A couple of weeks ago, the European Commission set a target of vaccinating 70% of the EU’s adults by the start of summer, meaning June 1. But since then, COVID-19 vaccine producers have announced multiple production setbacks—so how achievable is that goal now?

“We are absolutely working towards achieving those targets,” said commission spokesperson Stefan de Keersmaecker on Monday, adding that 500 million doses of the Pfizer/BioNTech and Moderna vaccines—the first to gain approval from the European Medicines Agency (EMA)—will have been delivered to the EU by the end of September.

As it happens, 500 million is around the number of doses that will be needed to vaccinate 70% of the EU’s roughly 365 million adults—assuming each vaccination requires two doses, as is the case with all the vaccines that have been approved thus far.

So far, little more than 12 million doses have been administered in the EU. And, of course, the end of September is four months after the commission’s self-imposed deadline for 70% adult vaccination.

However, recent days have provided several reasons for hoping that the target might still be achievable:

• AstraZeneca’s two-dose vaccine gained EMA approval Friday, clearing the way for (highly politicized) deliveries to begin. Around half as many doses (40 million) will be delivered to the EU this quarter as were originally promised, but AstraZeneca’s output will likely rise in Q2. Overall, it’s on the hook to deliver up to 400 million doses to the EU.
• Johnson & Johnson announced positive trial results Friday, while saying it would apply for emergency authorization in the U.S. this week. EMA approval would likely take a while longer, but J&J’s entry into the fray would be hugely welcome, not least because its vaccine requires just one shot rather than two. An EU official said in mid-January that J&J could start delivering vaccines to the EU in April. The bloc has ordered up to 400 million doses.
• Pfizer and BioNTech said Monday that they will deliver 75 million more doses to the EU in Q2 than originally planned; that’s effectively a doubling of planned deliveries for the quarter. Their production has been boosted by the upgrading of a key manufacturing plant in Belgium, plus approval being given for manufacturing at another plant in Marburg, central Germany. France’s Sanofi, whose own vaccine is not panning out so well, will also produce doses of the Pfizer/BioNTech vaccine. The EU should receive up to 600 million doses of this vaccine alone during 2021.
• Don’t rule out Russia’s Sputnik V and China’s Sinovac vaccines for European deployment, at least not yet. German Health Minister Jens Spahn said Monday that they would be worth considering if the EMA gives them the green light, and EU member state Hungary has already partly authorized Sputnik V, with the intention of buying 2 million doses.

Meanwhile, Bayer on Monday officially agreed to make CureVac’s vaccine, a pronouncement that sent CureVac shares up more than 10% on Monday. However, this will have no effect on the EU’s 70%-by-summer target. CureVac’s interim trial data is only expected later this quarter; if it then gains EMA approval, the company is targeting the start of its rollout in Q2—and it would then be around half a year before Bayer starts boosting CureVac’s existing plan to produce 300 million doses this year.

“If everything goes according to plan, the first product is planned to be available at the end of this year,” a Bayer spokesperson told Fortune Monday. In 2022, Bayer hopes to make 160 million doses of CureVac’s vaccine in Wuppertal, western Germany. The EU is supposed to receive 405 million CureVac doses in total.

The European Commission is not the only organization to be hopeful about this summer: The low-cost airline Ryanair said Monday that it hoped to see a strong recovery in passenger levels between July and September, as the EU’s vaccination program becomes effective at scale.

However, the emergence of faster-moving variants of the SARS-CoV-2 coronavirus could require a very high proportion of the adult population to be vaccinated, if some sort of herd immunity is to become effective. Seventy percent coverage would be a mammoth achievement, but it would probably be only a step toward what’s needed.