Two new studies have shown the real-world effectiveness of the Pfizer-BioNTech vaccine rollout against two deadly Covid variants, B.1.1.7 and B.1.351. The news is decidedly positive, especially when considered alongside data from a third study, released today, on the effectiveness of a Moderna booster shot against B.1.351 and the P.1 variant. But despite the positive momentum, it remains far too soon to call the game in our favor nor trust too much in vaccines alone to end the virus’ spread.
The first set of data comes out of Qatar, which launched its mass immunization campaign with the Pfizer-BioNTech vaccine in late December just as its second major wave of infection was beginning to rise. By mid-March, at least half of all cases in Qatar were caused by the B.1.351 variant and 44.5% were caused by B.1.1.7; around that point roughly 385,000 Qataris had received at least one vaccine dose and roughly 265,000 had received both doses.
The study found that, despite the prevalence of the variants, the vaccine was still highly effective at preventing infection. Two weeks after the second dose, the Pfizer vaccine’s effectiveness against infection from the B.1.1.7 variant ranged from 87-89.5%. Against the B.1.351 variant it ranged from 72.1-75%. More promising still, the vaccine was 97.4% effective at preventing severe or fatal Covid-19 from any SARS-CoV-2 virus, including both variants.
This is excellent news, but it bears noting that for the B.1.351 South African variant, the vaccine was still 20% less effective at preventing infection than in the initial clinical trial. Also worth noting is the difference in effectiveness after one dose compared to two. There were 6689 breakthrough infections and 5 deaths reported among those who had received only one dose of the vaccine and only 1616 breakthrough infections and 2 deaths in those who received the full two.
A second study — using national surveillance data from Israel during the first four months of its campaign which began just as the country reached the peak of its second big wave — echoed the positive findings from Qatar. The B.1.1.7 variant is by far the dominant strain across Israel, accounting for nearly 95% of all cases. In this study, seven days or more after the second dose, the Pfizer vaccine proved 95.3% effective at preventing infection and 97.5% effective at preventing severe or critical Covid-19.
This study also went a step further, analyzing vaccine uptake and its impact on the scope of the nationwide epidemic. It notes that as the percentage of vaccinated people in each age cohort grew, the number of coronavirus infections in that age group fell and that even in the face of the country’s phased reopening, reductions in new infections continued. Taken together, the authors note that this suggests that high vaccine coverage might prove to be a sustainable path towards resuming normal activities.
Again, excellent news but also not without caveat. The study contains only seven weeks of follow up data following the second dose of the vaccine — the longest follow up data we have to date but still not long enough to determine whether protection against the variants lasts as long as protection lasted against the non-variant strain dominant in the clinical trials. What both the Israeli and Qatari studies do show us definitively is that high titers correlate to broad protection, which will be important for measuring new vaccines and the effectiveness of booster shots.
And that is where the third study comes in, a Phase 2 study from Moderna on the effectiveness of its booster shot against variant strains of the virus. While the full data has yet to be released, Moderna’s press release shows a single dose booster shot given to someone who has already received both doses of the vaccine raises the body’s neutralizing antibody titers against both the B.1.351 variant and the P.1 variant which was first identified in Brazil, the only two variants seemingly tested in the study.
Beyond that important finding, Moderna also tested a strain-matched booster shot and compared its effectiveness against the original booster. The strain-matched shot was designed specifically to match the B.1.351 variant — that boost raised even higher neutralizing antibody titers against the B.1.351 variant than the original. This too is excellent and welcome news.
Despite the positive notes that run throughout all these findings, it’s important to note that none of these studies give us any indication of how well our vaccines and potential boosters will perform against other variants, both the ones we know of today and the ones — perhaps even deadlier or more transmissible — that may emerge tomorrow.
In addition, and perhaps more importantly, if people don’t agree to vaccination the vaccines won’t do any of us any good, no matter how effective they may be. In many countries around the world, including here in the United States, widespread vaccine acceptance is not a given. Because of this, any discussion of reopening or resuming pre-pandemic activities must take other public health precautions like mask-wearing and social distancing into careful consideration. We haven’t won the game just yet, but as these studies show, the opposing team can definitely be beaten.