The US Food and Drug Authority (FDA) recommended a temporary pause of the use of Johnson & Johnson’s single-shot Covid-19 vaccine on 13 April following reports of six blood clots – one of them fatal – developing among women who received the jab. Nearly seven million Americans have been vaccinated with the Johnson & Johnson jab, according to figures from the US Centres for Disease Control and Prevention.
As with AstraZeneca’s vaccine, which many national regulators have now restricted for use in older patients only, Johnson & Johnson’s jab is based on viral vector technology, rather than the messenger RNA used in the Pfizer and Moderna vaccines. Viral vector vaccines use a modified version of a different virus – in the case of both J&J and AZ, an adenovirus – to instruct the immune system how to construct an antibody response to coronavirus infection. Although the cause of the very rare blood clots apparently linked to J&J and AZ remains unknown, some scientists have speculated that it may be related to an unusual immune system reaction to the vector.
The news that the use of the J&J vaccine is being paused, and that it could be restricted, may not prove disastrous for the US vaccine programme. The J&J vaccine represents a tiny proportion of the total 190 million vaccine doses so far administered in the US, which has mainly used Pfizer and Moderna.
Yet for the EU, the outlook may be more mixed. The bloc had been pinning some of its hopes of vaccinating 70 per cent of its adult population by the end of the summer on J&J, and received its first doses of the vaccine this week. Peter Liese, a leading German MEP, had said that the new jab would allow the pace of vaccinations in Germany and Europe to “massively accelerate”.
Of the three double-dose vaccines so far approved by the EU, the EU Commission is expecting 200 million deliveries from Pfizer, 70 million from AZ and 35 million from Moderna by June, enough to fully inoculate more than 150 million Europeans. Brussels is expecting delivery of 55 million J&J doses over the same period, enough to fully vaccinate 55 million people. On 14 April, Pfizer announced that delivery of an addition 50 million doses would be brought forward to the second quarter, for a total of 250 million doses.
The European Medicines Agency, which approved the use of J&J in March, has already begun reviewing reports of clotting in Americans who have received the jab. A recommendation by the EMA to restrict the use of J&J would likely prove a further setback for Europe in its troubled vaccination programme.
Even if the EMA continues to recommend J&J for most or all age groups, some national regulators could still choose to restrict its use regardless. This has already happened in the case of the AZ vaccine, which has been banned for younger people in several European countries despite the EMA ruling in its favour.
There is also the possibility that some people might now be more hesitant to take the J&J jab if offered, preferring to wait for an alternative vaccine.
Yet the evidence from AZ is that while take-up has suffered following the review and restrictions, doses mostly continue to be used, although at lower rates than other vaccines. Based on this precedent, the latest news may prove a hitch, but not a catastrophe.
[See also: How the EU’s naivety led to its vaccine debacle]