BY OSAMU TSUKIMORI, STAFF WRITER
Japan began implementing a mix-and-match COVID-19 vaccine strategy last month, with some health care workers who received the Pfizer-BioNTech jab for their first two shots getting Moderna Inc.’s shot as a booster, as the government aims to accelerate the rollout of third shots amid heightened concerns over the omicron variant.
Like the European Union, the Japanese government is recommending people receive a different jab for their third doses to the one they received in the initial rollout, but what’s the rationale behind that strategy? Here are some answers to address the most common questions about booster shots:
What do boosters offer in the way of added protection?
Studies have shown the vaccines’ efficacy against infection starts to wane significantly after as little as three months — especially among people age 65 and older — and the U.S. Centers for Disease Control and Prevention says the alarming spread of the omicron variant further emphasizes the importance of boosters, although two doses remains effective when it comes to preventing severe disease and death.
Unlike Pfizer’s vaccine, a Moderna booster is only a half dose of the vaccine used for initial shots, as the lower dosage is enough to sufficiently boost people’s immune systems.
Experts say vaccines remain critical to reducing severe disease and death, urging eligible residents to get third doses as soon as possible amid mounting evidence of their importance.
A study in Israel — the first country to roll out booster doses — showed that the rate of COVID-19 infections among people age 60 and older who received Pfizer’s booster shot at least five months after their second doses of the firm’s vaccine was lower by a factor of 11.3. Additionally, the rate of severe illness was lower by a factor of 19.5.
People who received a Pfizer-made booster after their two initial vaccine shots from a different drugmaker were shown to have stronger immune response capability. Pfizer has also said its initial laboratory study demonstrated that antibodies generated by a booster shot neutralize the omicron variant.
Similarly, people who received the Moderna booster after getting two Pfizer shots also saw their neutralizing antibodies increase by 31.7 times, compared with a twentyfold increase for those who stuck with the Pfizer shot as their third dose, according to a U.S. study published on the medRxiv preprint server for health sciences. It’s important to note, however, that the study used the full Moderna dose as a booster, unlike the half dose used in actual practice.
The Australian Technical Advisory Group on Immunisation says there are no published studies that directly compare the protection offered by Moderna’s half dose with other vaccines used as a booster.
Which vaccines are available for booster shots and who is eligible?
First and second doses of the Pfizer and Moderna vaccines have been authorized for use in Japan for people age 12 and older, while AstraZeneca’s jab has been approved for people age 40 and over, in principle. But for booster shots, only Pfizer and Moderna’s messenger RNA vaccines have been authorized and only for people age 18 and over who are at least six months removed from their initial doses.
People who have received two doses of vaccines made by Pfizer or AstraZeneca PLC can get Moderna’s booster through workplace vaccinations and other local mass vaccination sites or via their local health care providers. Those who received their first and second shots overseas can also get Moderna’s booster in Japan, the health ministry says, as long as their first two shots were with the jabs by Pfizer, Moderna or AstraZeneca.
The government and doctors recommend that all eligible residents get the vaccine. The health ministry highly recommends a booster for elderly people and those with medical conditions who are at a higher risk of developing serious COVID-19 symptoms. Nursing care and medical workers who are at a higher risk of exposure to the virus are also strongly advised to get the booster shot.
“There’s evidence supporting the efficacy of a booster shot whether it be Moderna or Pfizer’s, especially for people with existing medical conditions or the elderly,” said Dr. Tetsuo Nakayama, a project professor at Kitasato Institute for Life Sciences and director of the Japanese Society of Clinical Virology.
The health ministry recommends pregnant or breastfeeding women get the shot as there have been no reports that the COVID-19 vaccines approved in Japan have had an adverse impact on pregnancy, the fetus or breast milk.
The Japan Association of Obstetricians and Gynecologists recommends pregnant women get their initial two doses if they haven’t done so already, adding that they can get booster shots in the same manner as the rest of the population.
What’s the schedule for the rollout of booster shots?
The rollout of booster shots began on Dec. 1, starting with health care workers. Some local governments on Dec. 17 started approving Moderna booster shots for health care workers. During the initial vaccine rollout last year, many hospitals and vaccination sites set up by local governments mostly administered the Pfizer jab, but they will be allocated both Pfizer and Moderna’s vaccines for booster shots as the government increases its reliance on the latter.
For the first two jabs, the number of Pfizer shots outnumbered Moderna’s by a ratio of around 5 to 1, according to calculations based on Cabinet Secretariat data. But that ratio is set to be around 3 to 2 for booster shots, according to Noriko Horiuchi, the minister in charge of vaccines.
Amid consensus in the medical industry that the ideal timeline for a booster is six months or even earlier than that after the initial doses, Prime Minister Fumio Kishida has aimed to shorten the interval to six or seven months for 31 million people on the country’s priority list, including health care workers and the elderly, from the initial plan of eight months.
Residents who have received their initial shots will receive booster vaccination tickets from their local government and some may be able to decide which vaccine they want to receive and where. Workplace vaccination sites are also set to be launched as early as February and will inoculate workers with Moderna’s vaccine.
What are the most common side effects?
Studies have shown that booster shots are safe, with most side effects being the same as those experienced by recipients of initial doses, including temporary fever, headache or pain at the spot where the jab was given.
Some studies have raised concerns about myocarditis and pericarditis — inflammation of the heart muscle and the tissue surrounding the heart, respectively — especially among young people given the shot. Such incidents have been slightly more common with the Moderna jab, but the half dose of Moderna is expected to lower the risk of these very rare heart issues, according to the U.K. Health Security Agency.
“Data suggests adverse reactions following a booster dose should be a little milder than or around the same as those of the second dose,” Nakayama said. “So if you’re concerned (about adverse reactions), then you could try to get a Pfizer jab. Whichever you choose, I would recommend that you do not miss a chance to get vaccinated, especially if you are elderly.”