Omicron expansion leads some countries to reduce deadlines for COVID-19 booster vaccines

A growing number of countries are reducing the wait time for COVID-19 vaccine efforts from six to three months in an attempt to prevent a further increase in omicron infections.

The reaction comes from preliminary 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.

However, some scientists say that giving boosters too early could compromise the level of protection of the vaccine in the longer term.

While data remains limited, half a dozen laboratory studies have shown that an initial cycle of COVID-19 vaccines, usually given in two doses, is not enough to stop omicron infection, but a booster injection can help.

Research in southern Africa and the UK shows that the variant is spreading very rapidly, leading to forecasts that it will soon overtake Delta in several countries. Scientists are also trying to determine how serious omicron cases are.

Many countries, including the United States, authorized booster doses earlier this year six months after a person completes vaccination. South Korea, the United Kingdom and Thailand cut that interval to three months in December. Belgium has lowered it to four months.

Meanwhile, France, Singapore, Taiwan, Italy and Australia have reduced their waiting time for reinforcement to five months.

Some countries, including the United States, South Africa, and Germany, have stuck to the six-month booster program.

Finland, meanwhile, recommended a three-month booster schedule for at-risk groups, saying it does not believe that shortening the time for the general population will slow the rise in hospitalizations.

Spain and Lithuania are also so far offering boosters only to people with weak, elderly or vulnerable immune systems, while India has not settled on a booster campaign.

More data is needed, but there is a risk that shorter time frames will compromise the efficacy of vaccines given in multiple doses, experts said.

“In general, for multi-dose vaccines the immune system works better if it has time to mature“, He said Dr. William Schaffner, an infectious disease expert at 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 also second-line immune system defenses, such as T cells.