If I got the one-shot Johnson & Johnson vaccine, do I need a booster because of Delta?

COVID Variants Vaccines

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While some scientists are sharing their own personal decision to boost their J&J vaccine with an mRNA second dose, the US vaccine regulators have not endorsed this strategy. This can put clinicians and pharmacists in a tough spot if a patient requests it.

Meanwhile, many countries including Canada and others in Europe are using a “mix-and-match” approach, pairing a first Astrazeneca (AZ) dose (a similar adenovirus technology to J&J) with a second mRNA dose to increase flexibility due to concerns about vaccine-induced immune thrombotic thrombocytopenia (VITT) with the AZ vaccine.

In fact Canadian Prime Minister Justin Trudeau and German Chancellor Angela Merkel both opted for a first dose of Astrazeneca and second dose of Moderna.

❓What do we know?

Several facts have raised the question of whether a booster for J&J might be desirable in the face of the rising Delta variant.

➡️ In the original trials, J&J’s shot was less effective than the mRNA vaccines at preventing symptomatic infection (66% vs 95% efficacy), though it was highly effective at preventing hospitalization (93% after 14 days & 100% after 28 days).

➡️ Data from the U.K. show reduced protection from one dose of AZ or mRNA vaccines against the Delta variant, while protection from two doses remains high. The drop in one dose protection was larger for the AZ vaccine.

➡️ Several new studies have shown that boosting adenovirus-based vaccine like AZ & J&J with an mRNA version results in a strong immune response and may even have immune benefits compared to two doses of the same vaccine.

❓What don’t we know?

➡️ While J&J and Astrazeneca have similar adenovirus technologies and dose (~5×1010 viral particles per 0.5ml dose), we don’t know whether one dose of J&J behaves more like a one or two dose AZ in the face of the Delta variant. This is because J&J has not been used in the UK where much of our real-world Delta data is coming from.

One potential difference is that the Astrazeneca vaccine is based on the “wild type” spike protein sequence while J&J and the mRNA vaccines use a slight modification to the sequence meant to stabilize the spike protein in the “prefusion” form (see link to previous post below). Again, how important this difference is for efficacy in the real world or in the face of variants is not known.
The only data we currently have on Delta and J&J come from small lab-based studies, which have reached different conclusions. These neutralization studies are also hard to extrapolate to real world protection.

A study of blood samples of people who had received one dose of J&J conducted by the company found only a small reduction in neutralizing antibody activity for the Delta variant, while a similar study by researchers at NYU found a significant reduction in neutralizing ability against Delta, especially compared to the mRNA vaccines.

Another Janssen (J&J) led study found durable immunity after 8 months in blood samples of people given the one-shot J&J, including against variants. Some immune responses even improved over time, suggesting the J&J vaccine may be particularly good at developing strong memory responses in the immune system. There is broader evidence that adenovirus vector vaccines such as Astrazeneca and J&J may elicit better T-cell responses than the mRNA vaccines.

Taken together, we admit the picture is far from clear in either direction. Our interpretation is that J&J is still quite good at protecting you from severe disease and death, which is the highest vaccine priority. Whether it protects as well against mild or asymptomatic infection is less clear and a more urgent concern with rising Delta cases.

We wish officials in the US would tackle this question more directly and give clear guidance (including acknowledging the full debate beyond the current official line that there is no evidence a booster is needed).

The US has begun trials testing explicitly boosting J&J with other vaccines, but we know that waiting for those results is not a satisfying answer to the millions of Americans who received J&J and are now watching cases rise again.

There are additional considerations of supply constraints globally that could argue against extra doses for those already protected from severe disease by J&J. But in the US the sad reality is that there are many mRNA doses expiring in the next month—so at the individual level this is less of a concern.


The one-dose Johnson and Johnson vaccine provides excellent protection against severe disease.

If you received J&J and are immunosuppressed or concerned about the transmission risk to others you live or work with, we encourage a discussion with your clinician about boosting options.

We know this is a frustrating topic, so we’ll promise to stay on top of the new data as it comes out!

Those Nerdy Girls

Further Reading:

“Americans are ‘mixing and matching’ Covid vaccines over concerns about the delta variant”

“J&J vaccine recipients Seek mRNA booster without CDC backing”

“You had the Johnson & Johnson coronavirus vaccine. Should you try to get a booster dose of Pfizer or Moderna?”

“Johnson & Johnson Vaccine Protects Against Delta Variant, Company Reports”

“J.&J. Vaccine May Be Less Effective Against Delta, Study Suggests”

New data on effectiveness of “mix and match”

Janssen/ J&J study on Delta neutralization

NYU Study on J&J & Delta neutralization

Durability of immunity over 8 months J&J

T-cell ‘training grounds’ behind robust immune system response seen in adenovirus vaccines

US doses expiring

Previous DP post on pre-fusion and post-fusion spike protein for vaccines

Link to Original FB Post