In the face of the Omicron surge, which is likely to take over the festive season, a growing number of countries have resorted to reducing the interval between Covid vaccine boosters from six months to as few as three. This has been done in a bid to ward off a new surge in infections from the Omicron variant.
While data remains limited, half a dozen laboratory studies have shown that an initial course of Covid-19 vaccines typically given in two doses is not enough to halt infection from the Omicron variant, but a booster shot may help.
Many countries, including the United States, earlier this year authorized booster doses at six months after a person completes vaccination.
While many countries like the United States, South Africa, and Germany, have stuck to the six-month booster schedule, South Korea, UK, and Thailand have reduced the interval to three months. France, Singapore, Taiwan, Italy, and Australia have decreased their booster wait time to five months.
These countries are reacting to early evidence suggesting that Omicron is spreading faster than its predecessor, Delta, and is more likely to infect people who were vaccinated or had Covid in the past. Some scientists, however, say that giving boosters too soon could compromise the level of longer-term vaccine protection.
The move to offer the booster shot earlier than the six months initially planned comes amid rising infection numbers and concern over the Omicron coronavirus variant.
The waiting time for Covid-19 vaccine booster shots in Australia has been cut from six months to five in a bid to keep people protected against the newfound virus
South Korea cut the interval for coronavirus booster vaccines for all adults from four to five months to three, officials said on Friday, as it struggles to fight record levels of infections amid concerns over the Omicron variant.
Finland has recommended a three-month booster timeline for at-risk groups, saying it does not believe shortening the time for the general population will slow rising hospitalizations.
Spain and Lithuania are also offering boosters only to people with weak immune systems, the elderly, or vulnerable, while India has not decided on a booster campaign. The World Health Organization, which had told rich countries to prioritize sending first Covid vaccine doses to the developing world, has become more open to boosters in light of rising cases.
More data is needed, but there is a risk that shorter timeframes could compromise the effectiveness of vaccines given in multiple doses, experts said.
“In general for multiple-dose vaccines … the immune system works better if it has time to mature,” said Dr. William Schaffner, infectious disease expert from the Vanderbilt University School of Medicine.
While studies show that boosters temporarily increase antibody levels, scientists say the goal of a vaccine regimen is to elicit not only antibodies but second-line immune system defenses such as T-cells.
“All that is going to be helpful for keeping you out of the hospital,” said Dr. Peter Hotez, a vaccine expert at Baylor College of Medicine.
Multi-dose vaccines prime the immune system, giving it time to marshal those back-up defenses.
Dr. Luciano Borio, a former Food and Drug Administration acting chief scientist, said, “I do worry that we don’t know what impact it may have on the immune system maturation of the doses. Three months seems like a very short interval.”
The United States has no plans to change its current booster timing recommendations, U.S. Centers for Disease Control and Prevention spokesperson Kristen Nordlund said in an email.
“From an immunologic point of view, it does not make sense to shorten the intervals to less than six months,” said a spokesperson for Arkansas’ public health department.
Still, some experts argue that the six-month interval was arbitrary, and data gathered prior to the rise of the Omicron variant in November has shown that immunity, as measured by antibody levels, begins to drop off as early as four months after initial COVID-19 vaccinations.
“Four months is when the waning really started to get substantial,” said Dr. Eric Topol, director of the Scripps Research Translational Institute in La Jolla, California. “Omicron just forces the issue.”
Research from southern Africa and the UK shows that the variant is spreading very quickly, prompting forecasts that it will soon outpace Delta in several countries. Scientists are also trying to determine how severe cases of Omicron are.
(With Inputs from Agencies)