as yet. There are many susceptible individuals still. I believe the pace of vaccination will pick up from July, with increasing domestic production and international procurement. I think we do need to open the country, but carefully. Vaccines protect against disease, once the virus infects. For protection against viral transmission, we need to adhere to public health advisories, with discipline in our behaviour for several months more. We must wear masks, avoid ill ventilated and crowded places as much as possible and not allow super-spreader gatherings. Safe behaviours and vaccines will together protect us. We can’t run fast on one leg.
Is there enough data to start children’s vaccination?
International trials are available for some mRNA vaccines, to provide evidence of efficacy and safety. Trials in younger children, some including even infants aged six months, are now in progress. Some trials of child vaccination are now on in India too. We should wait for these international and domestic trials to be completed. If a nasal or orally administered mucosal vaccine proves safe and efficacious, that will be a boon for child vaccination.
Are the mutating virus a cause of worry? Is there data showing that virus could escape vaccination cover?
The worry is misplaced at present. Available vaccines are offering enough protection, at the right dose. Even if neutralising antibody levels fall with time, T-cell immunity is likely to remain. In fact, that cell mediated component of our immune system is capable of fighting the virus which has entered our cells, whereas antibodies can only attack the surface spike protein as it circulates in the blood. Memory T and B cells also store the image of the antigen and can readily reactivate our defence when the virus enters our body.
Newer vaccines are also being prepared and some are under testing. Current mRNA vaccines are being tweaked to attack the spike protein mutations in the variants. Inactivated whole virus vaccines are being prepared, similar to Covaxin. Beyond that, multi-antigen vaccines are being tested, which combine the spike protein, the nucleocapsid (which wraps the genetic material of the virus) and ORF 3a (which helps the viral replicas to exit the infected cells). Such vaccines will present a larger platter of our antigens to our immune system. Even if spike protein mutations evade the neutralising antibodies, other antigens in the vaccine will still evoke an effective response. These internal antigens of the virus are also much slower in mutating than the surface spike protein. So, science can still provide us solutions.
What is the way ahead?
We need to combine four components of response as we move ahead. They are: (1) protect ourselves from exposure to the virus and its entry into the body; (2) Prevent free passage of the virus by avoiding crowded places, non-essential travel and super-spreader gatherings; (3) vaccinate as fast and as many as possible, across the country and (4) develop, evaluate and introduce new vaccines which can effectively protect against current and emerging variants.
