Coronavirus vaccine: Will we need a third dose of the Covishield (Oxford-Astrazeneca) vaccine? Here's what studies indicate

While the Oxford-Astrazeneca COVID-19 vaccine continues to be engulfed by controversies over its usage and limitations, it still is one of the most popular vaccines in use. Recent studies have also indicated that the vaccine is well-effective against the Delta COVID-19 variant, and promises an acceptable level of efficacy against the same.

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Surprisingly, the Oxford-Astrazeneca vaccine is also one vaccine that has been touted to serve the highest potent efficacy when delivered months apart, unlike what other vaccines have been seen to offer. The vaccine is currently administered 3-4 months apart, which has been clinically proven to mount the highest level of antibodies. These recommendations are currently in place in countries like India and the United Kingdom. Now, newer studies have indicated that further spacing out the vaccine doses, or allowing people to get a 'third' dose at least 10 months after the first one will lead to an enhanced immune response...

Could the third dose act like a potential booster dose? Or will the dosing gap be revised again? Here's what the latest studies have found...

(Image credit: Agencies)

Multiple studies conducted over the previous months have established that delaying the second dose of the Oxford-Astrazeneca vaccine delivers a stronger immune response and makes the vaccine work more effectively.

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According to newer clinical observations, a possible 'third' dose of the vaccine, which could be administered in a delayed manner will also work to boost the vaccine's immunity and efficacy rates against COVID-19. The study, which advocated the benefits of delaying follow-up doses was carried out by Oxford University, which is the lead group behind the development of the vaccine.

The clinical observations, interesting follow up studies established that of all vaccines, mRNA vaccines, such as the ones developed by Pfizer-BioNtech and Moderna may provide lifelong immunity against coronavirus with its regular dosing schedule.

While the Astrazeneca vaccine has been found to be well-effective against mutant strains and passes the WHO standards of vaccine safety, it mounts a less effective efficacy in comparison to other vaccines and offers fewer protective odds with just a single dose of the vaccine. However, the Oxford study, which has not been published yet, has observed that doling out a third dose of the vaccine offers a much-stronger immune response with vaccination and leads to a 'substantial' increase in antibodies which does not compromise immunity.

Interestingly, the study also found that the vaccine also offered similar rates of response and immune protection when the second dose of the vaccine was administered as many as 10 months later. Overall, the researchers have advocated for the administration of a third potential COVID-19 dose.

Apart from this, it has also been studied that the side-effects of the vaccine tend to be more well-tolerated, with lower incidents of side-effects being reported with the second and third vaccine doses.

The Oxford study, which hasn't been reviewed yet, is the first of a kind study on the use and workability of a third (additional) vaccine dose, which could also work as a booster shot of the vaccine.

While newer variants of concerns (VOCs) and mutant strains are coming into play, virologists and epidemiologists are increasingly pressing on the need for booster shots of COVID-19 vaccines so as to ensure that vaccine-generated antibodies, which will be a driving factor for herd immunity do not wane, and instead are capable enough to provide additional immune strength against deadlier virulent strains of the virus.

For example, while originally, the Oxford-Astrazeneca vaccine has been found to be over 81-90% effective against the Alpha variant (original SARS-COV-2 strain), the vaccine's efficacy was scaled down to 64-70% with the Delta strain (the first dose only offers 34% protection). With newer variants surfacing, the availability of a booster, or a third dose will offer some level of reassurance.

Secondly, researchers also agree that the observations advocating for better immune response with a further delayed shot will also offer a sigh of relief to countries facing vaccine shortages, or currently following delayed inoculation with the vaccine.

The efficiency rates proved by the third COVID-19 shot will also factor in hope for people with compromised immunity- the ones who have pre-existing conditions that lead to waning immunity or may not be able to mount sufficient antibodies, even with two doses of the vaccine.

The findings of the Oxford study are yet to be reviewed or published in a scientific journal. As pressing and promising the studies are, there are no national or global recommendations vouching for the same, and therefore, there is no current plan as to when a third vaccine dose for Oxford-Astrazeneca or any vaccine will be advised.

For that to happen, countries across the world, such as the 160 nations wherein the vaccine is being administered, will also have to considerably scale up the pace of vaccination drives to ensure that more and more people receive at least 2 doses of the vaccine.

As for now, even though some countries have objected to the use of the vaccine over blood clotting risk, the only dosing gap that will provide an efficient immune response is when the vaccine is administered 8-12 weeks after the first dose.