In the United States, vaccinated people are now allowed to visit with other vaccinated people indoors without wearing masks or physical distancing... What do UK experts think about the controversial CDC guidance?

First published in March 2021.

The US Centers for Disease Control and Prevention (CDC) has published the first set of public health recommendations for fully vaccinated people in the United States. The guidance reads that fully vaccinated people can now:

  • Visit with other fully vaccinated people indoors without wearing masks or physical distancing;
  • Visit with unvaccinated people from a single household who are at low risk for severe COVID-19 disease indoors without wearing masks or physical distancing;
  • Refrain from quarantine and testing following a known exposure if asymptomatic.

However, the CDC recommends that fully vaccinated people should continue to:

  • Take precautions in public like wearing a well-fitted mask and physical distancing;
  • Wear masks, practice physical distancing, and adhere to other prevention measures when visiting with unvaccinated people who are at increased risk for severe COVID-19 disease or who have an unvaccinated household member who is at increased risk for severe COVID-19 disease;
  • Wear masks, maintain physical distance, and practice other prevention measures when visiting with unvaccinated people from multiple households;
  • Avoid medium- and large-sized in-person gatherings;
  • Get tested if experiencing COVID-19 symptoms;
  • Follow CDC and health department travel requirements and recommendations.

What the UK experts say.

“The CDC advice will be welcome news to many, and a sign that things are starting to get back to normal. However, it should be pointed out that this new advice is not risk-free. We know that two weeks after two complete doses of the vaccine, people have high levels of protection but they are not completely immune. They will have a lower risk of catching the SARS-CoV-2 infection, they will (almost certainly) have a lower risk of transmitting the virus if they do get infected, and if they are infected they will have a lower risk of severe illness. However, the total risk to the individual is not just about the level of protection they get from vaccination, but also the level of infection in the population – while the level of infection remains high so does the risk.

“Putting numbers to these lower risks is still an ongoing scientific process as we gain more data on the action of the vaccine in real world settings – so it is still too early to quantify the precise risk, but it is clearly not zero.”

“Whether these new guidelines are wise or not depend on a number of factors not least of which is how common the infection is in the community at the time.

It is doubtful that any of the vaccines are highly effective at preventing asymptomatic infection, even though they are high effective at preventing symptomatic illness and especially severe illness. Asymptomatic infected individuals can still pass on the infection, though much less effectively than symptomatic individuals, about 1/3 as likely. In general though the aim in the community is not to prevent every possible transmission but rather to reduce transmission to a point that R becomes less than 1 and case numbers decline, except when particularly vulnerable people are concerned.

“When community transmission is relatively low the new CDC advice is unlikely to pose a significant risk either to the people meeting or to the wider community. Indeed it would not be that different to the rule of 6 that will be allowed in England probably in May, though in England this will be allowed whether or not people have been vaccinated. So to my mind the US guidance has some merit, though I would not argue in favour of changing the UK’s current roadmaps. Indeed if we are able to keep to the timetable contained within the English roadmap we should be allowing general indoor mixing well before the majority of the English population has been immunised with both injections and ahead of the CDC guidance.

“There are a couple of points, however, that concern me:
1. Although mentioned in the text of the guidelines, it should have been made very clear that if anyone has symptoms compatible with COVID, they should still practice self-isolation, get tested and not visit or allow others to visit them whether or not they are vaccinated.
2. The definition of “low risk for severe COVID-19″ where you can visit even if not vaccinated should be a lot clearer than stated in the document. This could be a major source of confusion for many people.

“The big issue however is whether this guidance will remain appropriate if one of the new variants with an escape mutation (a mutation that makes the virus more resistant to prior immunity from either natural infection or immunisation) start to spread rapidly within the US, and there is evidence that at least in some areas this may already be happening.”

A vial of the COVID-19 vaccine. | Flickr/U.S. Secretary of Defense

Easing restriction measures too soon is risky when infection rates are still high and uncertainty remains about the impact of virus variants. The drop in infection rates in the US seen since the start of the year has levelled off over the past week to around 60,000 cases per day with some cities reporting increases. Just over 31 million people have been fully vaccinated in the US. Allowing fully vaccinated people to meet with those who are not vaccinated is asking for trouble – even if the unvaccinated folk are not at high risk of serious disease. It just creates more opportunities for the virus to spread and for people to be generally less vigilant at a time when there are concerns that about the spread of virus variant in New York (B.1.526) that might be more resistant to the current vaccines.”

  • Dr Peter English, Consultant in Communicable Disease Control, Former Editor of Vaccines in Practice Magazine, Immediate past Chair of the BMA Public Health Medicine Committee:

“This guidance comes at a time when increasing numbers of people in the USA have, or soon will have, been fully vaccinated against Covid-19. There will inevitably be demands for information on whether fully vaccinated people can relax their behaviours and whether the restrictions replaced upon them can be reduced.

“The recommendations have to find the right balance between what people will find acceptable, what will allow society to start moving again, and concerns that too much easing of restrictions will allow more widespread transmission of the virus. They have to acknowledge that, while vaccination is good (but not perfect) at protecting the vaccinated person from serious illness, we still do not have enough evidence to be confident of how effective vaccination will be at preventing infection and transmission (although, as the authors acknowledge, evidence is beginning to accumulate to suggest that we can expect some, though not perfect, efficacy in this regard – although many uncertainties, such as the level and duration of such efficacy, remain).

“The recommendations are thus based on the assumptions that fully vaccinated people:

  • are at low risk of serious illness; but
  • could still become infected and infect others, driving transmission rates and causing serious illness in those who are susceptible to it.

“Other considerations appear to include the importance of avoiding spread between households; and that the risk of transmission increases in a non-linear way as the number of people in a gathering increases (double the number of people, and you increase the risk of transmission approximately four-fold).

“The recommendations are pragmatic, based on well-founded (but not fully-proven) judgements about the likely efficacy of vaccines.

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The recommendations accept that some fully vaccinated people will become seriously ill – the efficacy of vaccination against serious illness is very good, but not 100%. They appear to have concluded, however, that the restrictions required to reduce the number of such cases, would be disproportionate; and this seems a reasonable conclusion.

“They are also written with great clarity; and they are clearly labelled as “interim” recommendations, as it is likely that, as our knowledge of vaccine efficacy grows, these recommendations will change.

““Fully vaccinated” is defined so as to that include people who received a single-dose vaccine (such as the Johnson and Johnson/Janssen vaccine) at least two-weeks previously. Given that immunity continues to improve for several weeks, they might have been more cautious, and recommended that people who receive such vaccines should not be considered “fully vaccinated” until, say, at least four weeks after their vaccination date.” 

PMP News reporting

[This piece was first published in PMP Magazine on 9 March 2021. | The author writes in a personal capacity.]

(Cover: Flickr/The White House. - DC Firefighter and EMT Gerald Bunn receives a COVID-19 vaccine from RN Elizabeth Galloway during an event with President Joe Biden, celebrating the 50 millionth COVID-19 vaccination. | 25 February 2021. / Licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.)

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