How protective is one dose of the covid vaccine?

January 15, 2022 6:35 PM

My five-year-old got his first dose over the Christmas break and is not yet eligible for his second dose. School re-opens on Monday and I am terrified. In this 'pandemic of the unvaccinated' how protected will he be as a half-vaccinated person?

Alas, it is not an option to keep him home. He is generally in good health but was diagnosed with asthma recently. I've read every article I can find and they all just repeat that vaccination is important and we should totally do it. They don't address the grey area of one dose given but not yet two...

posted by ficbot to Health & Fitness (6 answers total)

I don't know where you are, but right now even with fully unvaccinated people under the age of 5, the hospitalization rate across the entire US for those 0 - 4 is only 5 per 100,000 people per week. Right now, in my area, the hospitalization rate for those who are older and fully vaccinated varies from 1.9 per 100,000 people per week (12-34) to 4.8 per 100,000 people per week (35-64) to 13.4 per 100,000 people per week (65+).

Even if you assume the first dose for your five year old is completely useless, your child is at most at a similar COVID risk as you - and probably even lower risk.

Note these numbers are across the broad US population, which include those with asthma.
posted by saeculorum at 6:52 PM on January 15, 2022 [5 favorites]

Possible useful search term is "waning immunity" - but I think this is still after two doses.
posted by freethefeet at 7:00 PM on January 15, 2022

I follow Emily Oster on Twitter who writes a lot about young children and Covid. There’s a lot you can find if you scroll through her Twitter of substack newsletter. She’s one of the founders of Covid Explained and has been writing about the data data coming out about children and Covid since the start of this whole thing. It sounds like the first vaccination is quite protective against getting seriously I’ll or hospitalization. Also sounds like asthma has not been a factor as well. That said, I don’t blame you for feeling worried. Do you have access to some good kid sized KN95s?
posted by biscuits at 7:02 PM on January 15, 2022 [1 favorite]

Here's a 2021 study that focuses on the effectiveness of single dose mRNA vaccination.

It includes detailed statistics on how much protection a single does conferred to health care workers, and is probably the best serious analysis of single-dose effectiveness in a two-shot regimen, even though it is obviously not the same age group.

It makes the Conclusion: One mRNA vaccine dose provided substantial and sustained protection to HCWs extending at least four months post-vaccination. In circumstances of vaccine shortage, delaying the second dose may be a pertinent public health strategy to consider.

Please don't use general population figures to answer your question, they have almost nothing to do with the issue of single-dose mRNA vaccine effectiveness at preventing disease, hospitalization, or death.
posted by SaltySalticid at 7:27 PM on January 15, 2022 [1 favorite]

Here's a 2021 study that focuses on the effectiveness of single dose mRNA vaccination.

The study period for that one predated omicron, fwiw.

I follow Emily Oster on Twitter who writes a lot about young children and Covid.

She's an economist who decided in May 2020 that there was enough evidence to say that "in practice it seems that infection among kids is simply very unlikely." This turned out to be very wrong, so I am a bit skeptical of her.

Without regards to age, the NHS reports that "When combined with vaccine effectiveness against symptomatic disease this was equivalent to vaccine effectiveness against hospitalisation [by Omicron] of 58% after one dose." (page 24) So, people with one dose 58% less likely to be hospitalized than people with no dose (this is how "vaccine effectiveness" is defined). 5 year olds are mostly not getting vaccinated in the UK, so it's not directly on point, but it is evidence that a single dose does generally still protect against hospitalization with omicron, at least in older people. I don't think it's valid to generalize the specific number to children, but at least it's something.
posted by BungaDunga at 11:59 AM on January 16, 2022

Look at tables 10 and 11 here. It does seem that in New York State at least, for 5-11 year olds the week of December 20-26, 5% of new covid cases are fully vaccinated, 13% are partially vaccinated, and 83% are unvaccinated. Similarly, among that age group for that same week, for new COVID-19 hospital admissions, the percentages are 4%, 6%, 91%, respectively. The note does point out that in previous weeks <1% of this age group was fully vaccinated (and it's worth considering the fact that vaccinated and unvaccinated youth may be fundamentally different at the population level), so perhaps it's worth comparing the relative values for the 12-17 year age group as well.
posted by oceano at 4:31 AM on January 17, 2022