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| Scientifically Speaking All that we know about the B.1.617 variant | | |
Anirban Mahapatra
As the second wave of Covid rages on, we now know that cases of B.1.617 (which was previously called “the double mutant variant” because of two concerning changes in the spike protein) are increasing. Another variant which is increasing is B.1.1.7, which was first identified in the United Kingdom.
B.1.1.7 spreads more efficiently than earlier types of the coronavirus and is now the dominant form of SARS-CoV-2 in many countries. B.1.1.7 also likely causes more severe disease. However, it is not considered an “immune escape” variant because reinfections are uncommon; vaccines still work, albeit with reduced antibody recognition.
Two other mutants, B.1351 (which was identified in South Africa) and P.1 (which was identified in Brazil) are concerning. They spread rapidly. The spike protein in these two variants is not recognised as well by current neutralising antibodies. They have been referred to as “immune escape” variants because reinfections are common and vaccines are less effective against them. Right now, there is reason to believe that B.1.617 is more infectious that the ancestral virus identified in Wuhan, and roughly similar to that of the B.1.1.7 variant. This assumption is based on the increase in cases in India and elsewhere, and the recent elevation of a particular type of this virus to a “variant of concern”.
Along with data on spread, we also have some initial results on how well the modified spike of B.1.617 infects cells. A preliminary study by Markus Hoffmann and colleagues (posted to the preprint server, bioRxiv) used a different virus covered with coronavirus spikes from B.1.617 to test for viral entry into cells. Viruses with the mutated spike can enter two kinds of cells more effectively than the viral spike of the original virus. But further studies are needed to corroborate these early results. Early work by scientist Pragya Yadav and team indicates that B.1.617 might be causing more severe disease, at least in lab animals. Certainly, it would fit with reports from doctors on the frontline. Entire families are getting sick in the second wave. Many, including those who are young and have no comorbidities, are succumbing. But whether this is because more people in general have been infected or because of actual biological changes in the variant is yet to be determined. None of this is good news. The not-so-bad news is that B.1.617 does not seem to evade the immune responses of polyclonal antibodies that attack different parts of the virus as much as originally feared, or indeed as much as the B.1.351 variant. In B.1.351, the changes to the spike can evade many times more antibodies raised after earlier infection or vaccination, causing a drastic reduction in vaccine-induced protection. In the past few days, new studies have shown antibodies found in sera of people who have been infected before, or have been vaccinated, can block the B.1.617 variant from entering cells. Very preliminary data is available for all major vaccine classes, namely, Pfizer’s mRNA vaccine (after one or two doses), AstraZeneca/Covisheld’s viral vectored vaccines after two doses, and Covaxin’s inactivated virus vaccine after two doses.
In one study, scientists did show that antibody recognition was reduced in half in B.1.617 compared to the original strain. In case of vaccination, two groups found fewer neutralising antibodies with B.1.617 after two doses of the Pfizer vaccine compared to the original virus. But even with such a drop, protection was not completely lost because these vaccines are excellent in stimulating a large number of antibodies. They still had enough of a buffer to cope with this variant, at least in the laboratory.
Some people in India have suffered from severe and critical Covid-19 even after being fully vaccinated. There are some heartbreaking stories, but we still don’t know how frequently this is happening and under what circumstances. The laboratory data we have so far indicates some vaccine protection, so this is likely rare. In the coming days, we will have more information on how well these observations correlate with effectiveness in the real world. |
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