It’s Delta today, and even Delta-plus, but new variants of the novel coronavirus won’t end there. As it becomes evident that vaccines based on the genetic blueprint of earlier variants can be less effective — although experts are quick to clarify that shots already out all provide some level of protection — against newer avatars of the novel coronavirus, scientists have got to work tweaking the existing doses to take on the evolving threat. Here’s what that takes.
How Have New Variants Affected Vaccine Performance?
Earlier this year, reports said that South Africa had decided against using doses of the Oxford-AstraZeneca vaccine that it had procured from the Serum Institute of India because it had found that the shot was not very effective against the Beta variant of the novel coronavirus that was circulating in the country.
The variant, first identified in South Africa in May last year, has been designated as a Variant of Concern (VoC) by the World Health Organisation, which means it has been found to demonstrate increased transmissibility and reduce the “effectiveness of public health and social measures or available diagnostics, vaccines, therapeutics".
Several manufacturers, including AstraZeneca, are working on tailor their vaccines to counter the Beta variant.
India, where the Delta variant triggered a massive surge of cases in the second wave of Covid-19 eralier this year, has observed a decline in effectiveness with two of the frontline vaccines — Covaxin and Covishield — being used in the country. Reports say the Indian Council of Medical Research (ICMR) has found that there was a three-fold reduction in the effectiveness of Covaxin, the inactivated virus vaccine made by Bharat Biotech, against the Delta variant while Covishield — which is the name under which Oxford-AstraZeneca’s viral vector vaccine is being used in India — showed a 2-fold drop against it. The mRNA vaccines being okayed for use in US — made by Pfizer-BioNTech and Moderna — too, have shown lower impact against Delta.
However, experts have been at pains to point out that decline in efficacy is not a zero-sum game and all vaccines still provide sufficient protection against newer variants, although they were designed to target the earliest versions of the virus. Thus, even if breakthrough infections — the term for cases where a fully vaccinated person contracts Covid-19 — are seen to be on the rise, vaccination almost certainly protects against hospitalisation and death.
How Do Vaccines Suffer Loss In Effectiveness?
All the vaccines that are being used to tackle the novel coronavirus target the spike protein on its surface, which the virus uses to invade and enter human cells. The spike protein is an automatic target for vaccine makers, who are looking for tactics to train the body’s immune system to recognise and attack the virus. However, the spike protein is a slippery customer and constantly keeps undergoing mutations.
Alterations in the placement of the spikes make it tougher for vaccines to target them by triggering the production of antibodies. These neutralising antibodies are designed to prevent infection. But such antibodies are not the only protection that vaccines offer. There are also T and B cells that the body produces to ward off disease and these are seen as providing a long-term shield against the virus.
How Easy Is It To Tweak Vaccines?
That depends on the vaccine platform and then there are regulatory steps to go through as well. But tweaking vaccines is nothing new. The flu vaccine is updated every season to keep up with changes the virus takes on from one year to the next. There is a proper surveillance mechanism anchored by the WHO for tracking and selecting the annual tweaks to the flu vaccines.
According to Gavi, which is pursuing equitable distribution of vaccines globally, some vaccines are fairly easy to tweak while updating the more traditional ones can be time consuming. The mRNA vaccines, like the ones made by Pfizer-BioNTech and Moderna, work by inserting genetic information into human cells to nudge them into producing the spike protein of the novel coronavirus, which the immune system then attacks by producing antibodies against it. To tweak such vaccines, all scientists have to do is swap out the earlier genetic code of the spike protein with the genetic make-up of the new variants.
Vaccines like the one made by Astra-Zeneca can be a little more tough to upgrade but the company is already working on a newer version of its shot that specificall targets the Beta variant.
It is significant that regulatory authorities may not insist on large-scale clinical trials as they had for the first versions of these vaccines and — much like it is for the seasonal flu vaccines — seek only safety data from smaller trials.
Further, new vaccines are in the works that target not only the spike protein but other genetic locations of the novel coronavirus. Called multivalent vaccines, these shots can be designed to target elements from multiple variants to create something of an all-round dose against the novel coronavirus.