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Scientists caution against comparing immune responses shown in early-stage trials, and say there might be more than one path to an effective vaccine. When it rains, it pours. In the past few days, scientists working at feverish pace to develop vaccines against the coronavirus have released a flood of data from their first human trials. The results come from phase I and II trials of four promising vaccine candidates, and detail how people respond to the jabs. Because the trials were focused on safety and dosing, the data cannot say whether the vaccines will prevent disease or infection — large-scale efficacy trials are needed for this. But they suggest that the candidate vaccines are broadly safe, and offer the first hints that vaccines can summon immune responses similar to those of people who have been infected with the virus. Crucially, researchers say the data look good enough to merit testing the vaccines in efficacy trials, in which volunteers receive a vaccine or placebo and rates of COVID-19 disease are compared between groups.
“I’m really happy that there are quite diverse vaccine strategies going beyond phase I trials,” says Shane Crotty, a vaccine immunologist at the La Jolla Institute for Immunology in California. But scientists caution against over-interpreting the results, and say the data shouldn’t be used to compare the vaccines directly. Eventually, such comparisons will be key to identifying how the vaccines work, or why they fail. The information will also be used to prioritize other vaccines at early stages of development and to design new ones. But none of this is possible yet, because researchers don’t know the precise nature of the immune responses that protect against COVID-19 — and there are likely to be multiple ways to fend off infection. Furthermore, measurements of immune markers made in one lab are difficult to compare with those performed by another team, say scientists. “The data are so early and so preliminary; one thing to avoid is saying one is better at this stage, because we just don’t know,” says Rafi Ahmed, an immunologist at Emory University in Atlanta, Georgia...
