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Quarter-dose of Moderna COVID vaccine still rouses a big immune response
A little bit of coronavirus vaccine goes a long way towards generating lasting immunity.
Two jabs that each contained only one-quarter of the standard dose of the Moderna COVID-19 vaccine gave rise to long-lasting protective antibodies and virus-fighting T cells, according to tests in nearly three dozen people1. The results hint at the possibility of administering fractional doses to stretch limited vaccine supplies and accelerate the global immunization effort.
Since 2016, such a dose-reduction strategy has successfully vaccinated millions of people in Africa and South America against yellow fever2. But no similar approach has been tried in response to COVID-19, despite vaccine shortages in much of the global south.
“There’s a huge status quo bias, and it’s killing people,” says Alex Tabarrok, an economist at George Mason University in Fairfax, Virginia. “Had we done this starting in January, we could have vaccinated tens, perhaps hundreds, of millions more people.”
The just-right dose?
In the earliest trial of Moderna’s mRNA-based vaccine, study participants received one of three dose levels: 25, 100 or 250 micrograms3. The top dose proved too toxic. The low dose elicited the weakest immune response. The middle dose seemed to offer the best balance: it triggered strong immunity and had acceptable side effects.
That 100-microgram dose ultimately became the one authorized for mass use in dozens of countries. But Moderna scientists later showed that a half-dose seemed to be just as good as the standard dose at stimulating immune protection4.
To find out whether a low dose might offer protection, scientists analysed blood from 35 participants in the original trial. Each had received two 25-microgram jabs of vaccine 28 days apart.
Six months after the second shot, nearly all of the 35 participants had ‘neutralizing’ antibodies, which block the virus from infecting cells, the researchers reported in a preprint published on 5 July1. Participants’ blood also contained an armada of different T cells, both ‘killer’ cells that can destroy infected cells and a variety of ‘helper’ cells that aid in general immune defence.
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doi: https://doi.org/10.1038/d41586-021-01893-0
References
Mateus, J. et al. Preprint at medRxiv https://doi.org/10.1101/2021.06.30.21259787 (2021).
Casey, R. M. et al. N. Engl. J. Med. 381, 444–454 (2019).
Jackson, L. A. et al. N. Engl. J. Med. 383, 1920–1931 (2020).
Chu, L. et al. Vaccine 39, 2791–2799 (2021).
Cowling, B. J. et al. Nature Med. https://doi.org/10.1038/s41591-021-01440-4 (2021).
Więcek, W. et al. Preprint at SSRN https://doi.org/10.2139/ssrn.3864485 (2021).
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