The suspended rollout of AstraZeneca Plc’s Covid-19 vaccine in some European Union countries over concerns about possible side effects could delay a goal of immunizing three-quarters of their populations by as much as a month.

Limiting the use of the AstraZeneca shot as a precautionary measure could push back efforts to hit that threshold by at least a couple of weeks and potentially longer -- to September instead of August -- according to London-based research firm Airfinity Ltd.

While the European Union is relying heavily on the AstraZeneca-University of Oxford inoculation, it has a number of weapons at its disposal in the race to escape the pandemic. Those include vaccines from Pfizer Inc. and its partner BioNTech SE, as well as Moderna Inc. The bloc last week cleared Johnson & Johnson’s shot, too, though it’s not yet available for use.

The bloc will need all of those supplies as it seeks to make up for a sluggish start to its immunization campaign. Beginning in the second quarter of the year, other shots are expected to take on more of the burden from the AstraZeneca and Pfizer vaccines, which have accounted for most of the injections given so far. Now the suspensions, along with continued production delays for the AstraZeneca vaccine, threaten to slow the pace of immunizations further.

The Netherlands joined about a dozen places, including northern Italy and Ireland, in deciding to suspend AstraZeneca’s shot amid reports of serious blood clotting. But regulators from Europe to Asia said there was no indication of any direct link with the vaccine.

AstraZeneca said more than 17 million doses had been administered in Europe and the UK, with no evidence that the shot increased the risk of blood clots. As of March 8, there had been 15 reports of clots in the legs, called deep vein thrombosis, and 22 cases where they reached the lungs, known as pulmonary embolism. The company said it is continually monitoring safety.

Denmark’s medicines regulator said Monday that a 60-year-old woman who died after receiving the AstraZeneca vaccine suffered from an “unusual” combination of symptoms that are now being thoroughly investigated by the European Medicines Agency and other authorities.

Supply woes and questions about the initial trials that extend to the shot’s efficacy against novel variants have hit the AstraZeneca vaccine. Even as some countries suspend its use, others like the US are moving to protect their own stockpiles, blocking efforts to redistribute the shot’s supply to places with urgent needs.

There are a number of factors that could affect the pace of the immunization campaign in Europe and elsewhere over the coming months. But if doubts grow and people are slow to get vaccinated across the continent, the European timelines could be pushed back even further, according to Airfinity.

The EMA is scheduled to evaluate data on the AstraZeneca shot on Thursday, Marco Cavaleri, chair of the regulator’s vaccine evaluation team, told Italy’s Radio24.

The regulator sees “no reason to stop using” the injection, he said. “Still, we understand the position of member states which, as a precautionary measure, prefer to wait until we complete our investigations.” (Bloomberg)