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 They 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.
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.
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.
Many countries, including the United States, earlier this year
authorized booster doses at six months after a person completes
vaccination. This month, South Korea, the United Kingdom and
Thailand cut that interval to three months. Belgium has lowered it
to four months.
France, Singapore, Taiwan, Italy and Australia have decreased their
booster wait time to five months.
Some countries, including the United States, South Africa and
Germany, have stuck to the six-month booster schedule.
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 so far 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.
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IMMUNE SYSTEM DEFENSES
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."
(Additional reporting by Carl O'Donnel and
Michael Erman in New York; Olivia Kumwenda in
Johannesburg; Aradhana Aravindan in Singapore;
Rocky Swift in Tokyo; Ben Blanchard in Taipei;
Krishna Das in New Delhi; Ari Rabinovitch in
Israel; Francesco Guarascio in Brussels; Clara-Laeila
Laudette in Madrid; Essi Lehto in Helsinki;
Josephine Mason in London; editing by Caroline
Humer, Michele Gershberg and Cynthia Osterman)
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