Don't Go For Boosters Now

The priority should be the 2-dose mission. Fewer fully vaccinated means higher chance of variants

- K Srinath Reddy

Covid vaccines were developed, trialled and delivered for mass immunisation in less than a year after the genomic sequence of SARS-CoV-2 virus was identified. This boosted confidence that the pandemic could end through mass vaccination. As high-income countries stepped up vaccination in early 2021, the main global concern was related to gaping inequities in vaccine availability across countries. With efficacy rates in trials far exceeding the pre-set regulatory threshold of ‘50% protection against Covid-19 disease’, the whole world competed for the vaccines.

That upbeat feeling dissipated when ‘breakthrough infections’ were reported in increasing numbers among the fully vaccinated. Recent reports from Israel were particularly disappointing, as the country had become a poster child of a quick return to pre-pandemic norms of an open society after speedy vaccination. However, there was reassuring news from the UK and elsewhere that full vaccination is substantially protective against severe disease and death. People were reminded that systemically administered vaccines were expected to protect against ‘disease’ and not viral ‘infection’ perse.

The advent of the Delta variant changed the dynamics of viral transmission among vaccinated persons. Not only was it infecting fully vaccinated persons, mostly with mild clinical effects, but viral loads in the upper respiratory tract were observed to be as high among the vaccinated as in the unvaccinated. Continued use of masks and avoidance of super-spreader events appear necessary in countries where the Delta variant is in active circulation, even if their populations were widely vaccinated before Delta crossed their borders.