Novavax released their initial results on Wednesday as a press release. These results have not yet been submitted for publication or subjected to peer review. 

In a U.K. trial including 15,000 participants, the vaccine demonstrated an overall efficacy of 89.3%. At first glance, that number appears a bit lower than the 94% number from Moderna and the 95% value given by Pfizer. However, in the Novavax trial, about half of those U.K. participants were infected by the fast-spreading B.1.1.7 variant.

By sequencing the virus strains of infected patients, Novavax gave an estimated efficacy of 95.6% against the original COVID-19 strain and 85.6% against the B.1.1.7 U.K. variant.

Novavax also reported results from a phase 2B trial in South Africa, and there the results are more complicated. Overall efficacy in South Africa was just 49.4%—a sharp drop from the numbers seen in the U.K. However, about 6% of the South African sample population was HIV-positive and about a third showed SARS-CoV-2 antibodies at the outset of the test, indicating they likely had a COVID-19 infection at some previous point. Preliminary data shows that 92.6% of those infected in the South Africa group had the new, rapidly spreading B.1.351 variant. How all these factors play into the results isn’t clear. However, omitting the HIV positive group, the vaccine was 60% effective in South Africa. This suggests that on a variant-by-variant basis, the vaccine is 35% less effective against the B.1.351 variant than it is against the original virus (including the European variant that developed soon after the virus spread out of Wuhan).

In addition to the U.K. and South African trials, Novavax has phase 3 trials in both the U.S. and South America. However, these trials began recruiting significantly later than those reported on Thursday and should not be expected to return results before the end of February.

Johnson & Johnson’s data also represents interim results released by the company, not peer-reviewed data. This data comes from a large-scale, multicountry ENSEMBLE trial that was treated as a single trial when compiling cases against the endpoints (i.e., the targeted number of infections that triggers the end of a trial), then data was broken again by region. Overall, 44% of Johnson & Johnson’s volunteers were in the United States, 41% were in Central and South America, and 15% were in South Africa.

Johnson & Johnson reports the efficacy of their vaccine as 72% effective in the United States, 66% in Latin America, and 57% in South Africa.

However, there are some big caution flags to go with this data. The primary one is that Johnson & Johnson is reporting something distinctly different than every other vaccine manufacturer. They’re giving an efficacy number representing “protection against moderate to severe COVID-19 infection.” Meaning that they’re not including mild or asymptomatic infections in this value. This is a valid way of representing the data, but it is different from what other vaccine manufacturers have reported.

Previous results from Moderna and AstraZeneca have indicated that their vaccines are also effective in preventing spread of COVID-19. By excluding mild or asymptomatic cases, Johnson & Johnson seems to be ruling out the idea that their vaccine can effectively prevent contagion.

The Johnson & Johnson numbers also represent a “time slice” of the vaccine’s efficacy 29 days after injection. It takes some time for any vaccine to become effective, but by eliminating infections that happened in the first month after the vaccine was administered, Johnson & Johnson has definitely removed some cases that were included in the accounting of other manufacturers. When the full dataset from these trials is released, expect published numbers to look significantly different.

As with Novavax, the differing numbers for efficacy in different regions is mostly attributable to the variants involved. In the South Africa results, 95% of those infected caught the B.1.351 variant. It’s not clear if the Latin America results include patients infected with the Brazil P.1 lineage, but that might explain the lower numbers in that region as the P.1 variant has mutations in common with the B.1.351 variant.

Ignoring milder cases may make it seem as if Johnson & Johnson is inflating the efficacy of their vaccine. Still, turning COVID-19 into a mild, cold-like illness is no mean feat, and there is also some very good news in the data. 

One of the reasons that Johnson & Johnson’s vaccine has been so closely watched is that it requires only a single dose. What the data from these preliminary results reveals is that this single shot seems to provide more and more protection as time goes on. In fact, after 49 days, the number of vaccine patients infected was 0. Across all regions. That’s not a promise of perfect efficacy for people willing to keep their masks on for a couple of more months—after all, a majority of those involved in the study were not even vaccinated for 49 days when this data was calculated—but there are strong signs that the vaccine gets better over time, even against the most elusive variants.

Novavax is already seeking approval for their vaccine in the U.K. However, don’t expect the company to appeal to the FDA for an emergency use authorization until the data is back from the U.S. and South America trials. The U.S. has already reserved 100 million doses of the Novavax vaccine, but don’t expect them to be available before April or May.

Johnson & Johnson now is about where Moderna or Pfizer were at the beginning of November. Expect another week or two for the trial to hit its final endpoints. Then at least a couple of weeks for Johnson & Johnson to prepare this data for submission to the FDA. As indicated above, the public reporting of their data differs from that of other manufacturers, and it’s unclear how they will organize their information for the FDA or how the expert panel will move forward. A best case scenario might see this vaccine becoming available in early March.

Vaccine Efficacy
VaccineU.S.U.K.S. africaL. America
Novavax*89%49%
J & J**72%57%66%

* U.S. and Latin America trials still underway

** Reports only prevention of moderate and severe cases of COVID-19