The latest data collected by Bloomberg reveals that more than 2.62 billion doses have been administered across 180 countries. And this amounts to 17.1% of the global population.
However many people are beginning to wonder how long that protection will last and uncertainties are surrounding the possibility of needing an additional dose of the COVID-19 vaccines to boost immunity over time.
Amid these uncertainties, World Health Organisation's chief scientist Soumya Swaminathan in an interview with Bloomberg on Sunday has said there is not enough information to either confirm or dismiss the requirement for a booster shot after vaccination against Covid-19.
"We do not have the information that's necessary to make the recommendation on whether or not a booster will be needed," Swaminathan told the news website. "The science is still evolving."
The WHO chief scientist added that calls for using booster shots were premature since, in most countries, those at a high risk of Covid-19 infection hadn't even been fully vaccinated.
Swaminathan told Bloomberg that WHO would look at data from countries that introduce the booster shot later in 2021 before issuing its guidelines.
When asked about mixing vaccines, she told Bloomberg that using two different vaccines seemed to generate a stronger immune response.
She cited data from the UK and Germany that showed the "mix-and-match" inoculation regimen caused more minor side effects compared to two doses of the same vaccine.
Swaminathan remarked that heterologous prime-boost combinations appear to spur a more robust immune response, leading to both higher levels of virus-blocking antibodies and the white blood cells that kill virus-infected cells.
About the concept of heterologous prime-boost, Swaminathan noted that it seemed to be working well and suggested that it might open up the opportunity for countries that have vaccinated people with one vaccine and now are waiting for the second dose they have run out of, to potentially be able to use a different platform vaccine."