DISCUSSION: Can we stretch existing Covid vaccines to inoculate more people? Experts are divided

Can we stretch existing Covid vaccines to inoculate more people? Is the world is using more vaccine than it needs to on each person immunized, depriving people in the queue of a chance to be protected? Helen Branswell STAT

With the global supply of Covid-19 vaccine still woefully inadequate, vaccine makers are scouring the pharmaceutical landscape for partners to ramp up manufacturing, and civil society groups are pressing politicians to waive intellectual property protections in a bid to spur still more production.

But what if there was a simpler way? What if current supplies could be stretched, to vaccinate more people more quickly? What if the world is using more vaccine than it needs to on each person immunized, depriving people in the queue of a chance to be protected?

Reducing the size of a vaccine dose is an approach that has been used successfully before and ought to be explored, some scientists argue.

Several times in recent years the World Health Organization has recommended “fractionation” — using partial or fractional doses when supplies of critical vaccines have been limited. When a dangerous yellow fever outbreak in Angola and the Democratic Republic of the Congo threatened to exhaust the world’s stores of yellow fever vaccine, the WHO instructed countries to use one-fifth of a normal dose in their emergency vaccination efforts. (Research done during that 2016 outbreak suggested the lower dose protected those who received it.) The WHO has also recommended use of fractional doses of inactivated polio vaccine and meningococcal conjugate vaccines during periods of scarcity of those shots.

The idea of splitting doses of Covid vaccines is not universally supported, however; a number of experts contend that the vaccines should be used in the dose size tested during clinical trials and cleared for use by regulatory agencies. That route offers the best protection for individuals who are vaccinated, they insist. “The problem where I’m coming from is you have to prove fractional dosing works,” said Larry Corey, who co-led design of the trials of the Covid vaccines supported by the U.S. government. That hasn’t happened yet.

But Ben Cowling, an infectious diseases researcher at Hong Kong University, believes that a public health approach — one that focuses on what’s best for whole populations, not individuals — is what’s needed in a pandemic. He and two colleagues, Wey Wen Lim, of Hong Kong’s Laboratory of Data Discovery for Health, and Sarah Cobey, an associate professor of viral ecology and evolution at the University of Chicago, argued the case for using fractional doses of Covid vaccine in a commentary in Nature earlier this week.

“Think of the lives that would have been saved” if manufacturers geared their research to finding the smallest possible dose that was protective when they were testing their Covid vaccines, Cowling told STAT in an interview about fractionation. ...