Covid Spread Similar Regardless of Vax Status

November 1, 2021


The only consensus on vaccines is that there is no consensus on vaccines. So why mandate them?


A blow to mandates: Study shows the vaccinated transmit the virus at home almost as much as the unvaccinated do

There are two arguments for employer vaccine mandates. One focuses on the fact that COVID is, after all, a highly contagious disease and the unvaccinated are more infectious than the vaccinated are. To reduce transmission in the workplace, everyone needs to do their part by getting the shots. It’s not just your health you’re playing with by refusing to get immunized, it’s your colleagues’. Your right to throw a punch ends at my nose.

The other argument is that it’s for your own good. Plenty of data shows that vaccination significantly reduces your odds of developing a severe case of the disease. Ask an ICU doctor about his patients with COVID and he or she will tell you that the great majority are unvaccinated, especially the ones who are younger and/or have no other underlying health problems. If you’re too pigheaded to protect yourself by getting the shot voluntarily, your boss will try to protect you by threatening your job if you don’t comply.

Americans don’t like “for your own good” arguments. That slope is slippery, after all. If your company can tell you to get the jab because it needs you healthy and on the job, presumably it can tell you to quit smoking or eat healthy or lose weight or drive more slowly or do a hundred other things that will extend your lifespan. If we want to avoid going down that path, we need to stick to the first rationale. Vaccine mandates are a special case because they involve a situation in which one person’s health depends on another’s.

But what if, in the age of Delta, vaccination doesn’t dramatically reduce transmission? That would weaken the first argument in favor of mandates since it would mean that you getting the shots doesn’t do much to protect my health. *My* getting the shots does a lot to protect my health. So why should you have to be immunized if you don’t want to be?

new (and small) study from the UK tracked people and their household contacts for a year to see if vaccination reduced transmission within households. Answer: It did, and it also reduced the severity of disease in people who were vaccinated. But the effect on transmission wasn’t night-and-day. Which raises the question: Are employer vaccine mandates more trouble than they’re worth?

The SAR [secondary attack rate] in household contacts exposed to the delta variant was 25% (95% CI 18–33) for fully vaccinated individuals compared with 38% (24–53) in unvaccinated individuals. The median time between second vaccine dose and study recruitment in fully vaccinated contacts was longer for infected individuals (median 101 days [IQR 74–120]) than for uninfected individuals (64 days [32–97], p=0·001). SAR among household contacts exposed to fully vaccinated index cases was similar to household contacts exposed to unvaccinated index cases (25% [95% CI 15–35] for vaccinated vs 23% [15–31] for unvaccinated). 12 (39%) of 31 infections in fully vaccinated household contacts arose from fully vaccinated epidemiologically linked index cases, further confirmed by genomic and virological analysis in three index case–contact pairs. Although peak viral load did not differ by vaccination status or variant type, it increased modestly with age (difference of 0·39 [95% credible interval –0·03 to 0·79] in peak log10 viral load per mL between those aged 10 years and 50 years). Fully vaccinated individuals with delta variant infection had a faster (posterior probability >0·84) mean rate of viral load decline (0·95 log10 copies per mL per day) than did unvaccinated individuals with pre-alpha (0·69), alpha (0·82), or delta (0·79) variant infections. Within individuals, faster viral load growth was correlated with higher peak viral load (correlation 0·42 [95% credible interval 0·13 to 0·65]) and slower decline (–0·44 [–0·67 to –0·18]).

If I’m reading that correctly, vaccinated people spread the virus to household contacts as much as unvaccinated people did. Among those household contacts, the vaccinated were somewhat less likely to get infected than the unvaccinated were. Across both groups, the vaccinated cleared the virus more quickly than the unvaccinated, which presumably made them contagious for shorter periods.

Assuming all of that is true, the case for mandates is weakened. Vaccinated workers will still infect co-workers, possibly as much as unvaccinated workers will. On the other hand, a company that’s worried about ending up short-staffed due to a workplace outbreak of COVID has some incentive to mandate the vaccine anyway. It’s not true, after all, that COVID is exactly equivalent to smoking or unhealthy eating even if the vaccines don’t reduce transmission, as I implied up above. Health problems related to weight or smoking don’t crop up simultaneously in many employees and force them to take sick leave at the same time, potentially bringing a business to its knees.

There’s also the problem (which has become familiar during the pandemic) of different studies saying different things. Another study from the UK that examined 150,000 records compiled by contact-tracers found that vaccination did matter a lot to transmission: “When infected with the delta variant, a given contact was 65 percent less likely to test positive if the person from whom the exposure occurred was fully vaccinated with two doses of the Pfizer vaccine.” Maybe the distinction between the two studies has to do with length of exposure. Household contacts are around an infected person for many hours but casual contacts aren’t. It may be that vaccination significantly reduces transmission during limited exposure but not so much during prolonged exposure — which, again, would undercut the argument for workplace mandates.

Exit question: How do boosters fit into all of this? Same minimal effect on transmission or does a third dose meaningfully reduce infection? We’ll need more studies to know. I’m not looking forward to the mandate debate if it turns out that only by getting a third dose can employees truly make their workplace safe.