The public is questioning the actual efficacy of the alternative regimen of the COVID-19 vaccine that reduces dose or delays the booster dose due to the vaccine shortage,

Relevant experts give conflicted opinions. Some argue the government should maximize the efficacy with the limited resource, whereas some claim medical evidence is integral before making a hasty decision.

▲Three conflicts: delaying second dose, switching vaccine type and reducing dose volume

The main considerations on the vaccine inoculation plan are spacing out the vaccine interval designed at the clinical phase, switching between vaccine types, and lessening the vaccine dose instead of delaying the interval.

All conflicts are caused by the shortage in the COVID-19 vaccine. The health authority means to distribute the limited vaccines as much as feasible.

Professor Kim Woo-joo at Korea University Hospital Department of Infectious Diseases said, “Delaying the second dose timing, although it has not been scientifically proven, would be cost-effective to immediately block off the COVID-19 transmission and to minimize the damage. But it does not have to be considered as South Korea’s situation is as not urgent as the situation in the U.K.”

▲Experts OK delaying second dose

Vaccine and infectious disease experts show open stance on the longer vaccine interval. As the second dose serves as a booster for the first dose, they claim taking the two doses is more important than the timing.

Professor Choi Yong-jun of Hallym University College of Medicine explained, “When it comes down to vaccine inoculation, a short interval can be problematic, but delaying it does not raise a concern. This is one of basic principles of vaccine inoculation.”

The booster dose activates the immunocytes and antigen memory inducing the antibody reaction after the first dose. The second dose is only needed as a single shot of vaccine cannot guarantee 100-percent immunogenicity. In other words, the longer interval does not drastically affect the efficacy of the vaccine.

▲On switching the vaccine types, ”Absolutely not”

Meanwhile, the experts are leaning towards an absolute negative stance on mixing the vaccine types. The U.K. authority considered inoculating Pfizer vaccine for the first dose and AstraZeneca vaccine for the second, but they had to withdraw the plan after the public criticism that there is not enough clinical evidence to ensure safety in the switch.

Director Kang Jin-han at the Catholic University of Korea Vaccine and Bio Research Center firmed noted “The vaccine type switching is definitely not advisable. There is no evidence and it is unethical.”

With a concerned voice, he added, “The clinical trial protocol on confirming the efficacy of a COVID-19 vaccine was conducted twice with the same vaccine type. Nobody knows what would happen when using two types of vaccines.”

▲Unsure of the low-dose inoculation

Then, how about inoculating a lower dose vaccine, instead of a full dose? The experts carefully say the efficacy should be verified first. Theoretically, the full-dose inoculation would be idealistic to confirm the efficacy, but strangely there was a case a vaccine performed better with lower dose.

During the Phase II/III trial on AstraZeneca’s vaccine candidate AZD1222, about 10,000 participants aged over 18 were inoculated twice with a month-long interval, and their prevention effect was checked after two weeks.

The result found 2,741 people who received one dose achieved 90 percent of the effect, whereas 8,895 people with the two full doses only reached 62 percent. The vaccine efficacy improved by 28 percent-point with the one dosing regimen.

Moderna disclosed research findings that half a dose of vaccine demonstrating similar effect with a full dose. Generally, lesser dose should show equivalent or inferior efficacy than the full dose, but AstraZeneca’s vaccine performed better with reduced dosing.

Korean Society of Infectious Diseases (KSID) official pointed out, “The appropriate evidence of a lower dosing performing better than higher dosing cannot be found. We need a large scale clinical trial for more credible source of evidence.”

▲The health authority’s decision based on vaccine supply "

The daily confirmed case count of COVID-19 in South Korea has dropped under 500. Taking account of the situation, the radical inoculation plan to switch the vaccine type or delaying the booster dose sound unrealistic at the moment.

The Ministry of Food and Drug Safety (MFDS) official stated, “Except for an alarming crisis in the pandemic control, vaccination should be based on the label approved by the clinical evidence. The research data on lower dosing regimen and longer vaccine interval could be used for the inoculation plan, if need be.”

Korea Disease Control and Prevention Agency (KDCA) plans to review all possibilities, as there is some time left until the vaccine supply arrives and the inoculation starts. The agency official also added, “The detailed would be unveiled later, but the agency is carefully setting up the vaccination plan by referring to experts’ opinions.”