A fourth COVID-19 vaccine has been licensed for people over 50 as well as immunocompromised under 50s. The clearance comes as BA.2, a sub-variant of omicron, is spreading across the world and intensifying in parts of the United Statesraising concerns about the duration of immunity after a booster.
The latest evidence suggests that levels of antibodies, which protect us against infection, decline around four months after a booster shot. T cells, the part of our immune system that protects us against serious illness, show a slight decline after four months but remain robust. This decline does not mean that we are no longer protected; real-world data shows that the vast majority of people who have received three doses are incredibly well protected from hospitalization (a 90% risk reduction) several months after their last dose.
“In three to four months it will start to go down, but you’ll still be in pretty good shape,” said Otto Yang, a professor of infectious disease medicine at UCLA’s David Geffen School of Medicine.
Here’s how quickly antibody levels drop and what that means for your next booster:
How long do antibodies last?
Data on antibody levels are limited and not well understood, but it appears that antibody levels decline, on average, about four to six months after a booster shot.
A recent Centers for Disease Control and Prevention study suggests that vaccine effectiveness begins to decline about four months after a booster dose (which is likely due to falling antibody levels). Among people who received three doses during the delta wave, vaccine effectiveness against urgent care and emergency room visits was 97% within two months of vaccination; which fell to 89% after four months.
During the omicron wave, vaccine effectiveness against hospitalization in people who received three doses was 91% within two months of their last dose and 78% after four months. A paper from the UK published in The Lancet Last July, antibody levels after two doses were found to decline after two to three months, although antibody levels were still quite high at that time with the Pfizer vaccine (higher than with AstraZeneca injections). A report published in the New England Journal of Medicine in January 2022 found that although antibody levels declined six months after a Moderna booster, the remaining antibodies were still able to successfully fend off the omicron.
At this stage, scientists are unclear whether there is a specific antibody level that would indicate a person is well protected against infection – although it is clear that higher antibody levels generally equate greater protection against infection. What we do know is that even in the face of decline, most people who received booster shots continue to be safe from serious illness, hospitalization and death.
Research shows that the rate at which antibody levels decline is somewhat influenced by age, gender (antibodies decline faster in men), and immunosuppressive health conditions. But Yang, who studies our immune response to COVID-19, said he’s seen 100-year-olds with long-lasting antibody levels — so it’s not always so black and white.
Our T cell response is long lasting and longer lasting
Protection against COVID-19 does not depend solely on antibodies. Where antibodies protect us from infection, T cell response protects us from serious illness and death. And according to Monica Gandhiinfectious disease specialist at the University of California, San Francisco, it seems that T cell immunity will last a long time, even against variants. Several studies have found that T cell responses remained almost as effective against omicronsix months after vaccination, as they were against earlier variantssaid Gandhi.
Yang, who studies T-cell responses, noted that T-cells may start to decline after a few months, but that doesn’t mean they’re gone. “About three to four months after the third vaccine, after the first booster, the benefit of the vaccine preventing serious diseases begins to decline, but does not drop precipitously,” Yang said.
If an antibody test has shown that a person has no detectable antibodies, that means there are no antibodies circulating in their blood. It’s a bit more complicated when it comes to testing T cells. T cells have excellent memory, so even if a generally healthy person has weak or undetectable T cells, they can reappear, multiply very quickly and take action. That’s probably why real-world data shows the vaccine still protects most people. serious illness and death.
Should you time your next booster for future waves?
It is at the time of the recall that it becomes delicate, because the doctors have different grips.
Yang recommended getting the second booster, meaning a fourth dose, as soon as you are eligible. Although we’re in a lull, COVID-19 is still circulating and you don’t want to have weak immunity when exposed, especially if you’re at risk, he said. It could also help prevent future waves.
“If you have already tolerated three doses of the vaccine without any serious problems, you will almost certainly tolerate the fourth dose – there are so few downsides, it is worth getting it,” Yang said.
Something else to consider, according to Yang: We even need higher levels of antibodies to combat these new variants, as they are structurally different from the original strain targeted by the vaccines. “That’s probably one of the reasons the boosters were recommended so quickly,” he said.
Gandhi, on the other hand, recommends scheduling your boosters for future waves (which she personally advises her parents, who are older and at risk, to do). “You want your antibodies to be plump and high, especially if you’re vulnerable, at the time of typical flare-ups,” Gandhi said.
Officials believe COVID-19 could become a seasonal disease. However, seasonality varies from region to region – while the Northeast typically experiences surges in early fall and winter, southern regions like Florida tend to experience summer surges when the air hot, sticky and humid sends people inside.
If in doubt, talk to your doctor. Most people who have had three injections will still be well protected against serious consequences such as hospitalization and death. But for the elderly, immunocompromised, and people with health conditions that put them at higher risk, it’s worth hearing your doctor’s perspective on how the benefits of getting a fourth dose now combine with the risks of postponing it a little longer.