The covid-19 pandemic was rife with uncertainties and false moves, and the inability to understand the complexities and communicate clearly has set us back for every scientific advance that has taken us forward. We got the welcome news this month that mRNA vaccines are safe and protective against symptomatic covid-19.
To the U.S. as part of their applications Both Pfizer/BioNTech and Moderna submitted a convincing finding to the FDA for emergency approval: that the vaccines offer some protection as soon as 14 days after the first vaccination. The principle of using these strategies to increase the number of vaccinated individuals has rapidly gained support.
In a time of crisis, with little data, officials could be justified in making such a decision to make the most of limited supplies of vaccines to protect as many people as possible. The Joint Committee on Vaccination and Immunization in the United Kingdom has expanded the time period for a second dose of Pfizer/mRNA BioNTech’s vaccine from three weeks to up to 12 weeks, the interval used in clinical trials that demonstrated 95% efficacy in protecting against covid-19. (A second dose of AstraZeneca vaccine, the other vaccine approved in the United Kingdom, can also be administered in practice backed by clinical trial evidence up to 12 weeks after the first one.) In the United States, Ron DeSantis, Florida’s governor, is stated to have indicated that one dose may be adequate.
In Ontario, Rick Hillier, who is responsible for the delivery of vaccines in the most populous province in Canada, has asked regulators to consider whether a single dose of Moderna vaccine can be given.
And Dr. Moncef Slaoui, the technical advisor for Operation Warp Speed, the U.S. vaccination program, has recommended that the dose of Moderna vaccine be cut by half.
In these and other situations, the idea is: if we could vaccinate more people, more lives would be saved and the pandemic would end sooner, wouldn’t it? Maybe not.
Vaccine efficacy decreases to about 50 percent after a single vaccination for both mRNA vaccines, according to the study results. Since this calculation covers the 14 days immediately after the first vaccine (before the initiation of the full immune response), it indicates that much less protection would be offered by a single vaccination. Even excluding the first 14 days, after which efficacy is expected to reach 90 percent, the confidence intervals indicate that this safety could differ by almost 30 percent – or what researchers estimate to be the range of true efficacy. This is also in contrast with evidence from previous mRNA vaccine studies against both Sars-CoV-2 (the cause of Covid-19) and Mers-CoV, its relative.
Studies of Sars-CoV-2 infection in monkeys indicate that for a single mRNA vaccine to be protective, the dose must be higher. Phase 1 clinical trials evaluating healthy volunteers’ tolerability and immune responses to different doses have shown that higher doses have been associated with more serious side effects.
Whether a single-shot vaccine could be both preventive and healthy is doubtful. Science also does not support the claim that the second (booster) shot of an mRNA vaccine could be postponed.
We do not yet have knowledge on the longevity of the immune system, i.e., how long the protective immunity lasts, because of the rapid study process. Some vaccines may not need booster shots to do so, but these usually use vaccine platforms containing harmless virus replication that are either attenuated (called live attenuated vaccines) or used as vehicles to transport parts of the target virus’ protein (viral vectored vaccines). Johnson & Johnson’s vaccine is a viral vectored vaccine and is being tested as a single vaccine, which is scheduled to complete Phase 3 clinical trials in January. This type of vaccine will activate the immune system more strongly than mRNA vaccines over a longer period of time (although this is not always the case, as with the Oxford/AstraZeneca vaccine, which involves two doses of a viral vectorized vaccine). In essence, mRNA is a rapidly degradable set of instructions for cells to generate the Sars-CoV-2 spike protein.