As families and friends pick up for the holidays and concern for a winter surge grows, it’s no coincidence that public health officials and federal and local leaders have made the big push last week to expand COVID-19 vaccination boosters for all adults
But as more people get additional shots, a big question lurks in the background: how long will the boosters last?
Anthony Fauci, the country’s top expert in infectious disease, said Sunday on ABC that the hope is that boosters will offer long-lasting protection so additional doses are not needed.
“We hope, and this is something we look at very carefully, that the third shot with the MRNA not only boosts her way up, but increases the arms so that you will not necessarily need it every six months or a year” he said , Referring to the Pfizer and Moderna vaccines, which use the same messenger RNA platform. “We hope it pushes it more.”
But right now, the longevity of booster doses is unknown, and the finding it will take some time.
“We know very little about how long boosters last,” Julie Parsonnet, a Stanford expert in epidemiology and population health, told the Chronicle in an e-mail. “The hope is that further vaccinations will be unnecessary, but we do not have any evidence yet to support that hope.”
Is still early in his boost campaign, “so we need time to be able to say how long-lived immunity will be after the third dose,” said Nadia Roan, an investigator at the Gladstone Institutions in San Francisco, who is studying vaccination. Induced immunology, in an e-mail.
In mid-August, the FDA granted emergency use clearance for a third vaccine dose for immunocompromised people, and in late September, the same for older people and others at high risk for severe infection.
Roan said there is a chance that all we need is three doses, but “it is also possible that repeated cowid vaccine boosting may become a regular thing,” like the annual flu vaccine.
Parsonnet said another concern is whether coronavirus variants arise that escape vaccination immunity.
“With this we know more generally about coronaviruses, I suspect that we may need occasional revaccination,” she said.
What we do know is that boosted people are “more protected from overall breakthrough infection than non-boosted vaccinated people,” Roan said.
“Now we know that vaccination in six months is safe and effective,” she said. “We also know that the vaccines disappear a bit over this time. This is the reason why the time was chosen.”
According to Parsonnet, Israel’s booster rollout offers lessons that show that third shots are effective early on. The country, which uses the Pfizer vaccination, approved boosters for older people in late July, and began offering them to everyone 16 and older at the end of August.
“Given the day of start of third dosing, we will see six-month efficacy rates sometime in the late winter,” she said, adding that information about wanting antibody levels may come sooner. “The efficacy rates will begin to indicate whether further shots will be needed.”
She said she does not expect any useful information about Moderna and Johnson & Johnson boosters, which will roll out later, until next summer. But if the data look promising, researchers will examine numbers at the nine-month and one-year marks.
Another big issue is the dosing intervals, which Parsonnet said is an even tougher challenge.
“In the past, there was no rush to vaccinate everyone, so we have the luxury to try multiple strategies,” she said. “But with COVID, we have needed fast forward. It can take years to know what the optimal dosing intervals are.
She said that we will first find the right dosage of the third shot, because people will get the shot at different intervals: some may get them right six months after their second dose, and others will wait longer.
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Roan said she did not think waiting six months or eight months would make a significant difference because the memory cells (called B and T cells) were already formed.
“What the third dose will do is to awaken the memory cells, and get them to expand in numbers, and in the case of B cells, start producing antibodies again,” she explains. “The elevation in antibody levels after boosting provides a strong first line of defense against breakthrough infection.”
The antibodies will not last forever at high levels, but the immune cells’ memory will be more long-lasting, which is “important in providing protection against severe COVID-19,” she said. This is why despite wandering immunity after the second vaccine dose, the vaccine continues to provide strong protection against hospitalizations and death.
Roan said boosters are probably most beneficial for immunocompromised people who have not had an antibody response to the first two doses of MRNA vaccines and are able to release some antibodies after a third dose.
However, Parsonnet said, some immunocompromised people may never respond to vaccines, no matter how many doses they receive, with quote reports that have shown only half of immunocompromised people have responded to third doses. So it’s important that all adults receive an additional vaccine dose to protect everyone, Parsonnet said.
We see enough breakthrough infections – a small proportion of which are serious – in the general population that boost everyone will prevent serious illness in the vaccinated and, perhaps even more importantly, limit the transmission to those who do not respond effectively to vaccines . “
Kellie Hwang is a San Francisco Chronicle staff writer. Email: kellie.hwang@sfchronicle.com Twitter: @KellieHwang
