After an estimated 98 million doses of Covid-19 vaccines have been administered in 62 countries, two more vaccine candidates aim to join the fight. Novavax and Johnson & Johnson (J&J) have released preliminary efficacy data from their large scale phase 3 trials. These two vaccines are particularly interesting in that they both keep in mind and track efficacy against emerging SARS-CoV-2 variants from the United Kingdom (B.1.1.7) and South Africa (B.1.351). Their efficacy estimates present critical insights for the potential immune-resistance of these variants.

The vaccines, first and foremost, were effective in protecting against the most widely circulating strains. From their phase 3 UK trial, the two-dose Novavax vaccine recorded a 95.6% efficacy in preventing Covid-19 symptoms in cases with the original UK virus. For J&J, their vaccine efficacy was lower for the most widely circulating strains but was still moderately effective at around 70%. We need as many efficacious vaccines available as possible; adding two more is a positive development.

J&J’s one-dose vaccine landing around 70% may speak to the single dose or merely to testing on a different population at a different time with different circulating strains in the test population. It is challenging to compare trials done with so many different variables. J&J’s vaccine may have performed better a few months ago on a different test population, but we will never know.

These vaccines also present distinct advantages over previous vaccines like Moderna, Pfizer, and Oxford. They both do not require cold-chain storage as the others do. Supercooling storage containers are inaccessible in many parts of the world, and not requiring them speaks to the stability of these vaccines. J&J also only features one-dose, which cuts logistical costs in half and makes vaccination much more accessible to low-income countries.

Speaking to the new variants tested in these new trials, B.1.1.7 and B.1.351 were just beginning to gain notoriety when Moderna, Pfizer, and others announced their 90+% efficacy rates late last year. Novavax and J&J were able to conduct studies in the UK and South Africa with the new variants in mind; they were explicitly tested to determine variant efficacy.

Because of this, both vaccines had variable efficacy rates in different countries. While the circulating variants certainly played a role in variable efficacy between the UK, South Africa, the US, and Mexico between the two trials, there is also a chance that varying demographics played a role in the differing efficacy rates. 

This point of differing populations is highlighted by both vaccines’ lower efficacy against B.1.1.7 and B.1.351. In the Novavax UK trial, 32 of the 62 participants in the efficacy analysis were identified by genome sequence with the B.1.1.7 strain. Among those infected with B.1.1.7, the vaccine was 85.6% efficacious in preventing symptoms. For both Novavax and J&J, efficacy against B.1.351 dropped below 60% in their South African trials.

These B.1.351 results carry a bit of an asterisk. In the Novavax trial, several patients were previously infected with SARS-CoV-2 strains from earlier in the pandemic, along with many HIV-positive participants. It’s tough to determine a vaccine’s exact efficacy when there are previously infected participants with potential antibodies, as well as immuno-compromised participants. Novavax claims effectiveness of 49.6% for all subjects and 60% for HIV-negative subjects. This vaccine’s real efficacy against variant strains is unknown because they tested a mixture of the original and new variant.

The J&J press release falls into a similar trap, claiming a 57% efficacy in their South Africa trial without accounting for those with the previous infection.

Ultimately, the data from Novavax and J&J indicates a moderate to strong efficacy against the widely circulating strains of SARS-CoV-2, as well as B.1.1.7. The less encouraging news is that B.1.351 seems to be able to reinfect, according to the Novavax trial and accompanying studies in recent weeks. B.1.351 is also at least moderately immune-resistant compared to B.1.1.7 and other significant strains of SARS-CoV-2, as demonstrated by both trials. Our best hope is to vaccinate as many as possible, implement stringent public health measures, and hope immune-resistant virus strains cannot wreak the havoc we know is possible.