The race to develop a vaccine against novel coronavirus infection is worldwide and involves several different strategies.

In a Harvard University press release, Ofer Levy, MD, PhD, professor of pediatrics at Harvard Medical School and director of the Precision Vaccines Program (PVP) at Boston Children’s Hospital, and David Dowling, PhD, instructor in pediatrics at Harvard Medical School and a member of the PVP, estimate that, worldwide, more than 24 COVID-19 vaccine candidates are in development. They explained that the vaccines generally fall into one of three categories:

• RNA-based vaccines. The first COVID-19 vaccines in development have used severe acute respiratory syndrome-2 (SARS-CoV-2) RNA. “This approach is innovative and attractive, but even if proven effective it may be difficult to create hundreds of millions of doses, and each dose may be relatively expensive as it may require a fair amount of RNA,” Dr. Dowling says. “While there is less experience with human testing for this approach, it is possible that adjuvants may help enhance the immune response when such vaccines are administered to older populations and may reduce the amount of RNA needed in each vaccine.”
• DNA-based technology. Like RNA-based vaccines, this method uses the genetic material of the virus to produce a vaccine. “You can make more vaccine doses with DNA than with RNA, but it is unclear whether the production could be rapidly scaled to meet the massive international demand,” notes Dr. Dowling. “And, to our knowledge, these nucleic acid vaccines have not yet been tested in elderly patients either.”
• Building on earlier coronavirus vaccines. The PVP is using this approach—learning from earlier vaccines from prior coronavirus outbreaks and making them more effective. “If you add an adjuvant chosen specifically for optimal activity in an older population, not only does it work better in that group, but it may dramatically reduce the cost per vaccine dose by reducing the amount of antigen required,” Dr. Dowling says.

Specifically, the PVP is trying to develop a vaccine targeted toward older populations, which are at greatest risk of developing COVID-19, caused by SARS-CoV-2.

“Elderly individuals have a different immune system than healthy middle-aged adults and often do not respond as robustly to immunization, so a one-size vaccine does not fit all,” Dr. Levy points out.

The current antigen used for vaccine development is the coronavirus spike protein, which PVP is attempting to combine with adjuvants to boost the recipient’s immune response.

“Overall, we are hoping that a precision adjuvant approach will assist the various ongoing vaccine efforts across the globe,” Dr. Levy adds. “Adjuvants can be crucial for getting a stronger, longer-lasting, broader immune response, especially among those with weakened immunity, like the elderly.”

While there are known vaccine adjuvants, the team will test new adjuvants it has discovered in the PVP’s National Institutes of Health–funded Adjuvant Discovery Program.

“These adjuvants were discovered by screening against human cells,” says Dr. Levy. “This species-specific approach represents an example of precision vaccinology.”

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