New Data Suggest Covid Booster Shots Significantly Increase Protection

The two-dose regimen was an estimate of what might be optimal given the impact of the virus, the number of people who needed to be vaccinated and the amounts of vaccine initially available.

The most recent analyses suggest that a third shot, rather than a mere top-off, could be crucial to long term protection from Covid. JL

Josh Marshall reports in Talking Points Memo:

It’s possible that a booster isn’t just a top off that gets you back to the peak immunity you had a couple weeks after your second shot, only to see it fade. It’s possible  that third shot gives you more durable immunity than the initial two. If two doses was pretty good, that was a big mark in its favor since you can’t get people pretty good protection quickly, rather than waiting a few months. Existing science didn’t clearly dictate a particular time interval. Given that uncertainty, speed would save lives. Data from Israel shows more abundant and more long-lasting antibodies after a booster shot. The boosters last 9 to 10 months, as opposed to the quicker drop off with the two dose regimen.

There’s little question that a COVID booster shot increases your immunity to COVID infection. Data out of Israel from the late summer and early fall leaves little question about that. The public debate – setting aside questions of global vaccine equity – has been about how long that increased protection lasts and whether it matters. Let’s take the second part first. The most important protection you get from COVID vaccination is protection against severe illness and death. A year’s worth of data shows that protection against bad outcomes remains robust even though protection against infection declines substantially after about 6 months. For healthy people under 65 is it worth another round of vaccination, especially if that top off of increased protection only lasts a few months?

That’s the skeptics’ argument. But in the background to the booster debate is a another question that doesn’t get as much attention. The standard regimen of two shots three or four weeks apart wasn’t set in stone or a certain choice driven by the existing science on mRNA vaccines. Specialists I’ve spoken to refer to it more as an educated best guess. Critically, optimal dosing wasn’t the only consideration that went into the two dose regimen we’re familiar with. The choice was also driven by the evolving COVID crisis and the priority to get clinical trials done as quickly as possible. If the clinical trials over the course of 2020 had waited three months between injections that just adds another two or three months before life-saving vaccines could be approved for public use. A comparable logic applied for the roll out itself. If two doses was pretty good, that was a big mark in its favor since you can’t get people pretty good protection quickly, rather than waiting a few months. I don’t mean to suggest the specialists choosing the dosing chose a suboptimal plan. It’s simply that existing science didn’t clearly dictate a particular time interval. Given that uncertainty, speed would save lives.

The point is we don’t know that the two shots a few weeks apart is the optimal dosing regimen. It’s possible that a third dose a few months after initial vaccination (or perhaps two doses over a longer period) was always the optimal regimen. This wouldn’t be a great surprise. Many other vaccines include a booster a significant length of time after the initial dose. Indeed, there’s some limited evidence from countries that spaced out their initial two shots (because of vaccine scarcity) that a longer interval does provide heightened immunity.

What this all means is that it’s possible that a booster isn’t just a top off that gets you back to the peak immunity you had a couple weeks after your second shot, only to see it fade over 5 or 6 months. It’s possible that that third shot gives you more durable immunity than the initial two.

Needless to say, short term top off versus durable increase in immunity is a pretty big deal. Israel is now about four months out from the beginning of its booster program. So I’ve been watching to see if and when this data emerges. To the best of my knowledge there are currently no robust studies published which shed light on this critical question. (If you’re aware of such a study please let me know.) With Israel beginning it’s booster program in July the end of the calendar year should produce the first solid data on this question.

What I did just see however is a study out of the United Kingdom which looks at a distinct but related question. This study showed that immunity after a Pfizer booster was significantly higher than the immunity conferred after two shots. Two weeks after a second Pfizer shot, protection against symptomatic infection was 82%. That fell to 63% after 5 months. But two weeks after a booster (i.e., a third) shot, the protection rose to 93-94%. In other words, protection after a third shot was substantially higher than after two shots even at its peak.

Then just this morning a news report out of Israel says that data from a soon-to-be-released study also shows more abundant and more long-lasting antibodies after a booster shot. Preliminary data also suggests the boosters likely last 9 to 10 months or longer, as opposed to the quicker drop off with the two dose regimen. This is all preliminary data. Indeed, it’s pre-preliminary inasmuch as it’s a report leaked in advance of publication. We don’t know the details of the Israeli study. But it does seem to show something similar to the findings out of the United Kingdom and is the first sign that protection from a booster is more durable than that from the two dose regimen.

Have you gotten a booster yet? It’s probably time.