Anyone who opted to receive the “one and done” Janssen coronavirus vaccine may potentially have to receive a second jab if they hope to be protected against the highly contagious Delta variant, new research suggests.

NYU study finds Janssen is less effective against Delta variant

Over the past few weeks, a number of people across the Netherlands have chosen to book appointments for the Janssen vaccine, as only one jab would provide them with sufficient protection from the virus as well as a vaccination certificate in the CoronaCheck app. Instead of having to wait weeks for the second jab, after just one appointment these people would be able to go out to nightclubs, attend events, or travel internationally. 

But Janssen has proved significantly less effective against variants of COVID-19 than either the Pfizer / BioNTech or Moderna vaccines. And as the Delta variant continues to spread across Europe, new research conducted by the NYU Grossman School of Medicine has suggested that anyone who received the Janssen vaccine should have a second jab - preferably either Pfizer or Moderna. 

Mixed response from Dutch medical experts

The NYU study compared the blood of people who received either Pfizer or Moderna and people who received Janssen, and found that, due to the lower amount of neutralising antibodies three months after vaccination, anyone vaccinated with Janssen was less protected against the Delta variant.

Professor of vaccinology in Leiden, Ben van der Zijst, told Het Parool the results of the study were in line with other studies investigating the efficacy of Janssen. “After a jab with Janssen you are simply more susceptible to getting infected. This increases the chance of transmitting the virus,” Van der Zijst said. “That is why I think that a second shot after Janssen is inevitable in the long run.”

However, some medical experts here in the Netherlands have been critical of the study’s results, highlighting the fact that research conducted by Public Health England found that Janssen was 85 percent effective in preventing serious illness, hospitalisation, or death from the Delta variant. 

Possibility of a booster jab in the Netherlands

In the Netherlands, over 750.000 people have been vaccinated with Janssen. But head pharmacist at Erasmus MC in Rotterdam, Hugo van der Kuy, says Health Minister Hugo de Jonge shouldn’t rush into organising second jabs for those people: “In my opinion, the study is a storm in a teacup,” he told Het Parool.

The Ministry of Health has asked the Health Council of the Netherlands to provide advice in regards to offering everyone an additional shot - a so-called booster jab. This would apply to everyone who has been fully vaccinated, not just those who received Janssen. Pharmaceutical company Pfizer has also asked the European Medicines Agency (EMA) for approval for administering a third dose 12 months after the second jab.