Experts Torn Over Half-Dosing Moderna, Pfizer COVID-19 Vaccines

January 21, 2021 - Recently, experts have considered delaying, skipping, or half-dosing Moderna and Pfizer-BioNTech’s COVID-19 vaccines to reach more people in need and create a more wide-spread immunity. 

Currently, the dosing interval for Moderna is 28 days, while the interval for the Pfizer dose is 21 days.

According to FDA, the decision to half-dose the vaccines would be premature and not rooted solidly in available evidence. Altering the dosing schedule could be detrimental in the long-run. 

In the following article, PharmaNewsIntelligence breaks down the pros and cons of half-dosing COVID-19 vaccines and the effect these changes could evoke. 

Pros of Half-Dosing COVID-19 Vaccine Injections

The first dose of a vaccine is called the priming dose and the second dose is called the booster. Generally, vaccine doses are administered at least four weeks apart to elicit the highest immunity. 

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While many experts believe the interval between COVID-19 vaccine doses is crucial to obtain optimal antibody responses, others believe there is enough data to prove the benefits of half-dosing. 

According to Pfizer data released in December, the Pfizer-BioNTech mRNA-based COVID-19 vaccine candidate, BNT162b2, was nearly 52 percent effective after the first dose in over 36,000 participants in a Phase 3 clinical trial.

And data from Moderna presented to the FDA showed that the company’s COVID-19 vaccine, mRNA-1273, can provide 80.2 percent protection after one dose.

Some experts, including Chris Gill, infectious disease specialist at Boston University, have called on governments to give out single COVID-19 vaccine doses after the preliminary research from both companies. Gill suggested that one dose may provide notable protection. 

“We could save a lot of lives. We can give two doses to people now, but in the interim a bunch of people who could have gotten the vaccine are going to die. Is this not an example of where, yet again, the perfect is the enemy of the good?”, Gill said in a December press release.

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Although most scientists follow vaccine dosing schedules that are released by pharmaceutical companies or agencies, the COVID-19 crisis has called for more drastic measures.

Robert Wachter, chair of the department of medicine at the University of California, San Francisco, stated in a press release that he generally does not support reducing vaccine doses. But since COVID-19 cases have surged over the past few months, a change of course may be needed.

“It felt like it may be time where we have to be a little more creative and accept the possibility that we may need to do something with a little less evidence,” Wachter said. 

Scott Gottlieb, a former FDA commissioner and a member of Pfizer’s board of directors, called the move to half-dose “a prudent move that will help expand COVID vaccine access to more high-risk patients at a time when the epidemic is worsening,” in a Twitter statement at the beginning of January.  

As countries work to stop the spread of the coronavirus, each will have to weigh the question of how quickly they can vaccinate the population. Most recently, the UK has discovered a new strain of COVID-19.  

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Tony Blair, former prime minister of the UK, stressed in an opinion piece that the British government should use all the available doses in January as first doses and not keep half back for second doses. Even the first dose will provide “substantial immunity,” he explained. 

Additionally, analysis from experts and researchers in Canada found that holding back vaccine doses would essentially mean that more individuals would get infected with the coronavirus.

Because currently there is no shortfall in manufacturing of doses expected, the move to keep them in reserve would be disadvantageous.   

Cons of Half-Dosing COVID-19 Vaccines

Generally, two doses of any vaccine are given in order to obtain high antibody titers. An individual’s immune system is able to respond more effectively to the second dosage of a vaccine rather than to the first dose. 

At the beginning of January, president-elect Joe Biden’s team suggested that when the administration takes office, it will release the available doses of COVID-19 vaccines. Biden said the timeline was 100 million shots in the first 100 days of his presidency.

Introducing drastic vaccine schedule changes may create more problems than it solves.

There is little to no evidence to indicate long-term effects of discarding the booster shot for a COVID-19 vaccine. Most experts agree that a single dose would likely be less effective and it could be just months before the immunity fades. 

For example, Phase 3 clinical trials for both Moderna and Pfizer-BioNTech’s COVID-19 vaccines showed that individuals who did not receive two doses at either interval week were only followed by experts for a short period-of-time.

Therefore, FDA stated that neither the agency, nor scientists, can conclude anything about the duration of protection after a single-dose of a vaccine from the single-dose percentages reported by each company. 

Additionally, deviating from the science behind both mRNA-based COVID-19 may also cause more harm than good. 

Policymakers adhere to the sciences in every step of the process when developing top COVID-19 vaccines. If there was a sudden change in course and states and countries began adopting policies that stray from clinical trials, patients and the public would feel that they were misled. 

According to Ashish K. Jha, MD, MPH, dean of the Brown University School of Public Health, changing the dosing levels would further “fuel vaccine hesitancy and erode trust in public health.” 

There is a crucial ethical consideration when considering half-dosing, too. Individuals who chose to get the first dose have the expectation that they will receive the second dose in a certain time frame. 

Ultimately, it is unethical to withhold the second shot from these individuals, some have said. Experts believe that Biden’s administration must guarantee high production so there will be enough second doses for all first doses given.

“In vaccines we have a saying: A dose delayed is often a dose never received,” William Schaffner, MD, a Vanderbilt University professor of preventive medicine in the department of health policy and the division of infectious diseases, said in a press release. 

“We have to be very attentive in getting people back. The more you stretch it out between doses, the more you’ll find people drop off. That certainly is something we do not want,” Schaffner continued. 

Most notably, Biden’s plan to allocate single-doses to individuals goes against FDA’s warning to health officials to follow the authorized dosing schedules for COVID-19 vaccines as the first round of recipients are now becoming eligible to receive their second doses.

“Without appropriate data supporting such changes in vaccine administration, we run a significant risk of placing public health at risk, undermining the historic vaccination efforts to protect the population from COVID-19,” FDA stated in the announcement. 

Therefore, any changes to the dosing schedule for any COVID-19 vaccine is premature, not supported by scientific evidence, and could be counterproductive to public health.