Biopharma companies are burning the midnight oil developing vaccines against the novel coronavirus.
Thirty-six candidates are in clinical evaluation and 146 are in preclinical testing, according to the World Health Organization's latest draft landscape document.
A vaccine might not work, SVB Leerink analyst Geoffrey Porges said in a new note, although he added that he's not predicting failure, but tempering expectations.
The analyst named seven reasons for the cautious stance:
The Immunity May Not Be Strong Enough: Most vaccine candidates for which Phase 1 or 2 results are published have established immune response, but have not produced strong protection against COVID-19, Porges said.
The Immunity May Not Be Broad Enough: Most vaccine candidates encode or deliver the surface spike protein of SARS-CoV-2 and are capable of generating an immune response against this specific target, the analyst said.
This means the breadth of the immune response is narrower than the actual infection, he said.
"It is still unclear whether humoral or cellular responses to other antigens, such as for example the N protein or M or ORF proteins, may contribute to protective immunity."
Longevity Of Immunity In Doubt: The ongoing Phase 3 studies of coronavirus vaccine candidates demonstrate short-term efficacy, given the trial design and endpoint selection, Porges said.
Follow-up of greater than six months is needed for a clearer picture, the analyst said.
Vaccine May Not Be Safe Enough: Coronavirus vaccines are for use in broad populations across different age and risk groups, and even serious adverse events with very low frequency can lead to widespread adverse events and even vaccine withdrawal, Porges said.
The reactogenicity — or adverse reactions — that arose soon after vaccination and were seen in Phase 1 coronavirus vaccine candidate data are substantially higher than current commercial vaccines, the analyst said.
Clinical Study Execution Challenges: The complicated operational demands of hastily designed, large, multi-country trials pose execution challenges, Porges said.
Logistics Challenges: The stringent temperature requirement for mRNA vaccines storage could significantly limit vaccine distribution, storage and administration, the analyst said, citing AICP.
Most commercial classes of vaccines have a relatively long shelf life under less stringent conditions, according to SVB Leerink.
Vaccine Avoidance By Consumers: Herd immunity, when the majority of a population is immune to an infectious disease, could impact the wide adoption of vaccination, Porges said.
"Herd immunity is achieved when a level of population immunity decreases or stops the disease spreading after all preventative measures have been relaxed," the analyst said.
A recent Science article suggests 43% immunity might be sufficient for COVID-19 after accounting for age cohorts and social activity, according to SVB Leerink.
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